Traveling at Near Speed of Light - Questions Answered

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Discussion Overview

The discussion revolves around the effects of traveling at speeds close to the speed of light, particularly regarding the blueshift and length contraction of the universe as perceived by an observer. Participants explore the implications of relativistic speeds in relation to the Cosmic Microwave Background (CMB) and the concept of reference frames.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that traveling at near light speed would result in the universe appearing blueshifted and length contracted, questioning why this is not observed currently.
  • Others reference the CMB and its role in determining the blueshift or redshift experienced by an observer, emphasizing the importance of the reference frame relative to the CMB.
  • A participant draws a parallel to the twin paradox, suggesting that acceleration plays a crucial role in understanding the differences in observations between inertial and non-inertial frames.
  • There is a discussion about the meaning of "relative to the CMB," with some clarifying that it refers to a frame where the CMB radiation exhibits no dipole anisotropy.
  • Some participants express confusion over the concept of reference frames and how they relate to the observed phenomena, particularly in the context of cosmic expansion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the implications of traveling at relativistic speeds, with multiple competing views on the role of reference frames and the effects of acceleration. The discussion remains unresolved regarding the exact nature of observations at such speeds.

Contextual Notes

Limitations include the dependence on definitions of reference frames, the unresolved nature of how acceleration affects observations, and the complexities surrounding the CMB's role in relativistic travel.

derek10
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Sorry if this was asked but I couldn't find a answer!
I heard that when you travel at near the speed of light (0.999...c, wrt the Earth or Sun maybe?) the universe would be seen blueshifted (even the CMB would be visible) and length contracted in front of you.
However I also heard that we are traveling right now to 0.9999...c wrt a reference frame. Why don't I see stars or CMB blueshifted or length contracted in front of me?
Many thanks!
 
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I may be wrong but this all appears paradoxical in the same manner as the twin paradox.
In the time dilation problem of twin paradox, the solution is that it is only the inertial observer on Earth who is qualified to apply time dilation. The moving twin aboard a rocket close to speed of light does not remain inertial at all times, for doing so would imply constant velocity and thus it would be impossible to return back to Earth - there must be some kind of acceleration involved.

See the section here http://www.einstein-online.info/spotlights/Twins titled 'turning the tables' and the subsequent section to see what's going on.
 
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Thanks for your reply
I don't understand what is "relative to the CMB", doesn't it travel at c?
Also do all galaxies share the same reference frame? (even when receding due to expansion?)
 
derek10 said:
Sorry if this was asked but I couldn't find a answer!
I heard that when you travel at near the speed of light (0.999...c, wrt the Earth or Sun maybe?) the universe would be seen blueshifted (even the CMB would be visible) and length contracted in front of you.
However I also heard that we are traveling right now to 0.9999...c wrt a reference frame. Why don't I see stars or CMB blueshifted or length contracted in front of me?
Many thanks!

We are traveling at .9999c wrt "a" reference frame, but we are not traveling that fast wrt the CMB's reference frame. It is how fast we travel wrt the CMB that matters for looking at blueshift/redshift of the CMB.
 
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Thanks Salford

So the key is the acceleration, right? As it is absolute and the galaxies and such do not, without accounting expansion as I accelerate to near c wrt the Earth so I would be like the twin who leaves it?
 
derek10 said:
I don't understand what is "relative to the CMB", doesn't it travel at c?
The phrase "relative to the CMB" is just shorthand for "the local reference frame where the CMB radiation has no dipole anisotropy".
 
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derek10 said:
Sorry if this was asked but I couldn't find a answer!
I heard that when you travel at near the speed of light (0.999...c, wrt the Earth or Sun maybe?) the universe would be seen blueshifted (even the CMB would be visible) and length contracted in front of you.
However I also heard that we are traveling right now to 0.9999...c wrt a reference frame. Why don't I see stars or CMB blueshifted or length contracted in front of me?
Many thanks!
The key to the whole issue is "wrt a reference frame." Which reference frame? The cmb's reference frame. You don't see the CMB blueshifted because you aren't traveling near c wrt its reference frame. Broader: all speed measurements are between two - any two - reference frames.
 
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thanks for your replies I think I am understanding now, so the CMB FoR is that which doesn't have any redshift or blueshift in any direction am I facing, right?

So can the CMB FoP be considered an "special" frame or is it just a regular one for this case?
 

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