Absolute zero is interesting, especially where matter shows quantum effects like Bose-Einstein condensate and superconductivity.
Actually, Bose Einstein Condensation (BEC) and superconductivity occur at temperature higher than 0 kelvin (absolute zero). In superconductivity, the temperature of occurrence (critical temperature) can be over 100 kelvin.
The lowest temperature ever measured is 38 picokelvin (1E-9 or 0.000000038). It was measured in a BEC experiment. To put that in perspective, today’s quantum computers work at 10’s of millikelvin (1E12 or 0.01).
I’m no theorist, so I have always had questions about whether 0 kelvin is possible. Quantum mechanically, I can see how a state of <0> kelvin (probabilistic expectation of 0) can be achieved for a quantum state like a BEC, but don’t see how the value 0 can be observed.
Also, I’ve wondered: In a superconductor (at least, in a BCS superconductor) pairs are created through the interaction of electrons with phonons. Phonons are quantized vibrations of the atomic lattice of the material. If one could achieve absolute zero temperature, since temperature is a measure of the motion of the atoms, at zero there should be no motion of the atoms, therefore no lattice vibrations. So can superconductivity exist at absolute zero?
TLDR - BEC and superconductivity have nothing to do with Absolute Zero
Strictly speaking, it’s possible that one of the three neutrino masses is actually zero. What we know is that the differences between the masses are nonzero (or rather, strictly speaking, the differences between the squares of the masses), but the mass of the lightest neutrino could be anything. Personally, I’d be a bit surprised if the lightest one were massless. But not too surprised, because it’s not all that different from having several electroweak carrier bosons, only one of which is massless (the massless photon, and the massive Z and Ws).
That depends on the kind of quantity. With charge, for instance, you can have something with the charge of an electron, and you can have something with no charge at all, but you can’t have something with a charge anywhere in between those (at least, not any free particle: Quarks are in between, but never found except in combinations with integer charge). Similarly (but somewhat more complicated), you can have something with zero angular momentum, but never anything with nonzero angular momentum less than \frac{\hbar}{2}.
On the other hand, though, there’s no known or seriously hypothesized lower limit for energy, or velocity. To the best of our knowledge, those could be as low as you’d like.
So I have a stupid question: Is it possible that the absolute rate of flow-of-information is very slightly greater than c. Then you could calculate time dilation for a photon. That might change our cosmological understanding of red shift.
C is literally defined as the greatest speed at which information can be transferred.
But to answer the question I think you meant to ask: It is possible that photons might have some incredibly tiny but nonzero mass. IIRC, the current upper bound is somewhere in the vicinity of a millionth of an electron-volt. If that’s the case, then the speed of light would indeed be slightly less than c (how much less would depend on the energy of the light in question). It wouldn’t change what we know about the Universe very much, though (indeed, if it did change what we know about the Universe much, we could use that to determine the mass).
What do you think would be the ramifications of photons with a nonzero mass with respect to the observed redshift of photons. As I understand it, from the perspective of a photon, when it’s created and when it changes to something else is exactly the same time. If that assumption isn’t exactly precise, maybe there is another reason light gets red-shifted after a couple billions years (our time). Thanks for listening.
Isn’t red shift just the doppler effect? Photons with mass would still be red shifted.
If sound waves get doppler shifted why should massed photons behave any differently?
Looking at wikipedia I see there are a few different sources of redshift. The redshift caused by the expansion of the universe is not a Doppler effect but the principle is similar in that the wavelength is getting stretched.
One concept that changes from maths to science, is that in the exam room, you get to write numbers, such as the weight of the apple, as an accurate number such as 134.54 grammes
But in the physics lab and any lab, you should be writing the measurement with an error margin and calculating accumulated error margins along with any calculations done. Well, until you are in engineering and the applied assumptions already include huge error margins so you are calculated maximum or minimum that is far from actual, just for safety…
So weights of Apple L minus Apple M might be zero , meaning within error margins of the measurement .or calculations used. This appears a possible meaning of what the OP is getting at… that even 0 can be 0 ± 10 grams ? Often measurement error is given as a percentage, but it should be converted to absolute before being used in calculations.
It would be interesting if photons have a mass we can’t detect yet. If that were the case, the universe might not be expanding quite as fast as we think, because part of the red shift observed might be due to the passage of time from the perspective of the photon.
I’m not sure I’m following you there. How does a photon experiencing time affect the red shift?
I just answered that: No ramifications. If there were ramifications, then we would have already used them to determine the photon mass.
I guess didn’t really understand this. I don’t know what you mean by “if it did change what we know about the Universe, we could use that to determine the mass”.
If a photon has some mass, time would pass from its perspective. Wouldn’t that lead to a very small loss of energy over billions of years, i.e. red shift?
No. Where are you imagining that the energy would go?
Fair question. I don’t really understand where the energy goes when photons are redshifted due to the expansion of the universe.
Wouldn’t light traveling less than C mess up Maxwell’s equations? I thought that the whole rationale of special relativity was that light travels at the same rate in every inertial reference frame, from whence derives the Lorenz contraction and the universal speed limit at that velocity which is universally constant.
Yes. If the photon has a mass, then the correct equations aren’t the Maxwell equations, but something with the mass in in, and which reduces to the Maxwell equations in the limit as the mass approaches zero. But since the mass is, at least, very close to zero, Maxwell’s equations are at least very close to correct.
Was that a duck, or a goose?