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Name: Stephen H.
Status: educator
Age: 20s
Location: N/A
Country: N/A
Date: 2001-2002


Question:
In theory, would time pass for an object that exists at absolute zero temperature? If, according to the theory of relativity, time only exists as it relates to motion, does that mean that if there is no molecular motion, time essentially would be at a standstill?


Replies:
Stephen,

Even at absolute zero there is motion. It is just that all the matter is in its lowest vibrational state and therefore cannot lose energy to its environment. Hence it is as cold as it can get which makes it an excellent reference point for temperature (and thus energy).

Since motion is not stopped at absolute zero, neither is time.

Greg Bradburn

P.S. What does it mean to say that motion has stopped? Motion of an object is always measured relative to the position of another object. Thus, while an object may appear to be motionless to a person in the same frame of reference in reality it may be speeding along at thousands of miles per second (when viewed from another frame of reference).


The concept of absolute zero temperature appears to surround itself in a cloak of mystery. Some deserved others not. Certainly the quantum effects of Bose-Einstein condensates are strange and only occur at temperatures less than micro-kelvins. Being able to trap light and make it "stop" certainly is not standard behavior, but it also is not magic and while extraordinary does not mean that our view of the molecular world requires major overhaul.

Even at absolute zero, which is not actually attainable even though you can get very close, not all motion ceases. Quantum mechanics still leaves us with zero point energy, which is related to the Heisenberg uncertainty principle.

There is no evidence that time would "stop" and it is not even clear what that means. The theory of relativity says that space and time are not separable, but it does not mean that it does not exist in various frames of reference.

Vince Calder


Stephen,

If the entire universe, everything that in any way could interact with anything else, never changed in any way, then you would not be able to detect passage of time. Even a molecule at absolute zero may detect random photons flying through the air, an occasional stray electron. A neutron at absolute zero still may be able to undergo beta decay, turning into a proton, electron, and neutrino. To measure time, something you can detect must be moving. You need to measure a change, and know at what rate the change occurs. This will allow you to make a time measurement. You do not need to move. Your clock needs to have something moving.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College


Good question! However, I believe that time would continue. It would be impossible (energy is conserved) to get the entire universe to absolute zero, so time would go on in some places, at least. Time stopping in only parts of the universe would be even more discombobulating than time stopping everywhere.

Also, even at absolute zero, some motion is necessary (zero-point energy) by Heisenberg's Uncertainty Principle. Since the uncertainty in a particle's position times the uncertainty in its momentum must be greater than Planck's constant, if a particle is constrained in its position at all, it's momentum must have some uncertainty, which means it cannot be zero. For example, electrons in atoms must still move in their orbits.

Best, Dick J. Plano ...



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