Q stringlengths 18 13.7k | A stringlengths 1 16.1k | meta dict |
|---|---|---|
Why does the sound pitch increase on every consecutive tick at the bottom of a filled cup of coffee? Since I don't know the proper physical terms for this, I describe it in everyday English. The following has kept me wondering for quite some time and so far I haven't found a reasonable explanation.
When you fill a cera... | I first noticed this in a hot cup of Horlicks, made with milk. I would stir in the powder vigorously, then tap the bottom of the cup with the spoon to check that all the powder had dissolved. Even two taps, one second apart is enough to detect the rising pitch. It continues rising and rising over the course of, perhaps... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23038",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "32",
"answer_count": 4,
"answer_id": 0
} |
Are we inside a black hole? I was surprised to only recently notice that
An object of any density can be large enough to fall within its own
Schwarzschild radius.
Of course! It turns out that supermassive black holes at galactic centers can have an average density of less than water's. Somehow I always operated u... | The entropy of a black hole is maximized. This is not the case for the matter that makes up the Earth; the entropy is not zero, but it's not maximized either. Thus, we do not live in a black hole.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23118",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "62",
"answer_count": 12,
"answer_id": 10
} |
Is chaos theory essential in practical applications yet? Do you know cases where chaos theory is actually applied to successfully predict essential results? Maybe some live identification of chaotic regimes, which causes new treatment of situations.
I'd like to consider this from the engineers point of view. By this I ... | I think it depends on the meaning of "application". In the wikipedia entry there are a lot of applications of chaos theory listed:
Chaos theory is applied in many scientific disciplines, including: geology, mathematics, microbiology, biology, computer science, economics, engineering, finance, meteorology, philosophy, ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23160",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
What are some ways that humans could have influence over what sequence a star was in? How would a society go about either preventing our sun in its primary sequence from going into a Red Giant a billion years from now? Or perhaps, accelerating the process of going from main sequence of our start to a red giant premat... | Sci-fi method: It might still be a competitive in terms of energy expenses options to put all the people into a spacecraft, attain ultrarelativistic velocities, wait a second (or some other necessary time), and then come back to what is left from the Earth. Due to special relativistic time dilation effects during the f... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23484",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
Why does a glass rod when rubbed with silk cloth aquire positive charge and not negative charge? I have read many times in the topic of induction that a glass rod when rubbed against a silk cloth acquires a positive charge. Why does it acquire positive charge only, and not negative charge?
It is also said that glass ... | This is because glass is above silk in the triboelectric series (attracts electrons less than silk) and when rubbed, silk 'takes' its electrons.
And yes, if you had a silk rod it would also attract neutral paper, because paper pieces are turned into dipoles, as you explained.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23515",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "26",
"answer_count": 5,
"answer_id": 0
} |
How does an object regain its neutrality after being charged by rubbing? Objects (like combs) can be charged by rubbing as charged particles, particularly electrons, are transferred from one object to other. This can be seen as the object (comb) attracts small bits of paper. After some time, the charge on the body seem... | Static Electricity
Static electricity is the opening of the fabric of space, or of very tiny black holes in the fabric of space time.
The attractiveness of matter or objects are being pulled into these little opening of fabric of space until the holes close as the fabric of space regain it's ground or natural state.
Ra... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23572",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 4,
"answer_id": 3
} |
How to derive addition of velocities without the Lorentz transformation? Lorentz contraction and time dilatation can be deduced without Lorentz transformation. Can you deduce also the theorem of addition of velocities
$$w~=~\dfrac{u+v}{1+uv/c^2}$$
without Lorentz transformation? Using just the constancy of light spee... | I endorse Ron's answer – it's the systematic way to proceed. The velocity $v/c$ may be written as $\tanh \eta$ where $\eta$, the rapidity or whatever, is the hyperbolic (Minkowski) counterpart of the (Euclidean) angle. The addition of velocities then boils down to an addition formula for $\tanh(\eta_1+\eta_2)$ because ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23625",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "16",
"answer_count": 3,
"answer_id": 2
} |
Can relativistic kinetic energy be derived from Newtonian kinetic energy? Relativistic kinetic energy is usually derived by assuming a scalar quantity is conserved in an elastic collision thought experiment, and deriving the expression for this quantity. To me, it looks bodged because it assumes this conserved quantiti... | Assuming energy conservation isn't "bodged" because at the most fundamental level, energy is defined as the quantity that is conserved as the result of the time-translational symmetry. All specific formulae for energy, such as $mv^2/2$ in nonrelativistic mechanics, are just solutions to the problem "find a conserved qu... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23720",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
What's wrong with this equation for harmonic oscillation? The question:
A particle moving along the x axis in simple harmonic motion starts
from its equilibrium position, the origin, at t = 0 and moves to the
right. The amplitude of its motion is 1.70 cm, and the frequency is
1.10 Hz. Find an expression for the... | The cosine has more than one zero. And the text specifies that the particle goes to the right (I assume that the x axis also goes to the right). Now in which direction does the cosine go at $\pi/2$? And where's another zero?
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23811",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Why there is a $180^{\circ}$ phase shift for a transverse wave and no phase shift for a longitudinal waves upon reflection from a rigid wall? Why is it that when a transverse wave is reflected from a 'rigid' surface, it undergoes a phase change of $\pi$ radians, whereas when a longitudinal wave is reflected from a rigi... | Here is another possible way of explanation:
Reflection of the wave is similar process as crushing two waves, one from the left and one from the right, which meet exactly at the surface. Now, if you wish that particle at the surface has zero displacement, then the wave on the right must be point-symmetrical through th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23847",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "14",
"answer_count": 3,
"answer_id": 1
} |
Equations instead of psychrometric charts I want to create a program that will accurately simulate a condensor. I want to use the data in psychrometric charts. But I cannot and hence want to use equations that show similar data. Any idea where to start?
| There are existing software libraries of psychrometric functions available. These could be suitable for use directly, or at least as points of reference if for some reason you need to create your own. i.e., you can inspect the formulae, coefficient values, etc.
One set of psych equations is the PsychroLib project:
htt... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23917",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Why is glass a good conductor of heat? AFAIK Glass is insulator, it doesn't have free electron. It's said metal is a good conductor of heat because it has free electron, glass doesn't have free electron, why it is a good conductor of heat?
| There are at least two mechanism of thermal conductivity - free electrons and thermal phonons. The first mechanism can be prevalent in metals, the second one is important in dielectrics. I did not look up thermal conductivity of glass, but such excellent dielectric as diamond has higher thermal conductivity than any me... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/23946",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 2,
"answer_id": 1
} |
Is the Avogadro's constant equal to one? Question: Is the Avogadro's constant equal to one?
I was tasked with creating a presentation on Avogadro's work, and this is the first time I actually got introduced to the mole and to Avogadro's constant. And, to be honest, it doesn't make any mathematical sense to me.
1 mole =... | Yes it's a little odd to have a unit of 'amount'. At least in English, it might make more sense in other languages
The second line is really "Avogadro's constant = 6.022 * 10^23 * items/mole"
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/24034",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "17",
"answer_count": 4,
"answer_id": 2
} |
Operators Uncertainty $\hat A$ is an operator.
The uncertainty on $\hat{A}$, $\Delta A$ is defined by:
$$\Delta A=\sqrt{\langle\hat A^2\rangle - \langle\hat A\rangle^2}$$
what is difference between
$\langle\hat A^2\rangle$ and $\langle\hat A\rangle^2$
that leads to Uncertainty Relation between two Operators?
more detai... | Although Qmechanics's answer is formally complete and correct, there is a more intuitive formulation of this identity that makes it self evident. Consider the operator B which is A minus its expectation value in some state.
$$B = A - \langle A\rangle $$
Then the expectation value of B is zero in the same state (obviou... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/24178",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Proton-Neutron Lattice as a form of matter? Would it be possible for a lattice of protons and neutrons (I'm picturing a plane of hexagons in my head) to exist bound by the strong nuclear force (not gravity)? I know that the strong force losses its power when an atomic nucleus gets to be too large, but in a lattice, it ... | No, because the repulsive power of the protons accumulates toward infinity, blowing the structure apart. To accomplish what you have described you would need stable, negatively charged particles like antiprotons... which of course also fail in such an arrangement because they annihilate the protons!
The instability fro... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/24403",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 0
} |
The Difference between Thomas-Fermi Screening and Lindhard Screening Assuming the general theory of screening related to electron-electron interactions, I was wondering if anyone could provide a clear, yet conceptually complete explanation of the differences between the Thomas-Fermi and the Lindhard theories?
Following... | First, the Thomas-Fermi screening is a semiclassical static theory which assumes that the total potential $\phi(\mathbf{r})$ varies slowly in the scale of the Fermi length $l_{\text{F}}$, the chemical potential $\mu$ is constant and that $T$ is low. In principle, it does not rely on linear response theory.
The conditio... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/24460",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 1,
"answer_id": 0
} |
Ideal gas in a vessel: kinetic energy of particles hitting the vessel's wall Reading Landau's Statistical Physics Part (3rd Edition), I am trying to calculate the answer to Chapter 39, Problem 3.
You are supposed to calculate the total kinetic energy of the particles in an ideal gas hitting the wall of a vessel contain... | The reason your calculation is not right is because the mean energy of the molecules hitting the wall is not the mean number times the mean energy per molecule, because the fast molecules hit the walls more frequently than the slow ones.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/24595",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Possibility for radiation in dark matter that is not interactive with regular matter? Definition: Radiation in this case does not refer to electromagnetic radiation. It refers to any kind of emission of energy, even energy that does not interact with regular matter.
Just like dark matter does not interact with electro... | Well, I claim the answer is yes! Since the question defines radiation as emission of energy that doesn't interact with normal matter, I say that dark matter emitting dark matter particles qualifies as emission of energy that doesn't interact with normal matter. An clearly it can do that.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/24793",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 4,
"answer_id": 2
} |
Which is the strongest meteor shower expected in the next years in the Northern hemisphere? Which is the strongest meteor shower expected in the next years in the Northern hemisphere?
Is it possible to give good predictions for this?
| The Perseids in August are always good with 30+ meteors per hour. If you can get to a dark sky, you won't be disappointed. The Leonids hit their thirty-three year peak just a couple years ago so it will be a while before they peak again. The Perseids peaked in the mid-1990s (I saw 200 meteors in 1.5 hours through a hol... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/24859",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "12",
"answer_count": 3,
"answer_id": 2
} |
What objects look best in an O-III filter? I've heard that an O-III (Oxygen III) filter is great for planetary nebulae.
Is this true for all planetary nebulae, or just some or most?
What other target types are often improved with an O-III filter?
| Most planetary nebulae are improved with an O-III filter. I find it particularly helpful for the large dim Helix Nebula.
I also find it useful for most diffuse nebulae and supernova remnants, especially the Veil Nebula. For some reason, it doesn't help the Crab Nebula at all.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/24987",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
What is the current status of Pluto? Pluto has been designated a planet in our solar system for years (ever since it was discovered in the last century), but in 2006 it was demoted.
What caused this decision? And is there a chance that it could be reversed?
Edit: well, http://www.dailygalaxy.com/my_weblog/2017/03/nasas... | As many already said, Pluto is now considered a "dwarf planet"
For your second question, there is no chance that Pluto will be reclassified as a planet again.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25162",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "13",
"answer_count": 7,
"answer_id": 2
} |
Can any telescope be used for solar observing? Can any telescope, such as a 8" reflector, that is normally used at night to look at planets be used or adapted for solar observing?
What kind of adapters or filters are required or is it better to get a dedicated solar telescope?
I'd like to look at sunspots, flares, prom... | For viewing the moon I stopped down a 10" Newtonian reflector to 2", using tinfoil, thick paper, duct tape and a mason-jar ring (which is very round). I think this might also work for a projecting an image of the sun but with a much smaller aperture. The tinfoil cover with over the aperture, with its hole hopefully wi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25198",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 8,
"answer_id": 6
} |
What open-source n-body codes are available and what are their features? I'm interested in doing simulations with large numbers of particles and need a good n-body code. Are there any out there in the public domain that are open-source and what are their strengths and weaknesses. I'm interested in all types of codes,... | Amara Graps wrote a good overview of n-body simulation methods.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25241",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "19",
"answer_count": 3,
"answer_id": 1
} |
Video of Earth spinning? If the Earth is spinning or rotating at a really fast speed, why haven't we seen any videos from space of it spinning when we get a lot of photos of it?
| More importantly, in order to see the rotation properly, you'd need to stay at the same relative point in space. But in order to orbit the Earth, you typically need to go around it faster (until you get to geosynchronous orbit). The video's from the ISS make the Earth look like it's spinning because the ISS is orbiting... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25278",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 5,
"answer_id": 2
} |
What's the best way to start out with astrophotography on a tight budget? I'm new to astronomy and I don't have a great deal of cash to spend. I currently have a 3" reflector telescope which I've had great fun with. I also have a Pentax DSLR which I've been using to take long exposure photos of various constellations... | Without investing in a better telescope first I think a DIY webcam type setup or an entry level astrocam targeted at planetary use would probably be the best choice. A 3" reflector is unlikely to have a mount capable of tracking smoothly enough for long exposure; and the larger weight of a DSLR will cause more problem... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25319",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 2,
"answer_id": 1
} |
AGN accretion disk vs. torus The torus is the donut of dust encircling the Active Galactic nucleus. The accretion disk is inside the torus. Is there a boundary between the two? At what point does a torus become an accretion disk? What are their differences?
| If I understand the literature right, the disk "ends" when it reaches the self-gravity radius $R_{sg}$ where local gravity from the disk exceeds the vertical component of the black hole gravity and the disk becomes unstable. $$R_{sg}\approx 1680 \left[\frac{M_{BH}}{10^9 M_\odot}\right]^{-2/9} \alpha^{2/9} \left[\frac{L... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25365",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 1
} |
Color Variation in RR Lyrae I've been doing some research on RR Lyrae stars and haven't been really able to find an answer to this question.
RR Lyrae are well known for their periodic magnitude, and also are usually found in certain color ranges ("RR Lyrae Color Box"). My question is: does the color of RR Lyrae Stars (... | Although I'm a regular variable star observer, I don't observe RR Lyrae variables because they are not suitable targets for visual observers like myself. However, the long period Mira-type variable that I observe the most also change colour with brightness. At their dimmest, they look like glowing red coals, but they f... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25414",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Why did the WMAP mission last so much longer than Planck? NASA endorsed 9 years of data taken with the Wilkinson Microwave Anisotropy Probe (WMAP). The High Frequency Instrument aboard the Planck satellite ran out of coolant at the start of 2012, after about two and a half years of operation. Even if the Low Frequency ... | Dan Neely gave an excellent answer. I wanted to add that WMAP was initially planned as a one-year mission, and soon extended to two years---in which it reached its designed sensitivity goals.
After that point, it continued due to its success and the reasons listed by Dan.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25457",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 2,
"answer_id": 0
} |
The Sun as a gravitational lens Since the Sun is a gravitational lens with as focal length of 550 AU for visible light, with an immense amplification factor, shouldn't it light up objects hanging out there?
We should get solar sails up there to finally boost them somewhere interesting, opposite to the star that is emit... | How does 200 metre resolution at Alpha Centauri grab you?
http://www.cesr.fr/~pvb/gamma_wave_2005/presentations/optics/Koechlin.pdf
*
*Wherever in space there are intelligent creatures like us, they
will be driven to explore and understand our universe, just as we
do. We and they wish to see to the farthest depths ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25498",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 4,
"answer_id": 3
} |
What is behind the cosmological horizon barrier? I'm wondering what is behind the cosmological horizon barrier?
| Well - there are a couple of possibilities:
*
*Nothing: the universe could actually be the size we can see, with the edge about 46 billion light-years away
*Lots more universe, similar to what we can see
*An infinite universe
It doesn't really matter which, though, as nothing beyond that horizon can effect us or... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25585",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Why isn't sunset time in sync with solstice? The winter solstice in the Northern Hemisphere in 2011 is on December 22.
But if I look at the sunset times for a location such as Washington, DC on the USNO site, the sunset time starts reversing much earlier (around December 6th).
Shouldn't the sunset time start reversing ... | This is because the earth doesn't have a circular orbit, so some times the angular velocity of the earth is greater than average (and also the reverse). Perihelion is in early January, so the planets orbital velocity is greater (i.e. the Northern hemisphere winter is shorter than half a year long). So the affects the l... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25626",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 1,
"answer_id": 0
} |
If neutrinos travel faster than light, how much lead time would we have over detecting supernovas? In light of the recent story that neutrinos travel faster than photons, I realize the news about this is sensationalistic and many tests still remain, but let's ASSUME neutrinos are eventually proven to travel "60 ns fast... | The calculation is done for 1987A here. Basically, the neutrinos' fractional speed increase from the new paper is $2.48\pm0.28\pm0.30\times10^{-5}$ (statistical / systematic errors, respectively) . SN1987a was $166\,912\pm10.1$ ly away, so multiplying the fraction by the travel time gives $4.14\pm0.97$ years. In realit... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25670",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "12",
"answer_count": 3,
"answer_id": 0
} |
What was the apparent magnitude of the June 15th 2011 lunar eclipse? My plan was to observe and estimate the apparent magnitude of the Moon during totality of the June 2011 lunar eclipse, but the clouds rolled in at the exact moment, so I couldn't make any useful estimates. What was the apparent magnitude?
| I was on the wrong side of the planet to see this eclipse, but I would expect it was an extremely dark eclipse, because the Moon passed very close to the centre of the umbral shadow.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25749",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 2
} |
Can the Hubble telescope bring any star into focus? Lets say I am talking about a view like this supernova - 13 billions light year away. In short can Hubble bring any star into focus in the entire universe? And if so, to what definition?
I also wonder, how much time would time would it need to focus on a distant star... | Once a telescope is set in proper focus, objects at all distances are rendered into sharp images without any further changes in focus settings. However, the lowest luminosity of stars that can be observed does depend on distance. And the farther away a galaxy is, the less detail can be seen in its image.
Hubble can ima... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25829",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 4,
"answer_id": 2
} |
Where do the bipolar jets of black holes come from? How are they formed? And why are they so bright?
| Black holes are small relative to their mass, matter that falls into a black hole will accelerate to very high speeds and then get crammed into a very tight volume. If even a relatively modest amount of material is falling onto a black hole it will be bottlenecked like sand falling through the middle of an hourglass. T... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25875",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 1,
"answer_id": 0
} |
Why is a new moon not the same as a solar eclipse? Forgive the elementary nature of this question:
Because a new moon occurs when the moon is positioned between the earth and sun, doesn't this also mean that somewhere on the Earth, a solar eclipse (or partial eclipse) is happening?
What, then, is the difference between... | The Moon's orbit is inclined with respect to the Earth's orbit. In other words, if you imagine a Sun, Earth, and Moon model sitting on a tabletop, the Sun would sit approximately still and the Earth might slide around the desktop, while the Moon would orbit the Earth, hopping up off the table, and sinking back down in... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/25924",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "41",
"answer_count": 5,
"answer_id": 3
} |
How could I translate a field of view value into a magnification value? When I zoom in with Stellarium, it indicates a field of view (FOV) value in degrees, but most binoculars and telescopes are advertised with value like "nX magnification power."
How could I translate this value so I get an idea of what I will see wi... | Different telescope and binocular eyepieces have different fields of view, so that there is no direct relationship between magnification and field of view.
Eyepieces range in apparent field of view from 30° to 110°, typically being in the range of 50° to 70°. For any given eyepiece, you can calculate the actual field o... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26046",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 1
} |
Mass of a galaxy via luminosity Is there a general formula for calculating the mass of a galaxy, or even a nebula from the luminosity? Or, is there a way of calculating the total mass of a galaxy from its energy output?
Is there a Hertzsprung–Russell diagram equivalent for galaxies?
I know about gravitational lensing o... | It sounds like you already have a pretty comprehensive answer in hand, but I would mention that galactic clusters are often classified by the mass or luminosity of their Nth-biggest or brightest member, where N is a smallish integer like 5. The idea is that the biggest couple might be weird outliers, but by the time yo... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26136",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 2,
"answer_id": 0
} |
In astronomy what phenomena have theory predicted before observations? As far as I know, astronomy is generally an observational science. We see something and then try to explain why it is happening. The one exception that I know of is black holes: first it was thought of, then it was found.
Einstein's relativity is ... | The deflection of light by the sun was first predicted by Einstein's general relativity, then observed in a solar eclipse.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26177",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "17",
"answer_count": 10,
"answer_id": 8
} |
How to find the Andromeda galaxy without using a go-to telescope? In other words, what is the proper technique (star-hopping or other?) in order to find and properly point a telescope to this target? Would a star atlas or other tool/reference help? Can I use the R.A. and Dec. coordinates to find such deep-space objects... | Maybe I'm the only one who starts at Cassiopeia, but I find it easy to start in the appropriate "wedge" of Cassiopeia (with Schedar at it's point) and follow that towards the bright line of stars in Pegasus (Mirach, etc. ).
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26216",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 4,
"answer_id": 3
} |
Why are stars, planets and larger moons (approximately) spherical in shape (like, the Sun, the Moon, the Earth, and other planets)? Why are stars, planets and larger moons (approximately) spherical in shape (like, the Sun, the Moon, the Earth, and other planets)?
| Adding to the previous answer, consider the surface of the Earth. Any deviation from a spherical shape is either an indentation (canyon, valley) or a bump (hill, mountain). Any such deviation that's too big is smoothed out by gravity; a 100-kilometer mountain would collapse or sink, and a 100-kilometer deep valley wo... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26297",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "18",
"answer_count": 3,
"answer_id": 0
} |
What is exactly the density of a black hole and how can it be calculated? How do scientists calculate that density? What data do they have to calculate that?
| A black hole is a celestial body of extreme density and high gravitational pull that not reflect or emit radiation.
The process of forming a black hole is related to the evolution of some stars. As you know, a star of similar mass to the Sun ends up becoming a white dwarf, a small star with high density.
The explosion ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26515",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "23",
"answer_count": 6,
"answer_id": 4
} |
What is Hawking radiation and how does it cause a black hole to evaporate? My understanding is that Hawking radiation isn't really radiated from a black hole, but rather occurs when a particle anti-particle pair spontaneously pop into existence, and before they can annihilate each other, the antiparticle gets sucked in... | You sort of have the answer in your question - but you are assuming mass is positive, as opposed to viewing it as an amount of energy.
Since the particle that is emitted has positive energy, the particle that gets absorbed by the black hole has a negative energy relative to the outside universe. This results in the bla... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26605",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "24",
"answer_count": 6,
"answer_id": 0
} |
Why Aren't Saturn's Rings Clumping into Moons? While reading with my son about how a Mars-like planet collided with the early Earth that resulted in our current moon, it said the initial debris also formed a ring, but that ring ended up getting absorbed by the Earth and the Moon.
I couldn't answer his question then why... | The rings are too close to the planet.
There is a certain distance from planets called the Roche Limit. Moons can form outside of this limit, but inside, tidal forces are so great that they prevent particles from forming into moons under their own gravity. For instance, our moon is outside Earth's Roche Limit. Saturn's... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26643",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "20",
"answer_count": 2,
"answer_id": 1
} |
How much of the Earth would a spoonful of the Sun scorch? How much of the Earth would a spoonful of the Sun scorch if held at ground level?
I basically would like to conceptualize the heat of the Sun on a smaller scale, please.
| 10 million tons of neutrons burning at 15 million degrees it would be something similar to crater lake, ground zero would probably be glass, or a chunck of iron, at 15 million degrees it would instantly melt a city just with the flash. 1 teaspoon weighs 10 million tonnes(average mass of a star)it would be a textbook ex... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26690",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
What is this shadow of the Sun on the Moon? I was reading the article Moon Phases on HowStuffWorks. In the picture, each moon has a dark green area which represents the shadow of the Sun. How is this shadow formed and why is this important?
| The half of the Moon not represented by the dark green semicircle is directly illuminated by the Sun. The dark green half is away from the Sun, in solar "night." [Note that this does not mean that it is actually dark there, because the Earth casts a lot of light onto the surface of the Moon as well.] The light and dark... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26731",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Does a reference or classification standard for altitude classifications of geocentric orbits exist? I'm looking for a primary reference of the altitude classifications of geocentric orbits (LEO, MEO, GEO, HEO), but I was not able to find something so far.
I noticed that there is very different information about this c... | NASA's GCMD (Global Change Master Directory) has a classification of orbits which contains the following defintions (truncated for the altitude portion):
*
*LEO : Platforms that orbit between 80 km and 2000 km
*MEO : Platform orbits lie between 2000 km to 35,786 km, but most commonly at 20,200 km or 20,650, with an... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26776",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
Counting complete sets of mutually unbiased bases composed of stabilizer states Consider $N$ qubits. There are many complete sets of $2^N+1$ mutually unbiased bases formed exclusively of stabilizer states. How many?
Each complete set can be constructed as follows: partition the set of $4^N-1$ Pauli operators (excluding... | Here is an answer that should work. I do not currently have access to matlab to check this for anything other than the smallest cases, so you should do that.
First off, I find it easier personally to work in the reduced set of $3^N-1$ stabilizers for N qubits (generating the other from those). Entirely a personal prefe... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26805",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "16",
"answer_count": 2,
"answer_id": 0
} |
Values of SM parameters at one certain scale The general question is:
What are the values of Standard Model parameters (in the $\bar{MS}$ renormalization scheme) at some scale e.g. $m_{Z}$? As its parametrization in Yukawa matrices is not unique - what are the values of gauge couplings, fermion masses and CKM matrix?
T... | I think that the place to start for you is the Gfitter package. As I understand they have the best "global fit" of the SM parameters at $m_Z$.
Here is the recent paper which takes into account recently discovered God pa ..., sorry, the Higgs boson.
Also note that they've partially done your work by considering Type-II... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26849",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "19",
"answer_count": 2,
"answer_id": 0
} |
Literature on fractal properties of quasicrystals At the seminar where the talk was about quasicrystals, I mentioned that some results on their properties remind the fractals. The person who gave the talk was not too fluent in a rigor mathematics behind those properties, and I was not able to find any clues to this are... | Finally I asked the person working in this field and he gave me the paper http://prb.aps.org/abstract/PRB/v35/i3/p1020_1 where fractality of the spectrum is shown in rather reasonable model.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26918",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "19",
"answer_count": 2,
"answer_id": 1
} |
What are some ways to (approximately) symbolically diagonalize Hamiltonian operator? Specifically the Hamiltonian takes the form of
$$\hat H = \frac{\Delta }{2}{\hat \sigma _z} + {\omega _1}\hat a_1^\dagger {\hat a_1} + {\omega _2}\hat a_2^\dagger {\hat a_2} + {g_1}\left( {{{\hat a}_1}{{\hat \sigma }_ + } + \hat a_1^\d... | At least for $\omega_1=\omega_2$ it is possible to solve the system exactly. Our Hamiltonian can be written
$$\hat H = \frac{\Delta }{2}{\hat \sigma _z} + {\omega}(\hat a_1^\dagger {\hat a_1} + \hat a_2^\dagger {\hat a_2}) + ({g_1}{\hat a}_1+{g_2}{\hat a}_2){{\hat \sigma }_ + } + ({g_1}{\hat a}_1^\dagger+{g_2}{\hat a}_... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/26972",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 2,
"answer_id": 0
} |
Dual Pairs in Four Dimensions Following the conversation here, I am wondering if anyone knows of an example of dual pair with 4-dimensional N=1 SUSY which relates a non-Abelian gauge theory on one side to a theory with a Lagrangian description but no non-trivial gauge group. Cannot think of one off the top of my head, ... | This feels a little trivial, but I don't see why it isn't an example of what you want: Seiberg duality typically relates an $SU(N_c$) gauge theory with $N_f$ flavors to an $SU(N_f - N_c$) gauge theory. There are degenerate cases when $N_f - N_c = 1$ or $0$, which don't correspond to any dynamical gauge group in the inf... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27066",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 1,
"answer_id": 0
} |
Group of symmetries of Lagrange's equations Consider the following statements, for a classical system whose configuration space has dimension $d$:
*
*Lagrange equations admit a smaller group of "symmetries" (coordinate change under which equations are formally unchanged) than Hamilton's;
*The 'symplectic diffeomorf... | 0) Let us for simplicity assume that the Legendre transformation from Lagrangian to Hamiltonian formulation is regular.
1) The Lagrangian action $S_L[q]:=\int dt~L$ is invariant under the infinite-dimensional group of diffeomorphisms of the $n$-dimensional (generalized) position space $M$.
2) The Hamiltonian action $S_... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27122",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 2,
"answer_id": 1
} |
Examples of heterotic CFTs I'm trying to get a global idea of the world of conformal field theories.
Many authors restrict attention to CFTs where the algebras of left and right movers agree. I'd like to increase my intuition for the cases where that fails (i.e. heterotic CFTs).
What are the simplest models of heterot... | The first example that comes to mind is the heterotic string worldsheet theory, described in the original paper of Gross, Harvey, Martinec, & Rohm.
I don't know if there is a classification result for rational heterotic CFTs which generalizes the FRS result. However, if you want to understand the global space of CFTs,... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27172",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 2,
"answer_id": 0
} |
Is this a simple Lie algebra? This question comes from Georgi, Lie Alegbras in Particle Physics. Consider the algebra generated by $\sigma_a\otimes1$ and $\sigma_a\otimes \eta_1$ where $\sigma_a$ and $\eta_1$ are Pauli matrices (so $a=1,2,3$). He claims this is "semisimple, but not simple". To me, that means we should ... | In this relatively simple example, one can observe that the subalgebras $\{\sigma_a \otimes \frac{1\mp\eta_1}{2}\}$ are the two commuting copies of $su(2)$.
For more complicated situations, one actually has an algorithm to veify the simplicity of a Lie algebra. This is because (the root systems of) simple Lie algebras ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27217",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 2,
"answer_id": 1
} |
Quantum mechanics as classical field theory Can we view the normal, non-relativistic quantum mechanics as a classical fields?
I know, that one can derive the Schrödinger equation from the Lagrangian density
$${\cal L} ~=~ \frac{i\hbar}{2} (\psi^* \dot\psi - \dot\psi^* \psi) - \frac{\hbar^2}{2m}\nabla\psi^* \cdot \nabla... | You certainly couldn't recover quantum effects with a classical treatment of that Lagrangian. If you wanted to recover quantum mechanics from the field Lagrangian you've written, you could either restrict your focus to the single particle sector of Fock space or consider a worldline treatment. To read more about the ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27281",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "18",
"answer_count": 5,
"answer_id": 0
} |
Applications of the Feynman-Vernon Influence Functional I am looking for a reference where the Feynman-Vernon influence functional was defined and used in the context of relativistic quantum field theory. This functional is one method to describe non-equilibrium dynamics for open systems (e.g. coupled to noise) which s... | One of the avenues to search for an answer is the so-called Keldysh formalism which is used extensively in condensed matter, in particular in mescopic physics, to define and study steady-state and time-dependent quantum phenomena in systems with infinitely many degrees of freedom. A recent comprehensive review is given... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27315",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "17",
"answer_count": 2,
"answer_id": 0
} |
What are the justifying foundations of statistical mechanics without appealing to the ergodic hypothesis? This question was listed as one of the questions in the proposal (see here), and I didn't know the answer. I don't know the ethics on blatantly stealing such a question, so if it should be deleted or be changed to ... | I searched for "mixing" and didn't find it in other answers. But this is the key. Ergodicity is largely irrelevant, but mixing is the property that makes equilibrium statistical physics tick for many-particle systems. See, e.g., Sklar's Physics and Chance or Jaynes' papers on statistical physics.
The chaotic hypothesis... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27402",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "114",
"answer_count": 6,
"answer_id": 1
} |
Rigorous proof of Bohr-Sommerfeld quantization Bohr-Sommerfeld quantization provides an approximate recipe for recovering the spectrum of a quantum integrable system. Is there a mathematically rigorous explanation why this recipe works? In particular, I suppose it gives an exact description of the large quantum number ... | Contrarily to what is generally believed, a semiclassical approximation is achieved through two different series: One is WKB series and the other is the Wigner-Kirkwood series, the latter being a gradient expansion. In both cases, eigenvalues are obtained by the Bohr-Sommerfeld rule but just at the leading order. I hav... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27492",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "19",
"answer_count": 5,
"answer_id": 1
} |
Question from Schutz's In q. 22 in page 141, I am asked to show that if
$$U^{\alpha}\nabla_{\alpha} V^{\beta} = W^{\beta},$$
then
$$U^{\alpha}\nabla_{\alpha}V_{\beta}=W_{\beta}.$$
Here's what I have done:
$$V_{\beta}=g_{\beta \gamma} V^{\gamma},$$
so
$$U^{\alpha} \nabla_{\alpha} (g_{\beta \gamma} V^{\gamma})=U^{\alp... | The covariant derivative is metric compatible, so $\nabla_{\alpha} g_{\beta \gamma} = 0$. This is the condition that the inner product is preserved under parallel transport.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27625",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
How to write a paper in physics? I really like to do research in physics and like to calculate to see what happen. However, I really find it hard to write a paper, to explain the results I obtained and to put them in order. One of the reasons is the lack of my vocabulary.
*
*How do I write physics well? I think tha... | I will add, that nowadays the introductory part -and even the overall length of the paper- is more important that in classic times. This is because if you paper is too much specialist (and it will be) you must give the reviewers a hint that you have done your homework, that you known your field of study and that you ca... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27675",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "43",
"answer_count": 6,
"answer_id": 0
} |
Hilbert-Schmidt basis for many qubits - reference Every density matrix of $n$ qubits can be written in the following way
$$\hat{\rho}=\frac{1}{2^n}\sum_{i_1,i_2,\ldots,i_n=0}^3 t_{i_1i_2\ldots i_n} \hat{\sigma}_{i_1}\otimes\hat{\sigma}_{i_2}\otimes\ldots\otimes\hat{\sigma}_{i_n},$$
where $-1 \leq t_{i_1i_2\ldots i_n} \... | Claudio Altafini studies precisely this subject, in Tensor of coherences parameterization of multiqubit density operators for entanglement characterization and some follow-ups.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27719",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "14",
"answer_count": 3,
"answer_id": 1
} |
Electricity & Magnetism - Is an electric field infinite? The inverse square law for an electric field is:
$$
E = \frac{Q}{4\pi\varepsilon_{0}r^2}
$$
Here: $$\frac{Q}{\varepsilon_{0}}$$
is the source strength of the charge. It is the point charge divided by the vacuum permittivity or electric constant, I would like v... | It goes out forever, but the total energy it imparts is finite. The reason is that when things fall off as the square of the distance, the sum is finite. For example:
$$ \sum_n {1\over n^2} = {1\over 1} + {1\over 4} + {1\over 9} + {1\over 16} + {1\over 25} + ... = {\pi^2\over 6} $$
This sum has a finite limit. Likewise... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27820",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 0
} |
Producing photons with same frequency, different amplitude wave I don't understand how two photons of the same frequency can have different amplitudes, neither how to produce them.
I know that classically the square of the amplitude is proportional to the energy, but photons aren't classical particles.
My understanding... | Here is a simple calculation to think about. Imagine a generic radio transmitter emitting, say, 1 watt. That's 1 joule/second. Suppose the frequency is 100 MHz. Take the Einstein relation E=hf, where h is Planck's constant. Figure out the flux of photons (number emitted per second). To speak of photons in a QM sen... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27851",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 5,
"answer_id": 4
} |
How to determine n equidistant vectors from point P in three dimensions As an assignment for uni I need to figure out an algorithm that explodes a particle of mass $m$, velocity $v$, into $n$ pieces.
For the first part of the assignment, the particle has mass $m$, velocity of $0$, the particle explodes into 6 equal pie... | Interesting problem. Does the explosion need to be symmetric? For arbitrary $n$ I'm not sure this can be done. For $n$ = 6 just make the vectors point to the vertices of an octahedron.
If the explosion doesn't need to be symmetric I would generate $n$ - 1 random directions, speeds and masses, then add up the total mome... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/27990",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Given entanglement, why is it permissible to consider the quantum state of subsystems? Quantum entanglement is the norm, is it not? All that exists in reality is the wave function of the whole universe, true? So how come we can blithely talk about the quantum state of subsystems if everything is entangled? How is it ev... | It is true everything is entangled. However, in the many worlds interpretation, the wave function of the universe splits into many worlds. Typically, each decohered world taken by itself will be far less entangled than the wave function as a whole. While taking the partial trace to a subsystem can lead to a very mixed ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28048",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 8,
"answer_id": 6
} |
What kinds of materials contract the most in cold temperatures? I know that water expands in the freezer, but I'm curious about which materials contract in response to cold temperatures --- and most importantly, which ones undergo the most drastic changes?
| EDIT: I misread the question
I see you asked what kind of material contracts the most when you cool it. In this regard, hardly anything beats the ideal gas, whose contraction is about .1% per degree at room temperature. If you want a material, consider a bunch of balloons mushed together with drops of glue, or somethin... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28181",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 4,
"answer_id": 3
} |
Would you die if you put your hands on a powerline? You know how birds perch on powerlines without getting electrocuted? What if by some chance that I find myself falling and I grab on one of them? Let's say both of my hands are on the same line, would i get electrocuted?
I am thinking I won't because the current won't... | Have you seen the helicopter crews that work on overhead lines approach a live wire. They extend a conducting pole and equalize their voltage with the line. After than it is "safe" to work on the line. As long as there is a conductor connecting them to the wire it is ok. Of course the initial equalization process would... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28350",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 3,
"answer_id": 1
} |
Any noise slowly starting to take effects? I am studying a system subject to random noise, or a system driven by some noise, for example, heat flow or wave propagation perturbed by noise. I would like to know if there is a real system where the noise take effects slowly instead from the very beginning.
| It's not clear what you mean by "noise" but if you accept black-body radiation as electromagnetic noise then the average peak and total power output ramps up slowly for many systems including something as simple as a light bulb.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28425",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Example of diffusion process without a gradient A book I was reading stated that diffusion can exist without a gradient of a physical quantity. Heat is an example of diffusion because of temperature gradient and similar is the case of mass flow in chemistry. Can anyone give me an example for a gradient less diffusion p... | I would guess you mean self diffusion: see http://en.wikipedia.org/wiki/Self-diffusion for details.
Suppose you take an aqueous solution of (for example) salt that is uniform so there are no concentration gradients. There is no net diffusion, but the sodium and chloride ions wander around due to random thermal motion, ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28504",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
How does position uncertainty change in time? I have an online homework for my Modern Physics class, that requires me to find the uncertainty in velocity and position of a duck. The question is as below:
Suppose a duck lives in a universe in which h = 2π J · s. The duck has
a mass of 2.55 kg and is initially known t... | Following David Zaslavsky hint (see comments under question), I realized what I was doing wrong.
I was solving using
$$
\Delta(x) = \Delta(v).t
$$
This would give me
$$\Delta(x) = 0.47273$$
However, I wasn't taking into consideration the initial uncertainty in position.
Thus the correct was of doing it was,
$$\Delta(x)... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28685",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Derivation of the supergravity action in 11D The Einstein-Hilbert action of general relativity is uniquely determined by general covariance and the requirement that only second derivatives in the metric appear. Yang-Mills theory can be motivated in a similar way. In the original paper of Scherk, Julia, Cremer there are... | A beautifully conceptual derivation of 11d SuGra was given in
*
*Riccardo D'Auria, Pietro Fré, Geometric Supergravity in D=11 and its hidden supergroup, Nuclear Physics B201 (1982) 101-140 (nLab)
using the excellent supergeometric methods later laid out in their textbook
*
*Leonardo Castellani, Riccardo D'Auri... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28742",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
What is a "Center Of Mass" issue of a Gorillapod? I read somewhere that a Gorillapod may have "Center Of Mass" issues when used with the long lenses.
So, I wish to understand what is a "Center Of Mass" issue?
I have to clarify that I am NOT a physics student nor I ever intend to be. Answers in a layman's language woul... | Stand on your tiptoes and hold your hands out. You will discover what center of mass issues means. Basically gravity is pushing down on the camera/lens and it needs to be supported directly underneath where gravity is acting (center of gravity).
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28882",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 2
} |
Work done on charged particle by magnetic field in quantum mechanics Classically, we know from $\mathbf{F}=q\mathbf{v}\times \mathbf{B}$ that magnetic field does no work on a charged particle. In quantum mechanics, the Hamiltonian of a charged particle in a magnetic field is given by
$$\hat{H}~=~\frac{1}{2m} \left[\fr... | First, if the Hamiltonian is time-independent, and your Hamiltonian is assuming that $\vec A$ doesn't depend on time, then energy – the Hamiltonian itself – is conserved.
So what we mean by the magnetic field's doing no work is that the kinetic energy of the particle doesn't change i.e. the speed doesn't change. So one... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/28946",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
How can there be a quantum field theory that predicts all particle masses? Say I have a theory with only one (energy) scale, e.g. one given by the fundamental constants
$$\epsilon=\sqrt{\dfrac{\hbar c^5}{G}}.$$
In this case, where I can't compare to something else, is there a way to argue that
$$\epsilon<\epsilon^2<\e... | Here is my take on it from "history" point of view:
*
*With $c$ we understood that there is "no difference" between space and time and we started to use same units to measure them. Same thing for energy and momentum, magnetic and electric fields, e.t.c.
*Then $\hbar$ appeared and we realized that we could measure ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29058",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 4,
"answer_id": 3
} |
Why $\frac{d}{dt}r_{a}\nabla_{a}U_{ab}+\frac{d}{dt}r_{b}\nabla_{b}U_{ba}=\frac{d}{dt}U_{ab}?$ In classical mechanics for two mass particles $a$,$b$ we assume the symmetric potential arising from $F_{ab}$ and $F_{ab}$ given by $$U_{ab}(r)=-\int^{r}_{r_{0}}F_{ab}(r')dr'$$ and $$U_{ba}(r)=-\int^{r}_{r_{0}}F_{ba}(r')dr'$$ ... | Yes, the $r$-argument really is $r_{ik}:=|r_i-r_k|$, as he writes two pages earlier at the beginning of "Systeme von endlich vielen Teilchen". But then you don't need the force to show the relation, it's just the chain rule, which makes derivatives of $U$ into a two term expression and notice that $U(r_{ik})=U(|r_i-r_k... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29104",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
What is behind recoherence? I am quite familiar with the concept of decoherence, and I heard that a system that has decohered could recohere after that, I was wondering what could cause the the coherences that have leaked into the environment to come back to the system. I heard about thermal fluctuations for example, w... | The bold and brilliant pioneer Susskind came up with the causal patch conjecture. The universe is accelerating and will approach de Sitter space. The universe right up to the cosmological horizon is all that exists. Nothing beyond exists. The Hilbert space of the universe is finite in dimensionality, approximately $e^{... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29147",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 2,
"answer_id": 1
} |
Rotational speed of a discus I was wondering whether the rotational speed of a discus has any influence on the flight of the discus. Would slowing the rotation or speeding it up change the trajectory in any way or would the flight simply become unstable when slowing down?
| The faster it spins, the greater the aerodynamic side force on it; see Magnus effect.
Also, higher rotation increases the $\mu$ (ratio of edge speed relative to body to airspeed of the body) of the disc; the higher airspeed of the advancing edge relative to the retreating edge creates asymmetric lift & drag. The former... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29285",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 1
} |
Quasi 1D insulators with strong spin-orbital interaction We know that the spin-1 chain realizes the Haldane phase which is an example of
symmetry protected topological (SPT) phases (ie short-range entangled phases with symmetry). The Haldane phase is protected by the $SO(3)$ spin rotation symmetry.
If we change the sym... | I can provide an example for bosonic models.
\begin{eqnarray}
\mathcal{H} & = & \mathcal{K} + \mathcal{T}_\text{soc}
+\frac{U}{2}\sum_{i\tau} \hat n_{i\tau}( \hat n_{i\tau}-1) \nonumber \\
& & + U^{\prime} \sum_i \hat n_{i\uparrow} \hat n_{i\downarrow} + V\sum_{i\tau} \hat{n}_{i\tau}\hat... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29335",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "19",
"answer_count": 1,
"answer_id": 0
} |
Electrostatic Pressure Concept There was a Question bothering me.
I tried solving it But couldn't So I finally went up to my teacher asked him for help . He told me that there was a formula for Electrostatic pressure $\rightarrow$
$$\mbox{Pressure}= \frac{\sigma^2}{2\epsilon_0}$$
And we had just to multiply it to the ... | I think you can do this by dimensional analysis. I'll do the calculation because your professor almost certainly won't accept it, so it's not cheating :-)
We have the three quantities 1/$\epsilon_0$, $\sigma^2$ and $R^n$, where we don't know $n$, and the product has to have the dimensions of force. The dimensions are:
... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29504",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 6,
"answer_id": 2
} |
Rotationally invariant body and principal axis Suppose a rigid body is invariant under a rotation around an axis $\mathsf{A}$ by a given angle $0 \leq \alpha_0 < 2\pi$ (and also every multiple of $\alpha_0$).
Is it true that in this case the axis $\mathsf{A}$ is a principal axis of the rigid body?
If so, how to prove... | As a starting point, Wikipedia says on this issue:
The principal axes are often aligned with the object's symmetry axes. If a rigid body has an axis of symmetry of order $m$, meaning it is symmetrical under rotations of 360°/$m$ about the given axis, that axis is a principal axis. When , the rigid body is a symmetrica... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29614",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 3,
"answer_id": 0
} |
Gauge invariant but not gauge covariant regularization I'm not sure if someone's already asked this before, but I was wondering, in field theory,
*
*when we say that a certain field is gauge invariant but not gauge covariant, what does this mean? In particular, in Wikipedia, the regulator of Pauli-Villars is said t... | There are gauge conditions that are very useful but are not covariant. Working for example in Coulomb/Transverse gauge you can obtain gauge invariant results that are not manifestly covariant - this is called Gupta-Bleuler approach in QED. The BRS scheme is another example in non-Abelian gauge theories. In such situat... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29749",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "15",
"answer_count": 1,
"answer_id": 0
} |
Cosmic Background Radiation: How did planets form before the CBR could reach us? I've understood that the Cosmic Background Radiation(CBR) is an electromagnetic wave that originated from the big bang. However, we now live on a planet which that is also originating from the big bang.
Why does that Cosmic Background Radi... | The cosmic background radiation was always with us, it is not reaching us now. It just became cooler and cooler as time went on.
One has to understand that when we are talking big bang and general relativity we are talking of the universe starting from one (x,y,z,t) point and as time goes on, expanding. This means that... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29821",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Determine the acceleration and angular acceleration of a disc The question is:
A 90kg disc is floating in a frictionless vacuum. A 150N force is
applied to the outer rim of the disc. The disc has a radius of 0.25m
and a radius of gyration of 0.16m. What is the acceleration and
angular acceleration of this disc?... | There is only one force applied to the system $F = 150\,{\rm N}$ not two, $F_a$ and $F_\alpha$.
Then you have
*
*The total force applied equals the mass times the acceleration of the center of gravity.
*The total torque applied equals the mass moment of inertia (at the center of gravity) times the angular accelera... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29924",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Would the rate of ascent of an indestructible balloon increase as function of it's altitude? Assume a balloon filled with Hydrogen, fitted with a perfect valve, and capable of enduring vacuum (that is to say, it would retain it's shape and so well insulated that the extremes of temperature at high altitudes and in spac... | Short Answer: NO
Long Answer: the rate of ascent of a balloon is based on his bouyancy (the link mention a fluid, in this case the air), the bouyancy is independent is the gravity field, with density being the only variable.
$$m=\rho_fV_{\mathrm{disp}}$$
reference: wikipedia
with the law of ideal gas the can obtanin ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/29985",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 4,
"answer_id": 0
} |
How is external pressure transmitted when a fluid is not enclosed? Pascal's principle states that pressure applied to an enclosed fluid is transmitted undiminished to every part of the fluid.
How is the pressure transmitted in the case where the fluid is not enclosed?
For instance, pushing a block of wood to a beaker... | I'm not an expert in fluid physics, but after a bit of thought, I believe the following can give clues to your answer.
If the volume of fluid is not enclosed, it means any pressure applied to it that exceeds atmospheric pressure (as in, any amount at all by the block) will just make it flow to the parts of the beaker ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30085",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Show that Bell states cannot be decomposed as tensor products of single qubits' states I'm trying to learn about the Bell state $\frac{1}{\sqrt{2}}|00\rangle+\frac{1}{\sqrt{2}}|11\rangle$. Question 10.1 in Algorithms asks us to show that this cannot be decomposed into the tensor product of two single qubits' states.
It... | All you need to show is that there do not exist any $a,b,c$ or $d$ satisfying the conditions
$\frac{1}{\sqrt{2}}(|00\rangle)+|11\rangle)=(a|0\rangle+b|1\rangle)\otimes(c|0\rangle+d|1\rangle)$
and $|a|^2+|b|^2=|c|^2+|d|^2=1$.
You should be able to do this quite easily!
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30215",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Topology needed for Differential Geometry I am a physics undergrad, and need to study differential geometry ASAP to supplement my studies on solitons and instantons. How much topology do I need to know. I know some basic concepts reading from the Internet on topological spaces, connectedness, compactness, metric, quoti... | My favourite book is Charles Nash and Siddhartha Sen Topology and geometry for Physicists. It has been clearly, concisely written and gives an Intuitive picture over a more axiomatic and rigorous one.
For differential geometry take a look at Gauge field, Knots and Gravity by John Baez. Its very well written starts from... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30295",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 4,
"answer_id": 3
} |
Do the rings in Mass Effect's mass relays (2-axis gimbal) describe a stable rotation? Just out of curiosity. In the game Mass Effect, devices called mass relays contain two rotating rings, one inside of the other. See http://www.youtube.com/watch?v=qPxw5QjxhIs for an example, best seen around 00:10.
I was wondering: i... | According to Euler's rotation theorem, simultaneous rotation around more than one axis at the same time is impossible. If two rotations are forced at the same time, a new axis of rotation will appear. You can read more about this theorem over here: Wikipedia Link
Hope it helps.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30356",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 3,
"answer_id": 2
} |
Collision of a black hole & a white hole A black hole and white hole experience a direct collision.
What happens? What shall be the result of such a collision?
| A black hole pretty much is the same as a white hole.
Hawking's result proves they're essentially the same object, so the result will be a black hole with a radius larger than the sum of the radius of the black hole and the "white hole".
I'm just an undergraduate so possibly one of the other members can give a more d... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30406",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 8,
"answer_id": 1
} |
Number of bits needed to express physical laws? What is the minimum number of bits that would be needed to express a given physical law, like the law of universal gravitation? How many bits are needed to express each of the four fundamental forces? Is there a pattern here?
| One productive way of thinking of the complexity of physical laws is in terms of the Kolmogorov complexity of the algorithm that simulates a given physical situation. This is defined as the length of the shortest code which does the simulation.
If you are given a law of nature, like Newton's law of universal gravitatio... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30461",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
What are electromagnetic fields made of? I am trying to understand electromagnetic fields so I have two question related to them.
*
*What is a electromagnetic field made of? Is it made of photons / virtual photons?
*How about a static electric or magnetic field?
| Electromagnetic fields, which include static electric and magnetic fields, are indeed made of photons. From a particle physics perspective the Quantum Electrodynamics as a model of particles carrying electric charge interacting via photons has a spectacular agreement with experiment. The thing is, those experiments are... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30517",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "18",
"answer_count": 7,
"answer_id": 2
} |
Path traced out by a point While studying uniform circular motion at school, one of my friends asked a question:
"How do I prove that the path traced out by a particle such that an applied force of constant magnitude acts on it perpendicular to its velocity is a circle?" Our physics teacher said it was not exactly a v... | One can prove it in a more-or-less elementary way by solving a pair of simultaneous differential equations. In two dimensions, a vector that is perpendicular to a velocity $$\left(\begin{matrix}u(t)\cr v(t)\end{matrix}\right)\quad\mathrm{is}\quad\left(\begin{matrix}-v(t)\cr u(t)\end{matrix}\right).$$ The acceleration, ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30614",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 4,
"answer_id": 0
} |
Pressures Necessary for Carbon Detonation Carbon detonation is a characteristic event of Type 1a Supernova, where an accreting white dwarf near the Chandrashankar limit of 1.4 solar masses explodes, which is an extremely important standard candle for cosmology. An area of active research is designing computer simulatio... | I'm finding two differing definitions online.
In either case, I think that we can say that the full process is a thermonuclear explosion (and hotter, more energetic one than hydrogen/helium ones we use for bombs at that). That is scary bad.
The individual carbon-carbon fusion events can be simulated in a particle phys... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30755",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Why isn't it allowed to use a flash when taking pictures in a certain place? When I go to, for example, a museum I try to take some pictures.
Sometimes the museum staffs forbid me to use a flash. Do you know the reason? I don't think it is related to photo-electric effect, right?
| Yes, as you guessed it is related to the photoelectric effect. The photons from the flash, certain frequencies there, can change the molecular composition of the surface paints and pigments.
The precaution is the same as in avoiding a valuable painting or rug to be illuminated by the sun. It is the photoelectric effect... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30835",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 6,
"answer_id": 2
} |
What's the difference between Fermi Energy and Fermi Level? I'm a bit confused about the difference between these two concepts. According to Wikipedia the Fermi energy and Fermi level are closely related concepts. From my understanding, the Fermi energy is the highest occupied energy level of a system in absolute zero?... | If you consider a typical metal the highest energy band (i.e. the conduction band) is partially filled. The conduction band is effectively continuous, so thermal energy can excite electrons within this band leaving holes lower in the band.
At absolute zero there is no thermal energy, so electrons fill the band starting... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30922",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "33",
"answer_count": 5,
"answer_id": 0
} |
Capillaries in series The velocity of fluid of viscosity $\eta$ through a capillary of radius $r$ and length $l$ at a distance $x$ from the center of the capillary is given by; $v=\frac{P}{4l \eta }(r^2-x^2)$ (where $P$ is the pressure difference at the two ends of capillary). With the help of this I can find the rate ... | Assuming the fluids are incompressible, the flow through each capillary must be the same. Also the sum of the pressures across each capillary must equal the total pressure. Therefore, you have the equations:
$P_1+P_2 = P$
$V_1 = \frac{\pi P_1 r_1^4}{8 l_1\eta} = V_2 = \frac{\pi P_2 r_2^4}{8 l_2\eta}$
Solve this system ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/30980",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
What does spin 0 mean exactly? I heard two definitions:
*
*Spin 0 means that the particle has spherical symmetry, without any preferred axis.
*The spin value tells after which angle of rotation the wave function returns to itself: $2\pi$ / spin = angle. Therefore, spin 1/2 returns to itself after $4\pi$, spin 1 aft... | Spin zero just means scalar field quanta. No intrinsic angular momentum.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31119",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "22",
"answer_count": 4,
"answer_id": 3
} |
Coriolis Effect and the Space Shuttle The Coriolis effect is a well-known phenomenum, important in meteorology and ocean current forecasting. In addition to location (latitude), it depends on velocity and duration. I assume that commercial aircraft autopilot inertial guidence systems have the ability to compensate for ... | I am not an expert either, but I think the answer is still simpler than the one that James provided. First of all, the Coriolis effect is only mysterious if you think that your spot on the earth is stationary with respect to say, the sun. Once you acknowledge that a spot on the earth is moving you can take this into ac... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31161",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 2
} |
Dimension of vector resulting from tensorial product I'm quoting what I found in a book about quantum computation:
Individual state spaces of $n$ particles combine quantum mechanically through the tensor product. If $X$ and $Y$ are vectors, then their tensor product $X\otimes Y$ is also a vector, but its dimension is ... | OP's quote seems to originate from slide p. 45 in Dan Cristian Marinescu's keynote talk from the Computing Frontiers 2004 conference.
Individual state spaces of $n$ particles combine quantum mechanically through the tensor product. If $X$ and $Y$ are vectors, then their tensor product $X\otimes Y$ is also a vector, bu... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/31354",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 1
} |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.