How Does the CMB Frame Differ from Other Frames in Relativity?

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Discussion Overview

The discussion revolves around the concept of the Cosmic Microwave Background (CMB) frame in the context of relativity, exploring its significance compared to other reference frames. Participants examine whether the CMB frame can be considered special or advantageous in understanding time and events, and how it relates to the notion of absolute time.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants propose that the CMB frame may provide a way to address the absence of absolute time in relativity, questioning how this might work.
  • Others challenge the comparison of the CMB frame to historical events, arguing that events occur in reality and not within specific frames, which are merely coordinate systems.
  • A participant notes that while the CMB frame simplifies calculations related to the universe's expansion, it remains a choice among many valid reference frames, and does not confer absolute status to time measurements.
  • There is a suggestion that the framing of questions about the CMB could be improved to clarify its significance relative to other frames.

Areas of Agreement / Disagreement

Participants express differing views on the significance of the CMB frame, with some asserting its utility while others emphasize that it does not provide absolute time. The discussion remains unresolved regarding the implications of using the CMB frame compared to other reference frames.

Contextual Notes

Participants highlight the limitations of using specific frames for events, noting that the choice of frame can affect the convenience of calculations without altering the underlying physics. There is an acknowledgment of the complexity involved in assigning coordinates to events.

palmer eldtrich
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As understand relativity there is no "absolute time" however I have its possible to use the CMb as a way round this? Is this right and how does it work?
 
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What makes the CMB frame more special than the frame where Lincoln was shot?
 
Vanadium 50 said:
What makes the CMB frame more special than the frame where Lincoln was shot?
Bad example, Lincoln being shot is an event which occurred in all frames. He was not not shot in the rest frame of the galactic center.
 
palmer eldtrich said:
As understand relativity there is no "absolute time" however I have its possible to use the CMb as a way round this? Is this right and how does it work?
The CMB does provide a valid choice of a reference frame. This choice of reference frame turns out to be very useful in that it simplifies the math for dealing with the expansion of the universe.

But it's still a choice: it's perfectly valid to select different reference frames. The math all still works in a different frame, and any physical calculation you do to predict an experimental result will come up with the exact same prediction.
 
Orodruin said:
an event which occurred in all frames

I don't understand this. An event doesn't occur in a frame. An event occurs in real life. A frame is how we assign coordinates to that event.
 
Vanadium 50 said:
I don't understand this. An event doesn't occur in a frame. An event occurs in real life. A frame is how we assign coordinates to that event.
The point is that regardless of how you assign coordinates, Lincoln was shot. This is an event which, as you say, did not occur in a frame. You seemed to want to assign events to frames since you were talking about the frame in which Lincoln was shot.
 
Orodruin said:
The point is that regardless of how you assign coordinates, Lincoln was shot. This is an event which, as you say, did not occur in a frame. You seemed to want to assign events to frames since you were talking about the frame in which Lincoln was shot.

So to make Vanadium50's point by rhetorical question, we need a different rhetorical question. How about "What makes the CMB frame more special than the frame in which the bullet that killed Lincoln was at rest?".
 
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palmer eldtrich said:
As understand relativity there is no "absolute time" however I have its possible to use the CMb as a way round this? Is this right and how does it work?
Not right.
There are some problems for which it is convenient to attach times to events using coordinates in which the CMB is isotropic, but that doesn't make those times any more "absolute" than any other. There are plenty of other problems for which those coordinates would be wildly inconvenient, and no problem in which the physics requires us to use them.
 
Nugatory said:
"What makes the CMB frame more special than the frame in which the bullet that killed Lincoln was at rest?".

Well, I was thinking about the frame where Lincoln was at rest, but we can make it the bullet.
 

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