# The Naked Scientists Forum

### Author Topic: Can space expand at greater than the speed of light?  (Read 2505 times)

#### Alan McDougall

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##### Can space expand at greater than the speed of light?
« on: 29/06/2008 09:59:29 »

Two object at different ends of the universe diameter (assuming it has a diameter) with the universe expansion at 5.8 red shift would result in them moving away from each other at a rate greater than the speed of light. What I mean is that objects are embedded in space which can expand faster than light, due it having zero mass.

Is this possible?

Alan

#### DoctorBeaver

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##### Can space expand at greater than the speed of light?
« Reply #1 on: 29/06/2008 20:45:47 »
Yes, that is exactly how it works - sort of.

As it is the space between them that is expanding, neither object need actually be moving in space. That means c is not an obstacle.

Take the example of 3 objects in a line. Call them A,B & C. B is in the middle. The space between A & B is expanding at a rate that causes them to move apart at 0.6c. Let's say the situation is the same for objects B & C. That means A & C are receding from each other at 1.2c as expansion is cumulative, unlike objects travelling at relativistic speeds.

It is actually surprisingly easy to calculate how far apart 2 objects must be for their speed of recession to exceed c; so let's put some figures to it.

First, you need the Hubble constant, which is approximately equal to 0.007% per million years. In other words, every million years, all distances in the universe expand by 0.007%. Put another way, the apparent speed at which 2 objects move apart increases by 71 kilometers per second for every megaparsec of distance between them.

The speed of light is approximately 300,000 kilometers per second, so we can calculate that the two objects must be separated by around 130,000 million million million kilometres for their speed of recession to exceed c. If you're really clever, you can calculate what that distance is in light years (calculating quickly on my fingers & toes, I make it about 13.7 billion).
« Last Edit: 29/06/2008 20:51:08 by DoctorBeaver »

#### Alan McDougall

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##### Can space expand at greater than the speed of light?
« Reply #2 on: 30/06/2008 07:47:04 »
Thank you Doc,

You cleared that up nicely.

Quote
The speed of light is approximately 300,000 kilometers per second, so we can calculate that the two objects must be separated by around 130,000 million million million kilometres for their speed of recession to exceed c. If you're really clever, you can calculate what that distance is in light years (calculating quickly on my fingers & toes, I make it about 13.7 billion).

Some quasars are estimated at 14.8 billion light years. I really

need those fingers and toes of yours

Alan

#### DoctorBeaver

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##### Can space expand at greater than the speed of light?
« Reply #3 on: 01/07/2008 19:30:37 »

Some quasars are estimated at 14.8 billion light years.

That would imply my calculation is wrong

#### Alan McDougall

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##### Can space expand at greater than the speed of light?
« Reply #4 on: 02/07/2008 02:52:16 »
I was not implying that your calculations were incorrect. The 14.8 billion light year estimate comes from another source.

Be a little more patient guys and less sensitive

#### DoctorBeaver

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##### Can space expand at greater than the speed of light?
« Reply #5 on: 02/07/2008 07:38:10 »
No. It's me. I'm wrong. I'm worthless. I think I'll go & eat worms.

« Last Edit: 02/07/2008 07:40:13 by DoctorBeaver »

#### Alan McDougall

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##### Can space expand at greater than the speed of light?
« Reply #6 on: 02/07/2008 08:51:49 »
The 14.8 billion separation would, therefore mean, these objects would be expanding much faster than C.

Expansion of the universe must occur and accelerate much  quicker at the much less massive "area" of the ancient early quasars epoch. (I use area for lack of a better word)

And expand less by being held by the greater mass of the younger epoch "area" we inhabit.

I appreciate your tears and loving kindness it makes my old grey heart glow!! man glow!!

Love

Alan

#### The Naked Scientists Forum

##### Can space expand at greater than the speed of light?
« Reply #6 on: 02/07/2008 08:51:49 »