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Author Topic: Does quantum mechanics (QM) require an absolute time frame?  (Read 2867 times)

Offline Bill S

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Somewhere, I no longer remember where, I read that QM requires a universal time that could be synchronized across the Universe.

Is this right? If so, why?
« Last Edit: 20/10/2015 00:33:29 by chris »


 

Offline Colin2B

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Re: Does QM require an absolute time frame?
« Reply #1 on: 19/10/2015 22:39:05 »
Never heard of that Bill.
 

Offline Bill S

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Quote from: Colin
Never heard of that Bill.

I seem to remember that in another "universe" it was you who said Pete was my best bet for an answer on that one. :)
 

Offline Thebox

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Somewhere, I no longer remember where, I read that QM requires a universal time that could be synchronized across the Universe.

Is this right? If so, why?

I thought ''light'' was synchronised across the universe? 

Space-time is synchronised being virtual?
 

Offline Colin2B

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Quote from: Colin
Never heard of that Bill.

I seem to remember that in another "universe" it was you who said Pete was my best bet for an answer on that one. :)
In that case you will have to wait for the U.S. to wake up as most of the hero members on this forum seem to be over there. Sorry Evan-au, I know there are quite a few Oz members here as well.
 

Offline lightarrow

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Somewhere, I no longer remember where, I read that QM requires a universal time that could be synchronized across the Universe.

Is this right? If so, why?

Non relativistic QM, that is, the first one that we study at university (and the only one in most cases) certainly requires an absolute time. For this reason Dirac and others in the '30 started to find a relativistic version of QM which then became QED and then QFT. No doubt that the "common" QM is inadequate to describe, for example, fast moving particles as in the accelerators.

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lightarrow
« Last Edit: 20/10/2015 18:31:08 by lightarrow »
 

Online jeffreyH

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Newtonian physics relies upon absolute time and absolute space, special and general relativity changed that. I am not experienced enough in quantum mechanics to comment on that but lightarrow seems to have covered it.
 

Offline Bill S

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Lightarrow, can that be taken as saying that originally QT had a universal time, but later "incarnations" introduced a relative aspect to time, so that there is no longer a universal time requirement?
 

Offline lightarrow

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Lightarrow, can that be taken as saying that originally QT had a universal time, but later "incarnations" introduced a relative aspect to time, so that there is no longer a universal time requirement?

Yes, in "relativistic quantum mechanics" only, however, not the common QM we find in the most common books. If it's not explicitly written "relativistic QM" then it's "non relativistic QM".

https://en.wikipedia.org/wiki/Relativistic_quantum_mechanics

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Space and time

In classical mechanics and non-relativistic QM, time is an absolute quantity: all observers and particles can always agree on, "ticking away" in the background independent of space. Thus in non-relativistic QM one has for a many particle system ψ(r1, r2, r3, ..., t, σ1, σ2, σ3...).

In relativistic mechanics, the spatial coordinates and coordinate time are not absolute; any two observers moving relative to each other can measure different locations and times of events. The position and time coordinates combine naturally into a four-dimensional spacetime position X = (ct, r) corresponding to events, and the energy and 3-momentum combine naturally into the four momentum P = (E/c, p) of a dynamic particle, as measured in some reference frame, change according to a Lorentz transformation as one measures in a different frame boosted and/or rotated relative the original frame in consideration. The derivative operators, and hence the energy and 3-momentum operators, are also non-invariant and change under Lorentz transformations.

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« Last Edit: 21/10/2015 17:46:23 by lightarrow »
 

Offline Bill S

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That can't possibly mean that the same scenario calculated using relativistic and non-relativistic QM would give different answers, and that they would both be right; or can it?
 

Offline lightarrow

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That can't possibly mean that the same scenario calculated using relativistic and non-relativistic QM would give different answers, and that they would both be right; or can it?
Certainly non-relativistic QM gives incorrect answers for particles' descriptions at relativistic speeds or however where relativity is required; I can't make specific examples because I'm not an expert.

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« Last Edit: 24/10/2015 12:38:28 by lightarrow »
 

Offline Colin2B

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That can't possibly mean that the same scenario calculated using relativistic and non-relativistic QM would give different answers, and that they would both be right; or can it?
Bill, that sounds the same as ordinary relativity vs non-relativity.
If we are considering ordinary Newtonian calculations eg sending rocket to moon, we would count the time here on earth and on moon as synchronised, it's only at relativistic speeds we need to do anything different. Must be same in QM.
 

Offline wolfekeeper

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I'm not sure whether you're talking about the Copenhagen interpretation of quantum mechanics.

In that interpretation, the wavefunction is said to collapse, and this collapse was(is?) thought to be faster than the speed of light, actually instantaneous.

If you think about it, that would give a 'preferred reference frame'. However, I'm not aware of any method to find this reference frame using quantum mechanics, so it's more of a theoretical issue than a practical one.

Incidentally, relativity doesn't disprove the existence of a reference frame, it just says you can't work out which one it is, at least using light or electromagnetic forces.
 

Online jeffreyH

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It's like asking where the centre of the universe is. Finding a preferred reference frame is not the only solution. Just find two points in the universe that are separated by distance but are equivalent. The equivalence can be found at the event horizons of black holes. Whatever the frame and whatever its motion light will behave in exactly the same way at the event horizon of each. A very impractical frame though due to the enormous distances involved.
 

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