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Author Topic: Are distant objects still receding at speed?  (Read 2170 times)

Terry Obeney

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Are distant objects still receding at speed?
« on: 23/10/2010 08:30:04 »
Terry Obeney  asked the Naked Scientists:
   
We're told that the galaxies farthest away are receding at the greatest speed. 

Surely, if we see the light from a galaxy 13 billion light years away, we are seeing it as it was 13 billion years ago. 

Thus, we only know that 13 billion years ago it was moving very much faster than objects which are today much closer and closer to the present time. 

Surely then we can only conclude that more distant objects were moving faster a long time ago and nearer objects are moving slower more recently.

This seems opposite to the conclusions from which Dark Energy is conjectured?

Terry in Dallas

What do you think?
« Last Edit: 23/10/2010 08:30:04 by _system »


 

Offline QuantumClue

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Are distant objects still receding at speed?
« Reply #1 on: 16/11/2010 15:38:40 »
This is a good question. I am not entirely sure how to allay the problems here. Let's try it bit by bit.

Surely, if we see the light from a galaxy 13 billion light years away, we are seeing it as it was 13 billion years ago.

Yes. True.

Thus, we only know that 13 billion years ago it was moving very much faster than objects which are today much closer and closer to the present time.

In a sense. The state we see that part of the universe in, was indeed the state it was in 13 billion years ago. Past and future are illusions though, according to quantum physics. Only stubbornly persistent illusions, in the words of Einstein.

Surely then we can only conclude that more distant objects were moving faster a long time ago and nearer objects are moving slower more recently.

I'd agree with this.

This seems opposite to the conclusions from which Dark Energy is conjectured?

Yes, I can see the quandry, and in my hopeful attempt to perhaps see an answer, I do not. It has somewhat surprised me your statement. I cannot seem to find an answer in myself.
 

Offline QuantumClue

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Are distant objects still receding at speed?
« Reply #2 on: 16/11/2010 15:42:09 »
I will forward the idea to an expert of cosmology for an answer.
 

Offline Pikaia

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Are distant objects still receding at speed?
« Reply #3 on: 16/11/2010 17:12:11 »
Thus, we only know that 13 billion years ago it was moving very much faster than objects which are today much closer and closer to the present time. 

Surely then we can only conclude that more distant objects were moving faster a long time ago and nearer objects are moving slower more recently.

The rate of recession of a galaxy depends on its distance, so a distant galaxy will always recede more quickly than a nearer galaxy.

We know from observation that the rate of expansion of the universe began to increase about 5 billion years ago; before then the expansion was slowing down. The "dark energy" is the mysterious cause of this acceleration. Since the expansion is accelerating, the most distant galaxies are receding from us and from each other at a greater rate than in the past.
 

Offline QuantumClue

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Are distant objects still receding at speed?
« Reply #4 on: 16/11/2010 18:28:34 »
Thus, we only know that 13 billion years ago it was moving very much faster than objects which are today much closer and closer to the present time. 

Surely then we can only conclude that more distant objects were moving faster a long time ago and nearer objects are moving slower more recently.

The rate of recession of a galaxy depends on its distance, so a distant galaxy will always recede more quickly than a nearer galaxy.

We know from observation that the rate of expansion of the universe began to increase about 5 billion years ago; before then the expansion was slowing down. The "dark energy" is the mysterious cause of this acceleration. Since the expansion is accelerating, the most distant galaxies are receding from us and from each other at a greater rate than in the past.

What is that law called again? I completely forgot about it.
 

Offline Pikaia

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Are distant objects still receding at speed?
« Reply #5 on: 16/11/2010 18:49:20 »
 

Offline QuantumClue

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Are distant objects still receding at speed?
« Reply #6 on: 16/11/2010 19:57:06 »
Do you mean Hubble's Law?

http://en.wikipedia.org/wiki/Hubble%27s_law

That's the one. Can anyone tell I haven't read up on cosmology in donks ;P
 

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Are distant objects still receding at speed?
« Reply #6 on: 16/11/2010 19:57:06 »

 

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