A question on the rate of time in the Light we observe

In summary: However, there can be a different behaviour for objects that used to be closer than the Hubble distance, but moved by the expansion of the universe beyond it. These objects are no longer visible to us, so we cannot make any observations about them. In summary, the conversation discusses the effect of observed time on the light we see on Earth and how it relates to the expansion of the universe. It also touches on the Twin Paradox and the concept of cosmological time dilation. The Hubble distance, which is the point at which objects are receding at the speed of light, is also mentioned. It is noted that objects beyond this point are not observable and therefore cannot be studied.
  • #1
popfuzz
2
0
Hello everyone,
this is my first post, so if this question has been asked before please point me to the post to read an answer.

I was wondering if there is an effect on observed time that we observe from the light that we see on the earth. Also if there is an effect on time, is there a distance from
the Earth in the universe in which the universe is expanding at exactly the speed of light. And if this is the case are all observations beyond this point moving backwards in time?

Also if this is true does this shift in observed time have an effect on calculations that are made on the age of the universe and the rate at which the universe expands?

Thanks for your expert knowledge
 
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  • #2
Ok I was researching my own question a bit, i read about the Twin Paradox on wikapedia
http://en.wikipedia.org/wiki/Twin_paradox

Based on that, I should assume that light from farther distances is stretched (red shift) and that time is viewed at a slower rate. That is if I view an object that is near the edge of the viewable universe for a few years that I may be only viewing a few seconds in the life of that object. Am I correct in thinking that?

Also what is the effect of viewing objects that are past the distance in which the viewable universe is expanding faster then the speed of light? Has light been stretched to a point where time freezes? Or is the viewable light moving backwards in time?
 
  • #3
popfuzz said:
I was wondering if there is an effect on observed time that we observe from the light that we see on the earth.
Yes, this is called cosmological time dilation. This is a general relativistic effect for frames that are comoving with the expansion of space (frames that have no peculiar speeds). Special relativity is not applicable for cosmology, but only for situations where you can assume space-time to be static and flat. The cosmological time dilation factor is (1 + z) for a redshift z. You can read in Ned Wrights Cosmology FAQ:

This time dilation is a consequence of the standard interpretation of the redshift: a supernova that takes 20 days to decay will appear to take 40 days to decay when observed at redshift z=1.

popfuzz said:
Also if there is an effect on time, is there a distance from
the Earth in the universe in which the universe is expanding at exactly the speed of light.
This is the Hubble distance d = c / H. It is a consequence of the Hubble law v = H d that provides the recession speed v at distance d, with H the Hubble parameter. If you put c the speed of light and H = 71 km/s Mpc and convert units, you obtain d = 13,700 million light-years. Objects that are located today farther away are receding at speeds greater than c today. The redshift of the objects located at the Hubble distance is about z ~ 1.4.

popfuzz said:
And if this is the case are all observations beyond this point moving backwards in time?
You can see that there is no way to get negative time intervals with the time dilation factor I gave you above (the redshift z is always a positive value) and that there is no different behaviour between z < 1.4 and z > 1.4.
 
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FAQ: A question on the rate of time in the Light we observe

What is the concept of time dilation in the context of the speed of light?

According to Einstein's theory of relativity, time dilation refers to the phenomenon where time appears to pass at a slower rate for objects in motion, particularly at speeds close to the speed of light. This means that an observer on Earth would perceive time passing at a slower rate for a person traveling in a spacecraft at near the speed of light, compared to someone on Earth.

How does the speed of light affect the measurement of time?

The speed of light is a fundamental constant in the universe, and it plays a key role in the measurement of time. As an object's speed approaches the speed of light, time appears to slow down for that object relative to an observer. This phenomenon, known as time dilation, is a consequence of the laws of relativity and has been proven through various experiments.

Can we observe the effects of time dilation in everyday life?

Yes, we can observe the effects of time dilation in everyday life, but they are very small and not noticeable at everyday speeds. Time dilation is only significant at speeds close to the speed of light, which is much faster than anything we encounter in our daily lives. However, scientists have been able to measure and confirm the effects of time dilation through experiments involving atomic clocks and high-speed particles.

How does the rate of time appear to change as we approach the speed of light?

As an object's speed approaches the speed of light, time appears to slow down for that object. This means that the rate at which time passes for an object in motion will be slower compared to the rate of time for an observer at rest. This effect becomes more significant as the speed of the object approaches the speed of light.

Is the rate of time the same for all observers, regardless of their relative speeds?

No, the rate of time is not the same for all observers. According to Einstein's theory of relativity, the rate of time is relative and depends on the observer's frame of reference and their relative speed. This means that different observers may perceive time passing at different rates, depending on their relative speeds and positions.

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