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telescopic viewing - visual time travel

 
 
jasonar
 
Reply Tue 15 Mar, 2005 01:00 pm
I'm having trouble grasping what most likely is a simple notion. The Hubble can pinpoint a galaxy in its infancy, possibly 12 billion years old, when fixed upon a specific point in space. Can one view the same galaxy at a more mature age, maybe at a state 6 billion years later? If so, how do astronomers keep up with which galaxies are newly discovered, and not the same galaxies previoulsy discovered, but at an older, mutated state? As well, if this is possible, how can you view an object through time without it leaving some kind of red-shift/blue shift trail? Is it possible to see the development of our own galaxy?
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Vengoropatubus
 
  1  
Reply Tue 15 Mar, 2005 01:51 pm
I believe you have the basic process wrong.
My understanding is this. Hubble sees a galaxy. To us, the galaxy is appears to be in its infant stages. If we had someone on the galaxy that we could converse with instantaneously, they would view the galaxy far differently. To them, it would likely be billions of years old.
I've never heard of any sort of physics process that would allow a galaxy to be viewed at many different points of its development outside of recording what's observed.
Red-shift/Blue-shift occurs only when an object moves through time.
I hope all of that was correct, but please correct me if I'm wrong.
One of the concepts that has confused me, is that if time stops advancing at the speed of light, why doesn't light move infinitely fast?
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Brandon9000
 
  1  
Reply Tue 15 Mar, 2005 02:33 pm
Vengoropatubus wrote:
One of the concepts that has confused me, is that if time stops advancing at the speed of light, why doesn't light move infinitely fast?

Your question contains an implicit misconception. No material object can be accelerated up to the speed of light, so any attempt to describe what happens if it does is meaningless.
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ebrown p
 
  1  
Reply Tue 15 Mar, 2005 02:50 pm
I am not sure if I understand the question, but I will take a shot...

The problem is that we use light to see... and light has a finite speed.

Let's say Thog is an alien astronomer looking at Earth from a planet 100 light years away, He is looking at you right now...

But there is a problem. Thog's telescope is pointed right at you, but the light that is bouncing off of you right now, won't reach Thog's telescope for 100 years.

The only way for Thog to see what you are doing right now is to point wait 100 years, and then point the telescope where you were right now. This way, the light which left you right now will just be arriving to enter his telescope to see you.

What Thog is looking at right now is light that left the Earth 100 years ago. Thus he is, in effect, looking into the past... since he sees "now" what happened 100 years in the past.

Likewise when we look at objects 100 light years away, we are seeing light that left 100 years ago. The images we see are of things as they were in the past.

When we look at things 1 billion light years away, we are seeing things as they were 1 billion years ago.

This rule is hard and fast. It is impossible to see what is happening now with things that are 1 billion light years away without waiting 1 billion years for the light to reach us.

Does this answer your question?
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Vengoropatubus
 
  1  
Reply Wed 16 Mar, 2005 12:23 pm
Brandon9000 wrote:
Vengoropatubus wrote:
One of the concepts that has confused me, is that if time stops advancing at the speed of light, why doesn't light move infinitely fast?

Your question contains an implicit misconception. No material object can be accelerated up to the speed of light, so any attempt to describe what happens if it does is meaningless.

The question isn't so much what would happen if an object with mass could be accelerated to the speed of light, but I thought that time stopping at the speed of light was part of one of the theories of relativity.
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ebrown p
 
  1  
Reply Wed 16 Mar, 2005 12:56 pm
Vengo, I think you are missing the main idea of relativity.

Time does not stop for you... ever, nor does it slow down. This means no matter what you do, you won't notice your watch won't go any slower and you wont detect any slowing of time no matter what you do).

Relativity means that things are relative to your perspective.

Let's take a situation and look at it from two perspectives. I hope this will be clear...

Let's say you and I on in spaceships. I look through a telescope and see you moving at 9/10 of the speed of light away from me. I am seated comfortably in my gally and my assumption is that my spaceship is not moving.

Time is normal for me within my spaceship. However, when I look at you through my telescope (through your window), I will notice the effects of relativity. I will see that time for you has slowed down. This means that when the minute hand on my clock moves 10 minutes, the minute hand I see in your spaceship through the window will have moved less minutes (less say 2 since I am too lazy to do the real math right now).

Here is the important part -- Your perspective of the same situation.....

You are also seated in your spaceship and you say I am wrong... You are seated comfortably in a spaceship that is not moving. It is I (according to you) that is moving away from you at 9/10 of the speed of light.

Time will be normal for you in your spaceship.

However, the same way I observe that time within your spaceship is going slower... you will observe that time within my spaceship is going slower. That is, when you look in your telescope through the window in my spaceship, you will notice that in the time it takes for your clock to advance 10 minutes, my clock only advances 2 minutes.

Here is the really important part -- We have two very different perspectives but both are equally correct....

It is clear that the distance between our spaceships is increasing-- but are you moving, or am I moving (or some combination of the two).

The answer is that there is no way to distinguish which is right. There is no experiment you can do to say that one perspective is better than the other.

In summary
Time never slows down for you-- ever. You will only see time slow down when you look at someone else who is moving relative to you. And even when you notice time slow down for another person, it is only your perspective. Time will not slow down for this person-- ever.





Time is normal for you within your spaceship.
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