# The Naked Scientists Forum

### Author Topic: Feedback: Expanding universe does not change the speed of light  (Read 1203 times)

#### thedoc

• Sr. Member
• Posts: 511
• Thanked: 12 times
##### Feedback: Expanding universe does not change the speed of light
« on: 13/03/2014 12:30:01 »
Jordan Munroe asked the Naked Scientists:

No, the expansion of the universe does not change the speed of light. If that were so, there would be a detectable change within a few decades.

When objects like galaxies expand away from us they are not actually moving through space and so relativity does not play a part. This is why two galaxies can be traveling away from each other at greater than the speed of light, a necessary consequence of an evenly expanding universe.

They are not necessarily moving away from each other there is just more and more space appearing between them. This is why I always argue that space has more to do with energy than distance. The space between two objects is simply the amount of energy required to bring them together.
What do you think?
« Last Edit: 13/03/2014 12:30:01 by _system »

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3920
• Thanked: 53 times
• The graviton sucks
##### Re: Feedback: Expanding universe does not change the speed of light
« Reply #1 on: 13/03/2014 15:34:18 »
This indicates that gravitational potential is the critical factor. However since the big bang gravity waves will necessarily have moved out into the void where no mass exists. A kind of gravitational shock wave for want of a better phrase. The total amount of gravitational potential within the universe should therefore be decreasing over time. This means less total gravitation within the radius enclosing the mass of the universe. The expansion could simply be a result of this overall decrease in internal gravitational potential. Then the energy required to bring masses together will increase over time.

#### jsmunroe

• First timers
• Posts: 2
##### Re: Feedback: Expanding universe does not change the speed of light
« Reply #2 on: 14/03/2014 12:49:25 »
What void? Do you mean higher dimensions or some "edge" to the universe?

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3920
• Thanked: 53 times
• The graviton sucks
##### Re: Feedback: Expanding universe does not change the speed of light
« Reply #3 on: 15/03/2014 18:50:30 »
What void? Do you mean higher dimensions or some "edge" to the universe?

All it means is that if gravitational waves propagate at c or close to it, when inflation ended after the big bang then gravitational waves would have outpaced the acceleration of matter.

#### Bill S

• Neilep Level Member
• Posts: 1826
• Thanked: 12 times
##### Re: Feedback: Expanding universe does not change the speed of light
« Reply #4 on: 15/03/2014 19:53:10 »
Quote from: jeffreyH
However since the big bang gravity waves will necessarily have moved out into the void where no mass exists.

Wouldn't this be the case only if the Universe is absolutely flat, finite and with a boundary?

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3920
• Thanked: 53 times
• The graviton sucks
##### Re: Feedback: Expanding universe does not change the speed of light
« Reply #5 on: 15/03/2014 20:48:26 »
Quote from: jeffreyH
However since the big bang gravity waves will necessarily have moved out into the void where no mass exists.

Wouldn't this be the case only if the Universe is absolutely flat, finite and with a boundary?

That depends upon whether this universe is the only universe. An expanding brane would accommodate this expansion of gravity waves until a collision with another brane interrupts it.

#### The Naked Scientists Forum

##### Re: Feedback: Expanding universe does not change the speed of light
« Reply #5 on: 15/03/2014 20:48:26 »