Question About Moving Observers and Observable Universes

  • Thread starter MassNerd
  • Start date
  • Tags
    Observable
In summary, the three observers on three different planets see each other moving away from them faster than the speed of light, but they would be within each others particle horizon back then.
  • #1
MassNerd
1
0
[Mentor's Note: Post moved into its own thread from this one]

Hello, I have another newbie relativity question which is somewhat related to this topic. Here it is:

There are 3 observers on 3 different planets each in a different galaxy. Observer 1 stands on the north pole of their planet looking through a telescope looking straight up from the pole and see Observer 2 moving directly away at 51% the speed of light. Observer 1 then travels to the south pole and looks through a similar telescope looking straight up from that pole (the opposite direction of the first observation) and sees Observer 3 moving directly away at 51% the speed of light.

Ignoring there's a planet directly between Observer 2 & 3, could Observer 2 & 3 see each other? Or are they outside each other's observable universe? It would seem from Observer 1's point of view that they are moving away from each other faster than the speed of light.
 
Last edited by a moderator:
Space news on Phys.org
  • #2
MassNerd said:
Ignoring there's a planet directly between Observer 2 & 3, could Observer 2 & 3 see each other? Or are they outside each other's observable universe? It would seem from Observer 1's point of view that they are moving away from each other faster than the speed of light.

The rate of separation of Observer 2 and Observer 3 when viewed from Observer 1's frame can indeed be greater than c. However, from Observer 2 or 3's frame, the other is moving away at about 0.81 c. See this page: http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/einvel2.html

So no, they would not be out of each others observable universe assuming that they are closer than several billion light-years to each other. Beyond that it gets...complicated.
 
  • Like
Likes MassNerd
  • #3
Let's break this down into manageable pieces. Observer 1 is stuck in the middle. Let's just call this one earth. Observer 2 is due north of observer 1 and has a proper recession velocity of .51c which corresponds to redshift of .595. and a proper distance now of 7347.5 Mly [assuming the 2013 Plank cosmological parameters]. A galaxy receeding due south in the opposite direction at a redshift of .595 also has a proper distance now of 7347.5 Mly. A galaxy with a proper distance now of 14695 Mly [obtained by adding together the proper distances now of galaxy 2 and 3 from galaxy 1]. would have a redshift of 1.516 and a proper recession velocity of 1.02c. So you see the proper distances now simply add up, but the recession velocities and reshifts do not. The proper recession velocity is not quite double, but, the redshift nearly triples. Of course, we already knew that recession velocity and redshift are not additive, You use SR to add up recession velocities .but .51v is so slow relative to light it very nearly does add up. You use GR for redshifts, and the rules are different. BTW the particle horizon of galaxy 2 and 3 had a radius then of 12554 Mly, but, keep in mind the proper distance back then betrween 2 and 3 was only 5841 Mly, not their current proper distance of 14695 Mly, so they were within each others particle horizon and could both see each other back then with a large enough telescope. This whole then and now business gets a little confusing. Jorrie's cosmological calculator will confirm the values I gave: http://www.einsteins-theory-of-relativity-4engineers.com/cosmocalc_2013.htm
 

FAQ: Question About Moving Observers and Observable Universes

1. What is the theory of moving observers and observable universes?

The theory of moving observers and observable universes is a concept in physics that explores the relationship between an observer's movement and the observable universe. It suggests that an observer's perception of the universe is affected by their relative motion and that there may be multiple observable universes for different observers.

2. How does the theory of relativity relate to moving observers and observable universes?

The theory of relativity is closely related to the theory of moving observers and observable universes. It is the foundation of this theory and explains how an observer's motion affects their perception of time and space. It also provides a mathematical framework for understanding how different observers may have different experiences of the same event.

3. Can moving observers and observable universes be tested or proven?

While the concept of moving observers and observable universes is based on scientific principles, it is currently a theoretical concept and has not been proven or tested. However, scientists continue to explore this topic and gather evidence through experiments and observations to support or disprove this theory.

4. Are there any practical applications of the theory of moving observers and observable universes?

At this time, there are no known practical applications of this theory. However, further research in this area could potentially lead to a better understanding of the universe and how it is perceived by different observers. This could have implications for our understanding of time, space, and the nature of reality.

5. How does the theory of moving observers and observable universes challenge our current understanding of the universe?

This theory challenges the traditional view of the universe as a fixed and objective reality. It suggests that our perception of the universe is subjective and influenced by our relative motion. This challenges the idea of a single, absolute reality and raises questions about the nature of time, space, and our place in the universe.

Back
Top