Unifying Relativity and Quantum Mechanics: The Challenge of Planck Units

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Discussion Overview

The discussion centers on the nature of Planck units, particularly whether they are invariant across different frames of reference and the implications this has for the theory of relativity. Participants explore the relationship between Planck units, length contraction, and the potential need for modifications to relativity, including the concept of doubly-special relativity. The conversation touches on theoretical perspectives and the challenges of reconciling relativity with quantum mechanics.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants question whether Planck units are the same in all frames of reference and suggest that this could necessitate modifications to relativity.
  • There is a discussion about how length contraction might affect the measurement of Planck length in different frames, with some arguing that it would appear contracted in a moving frame.
  • One participant notes that if the contracted Planck length is shorter than the Planck length in their frame, it raises questions about how such a measurement could be made.
  • Another participant introduces the concept of doubly-special relativity as a potential framework for understanding these issues, referencing external sources for further reading.
  • Some contributions highlight that Planck units, while theoretically significant, may serve primarily as tools for mathematical calculations rather than definitive measures of physical reality.
  • There are references to speculative ideas in string theory and the notion that traditional concepts of space and time may not apply at scales smaller than the Planck scale.
  • One participant emphasizes the uncertainty surrounding these topics, noting that the conflict between relativity and quantum mechanics remains unresolved.

Areas of Agreement / Disagreement

Participants express differing views on the invariance of Planck units and the implications for relativity, indicating that multiple competing perspectives exist without a clear consensus.

Contextual Notes

Some claims rely on theoretical assumptions that may not be universally accepted, and the discussion acknowledges the speculative nature of certain theories, such as doubly-special relativity and string theory.

Andru10
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Are Planck units the same in all frames of reference ? If so, shouldn't the theory of relativity be modified to account for this ? (same as considering the speed of light the same in all reference frames) Because in it's current form, for a large enough velocity, through length contraction we can obtain a length shorter than the Planck length.
 
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Andru10 said:
Are Planck units the same in all frames of reference ? If so, shouldn't the theory of relativity be modified to account for this ? (same as considering the speed of light the same in all reference frames) Because in it's current form, for a large enough velocity, through length contraction we can obtain a length shorter than the Planck length.
Unless you are accelerating or deccelerating, you cannot determine if you are at rest or in motion relative to any other frame. Therefore, in your frame, regardless of your relative motion, Planck measures are the same as in any rest frame.

If you are talking about length contraction observed in a frame that is in motion relative to your frame, then Planck length would appear contracted in the frame that is moving relative to your frame.
 
Force1 said:
If you are talking about length contraction observed in a frame that is in motion relative to your frame, then Planck length would appear contracted in the frame that is moving relative to your frame.

And if the contracted Planck length (relative to my frame) is shorter than the Planck length (in my frame) how could I measure/observe it ?
According to wiki: Current theory suggests that one Planck length is the smallest distance or size about which anything can be known.
 
Andru10 said:
And if the contracted Planck length (relative to my frame) is shorter than the Planck length (in my frame) how could I measure/observe it ?
According to wiki: Current theory suggests that one Planck length is the smallest distance or size about which anything can be known.
I see what you are getting at.

Even though the derivation of the Planck measures represents them that way, they are really tools that enable us to do mathematical calculations about relationships. Then it depends on the theoretical perspective in which you are using the measures. GR will use them to define a universe in spacetime which is a point lattice geometry where you move from one point to another in Planck increments.

If you take that perspective and discuss the length contraction in a frame moving in relation to your frame then you are dealing with the relativistic conservation of momentum, i.e. special relativity.
 
Good question andru.
DSR is a neat idea to keep in mind but note that Wiki cautions:
The theory is highly speculative as of first publishing in 2002, as it relies on no experimental evidence so far.

Here are a few comments of Brian Green, THE FABRIC OF THE COSMOS:
(p 350)
If string theory is correct... the usual concepts of space and time simply don't apply on scales finer than the Planck scale. ..the concepts of space and time segue into notions for which "shrinking smaller" is as meaningless as asking "Is the number nine happy?"...

You can get a feel for this by checking out "T duality" in string theory...easy to understand in concept...

Things at sub Planck scales may be too energetic, too chaotic reflecting "quantum foam" jitters that jumbles everything together...

Utlimately the answer to your question is "we don't know": it's one manifestation of the conflict between relativity and quantum mechanics.
 
Naty1 said:
Good question andru.
DSR is a neat idea to keep in mind but note that Wiki cautions:

Here are a few comments of Brian Green, THE FABRIC OF THE COSMOS:
(p 350)


You can get a feel for this by checking out "T duality" in string theory...easy to understand in concept...

Things at sub Planck scales may be too energetic, too chaotic reflecting "quantum foam" jitters that jumbles everything together...

Utlimately the answer to your question is "we don't know": it's one manifestation of the conflict between relativity and quantum mechanics.

Thank you! This is very interesting. :smile:
 

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