# The Naked Scientists Forum

### Author Topic: What is the speed of gravitational waves?  (Read 1596 times)

#### thedoc

• Sr. Member
• Posts: 511
• Thanked: 12 times
##### What is the speed of gravitational waves?
« on: 16/03/2016 04:50:01 »
Gravitational waves - as they are not part of the electromagnetic spectrum I guess that the speed is not necessarily the speed of light. If this is the case then what is the speed of gravitational waves?
What do you think?
« Last Edit: 12/04/2016 12:32:45 by chris »

#### evan_au

• Neilep Level Member
• Posts: 4131
• Thanked: 249 times
##### Re: What is the speed of graviational waves?
« Reply #1 on: 16/03/2016 09:26:55 »
We know experimentally that Gravitational Waves travel fairly close to the speed of light, based on the time they were detected at locations about 3000 miles apart. But you can't be sure with just 2 detectors. This should be able to be confirmed with more precision when a third gravitational wave detector becomes operational, in a few years.

Note that the speed of electromagnetic radiation is not always "the speed of light". Light slows down when it enters denser materials; for example, light slows by about 40% when it enters your eyeball. Strictly speaking, electromagnetic radiation only travels at "the speed of light" through a vacuum.

This is covered in some detail in: http://www.thenakedscientists.com/forum/index.php?topic=65812.0

#### chris

• Neilep Level Member
• Posts: 5341
• Thanked: 65 times
• The Naked Scientist
##### Re: What is the speed of gravitational waves?
« Reply #2 on: 12/04/2016 12:34:20 »

That's an amazing statistic! Have you got a reference for that please Evan?

#### evan_au

• Neilep Level Member
• Posts: 4131
• Thanked: 249 times
##### Re: What is the speed of gravitational waves?
« Reply #3 on: 12/04/2016 19:00:39 »
Quote from: evan_au on 16/03/2016 09:26:55

That's an amazing statistic! Have you got a reference for that please Evan?
The speed of light is inversely proportional to the refractive index of the material through which it is passing.

A vacuum has a refractive index of 1, so light travels at c/1= "the speed of light in a vacuum" in a vacuum!

Air has a refractive index of 1.0003, so light travels at c/1.0003= pretty close to c in air!

The lens of a human eye has a refractive index of 1.386 - 1.406 (call it 1.4 = 40% more than a vacuum). Light slows to c/1.4 ≈ 214,000 km/s  when it enters the lens of your eye from the air.

See: https://en.wikipedia.org/wiki/List_of_refractive_indices

Oops! The refractive index of your lens is 40% higher than air, but when light enters your eyeball, the speed of light drops to 1/1.4=71% = 29% lower than air.
But when the light reflects back out of your cat's eyes at night, its speed will increase by 40% = 1/71%.

#### chris

• Neilep Level Member
• Posts: 5341
• Thanked: 65 times
• The Naked Scientist
##### Re: What is the speed of gravitational waves?
« Reply #4 on: 14/04/2016 19:08:20 »
the speed of light drops to 1/1.4=71% = 29% lower than air

That sounds more like it! Thanks.

#### Richard777

• Jr. Member
• Posts: 27
##### Re: What is the speed of gravitational waves?
« Reply #5 on: 17/04/2016 21:29:21 »

There may be an invariant velocity (vG).

Where; VG4 = G (the gravitational constant)

An object having mass (m) expends energy (EG) to deform the local continuum EG = mG1/2

Which may be written as; EG = mvG2

The energy value crops up everywhere, including within the Einstein gravitational constant (K).

This energy is associated with various forces.

One special force is Plank Unit force (FP0);  FP0 = EP02/hc

and  EP0= mPG1/2

Where; mP is Plank mass

I hope you find this interesting.

#### Colin2B

• Global Moderator
• Neilep Level Member
• Posts: 1921
• Thanked: 125 times
##### Re: What is the speed of gravitational waves?
« Reply #6 on: 18/04/2016 06:34:54 »
Where; VG4 = G (the gravitational constant)
I don't understand how you are balancing the dimensions of this equation

#### jeffreyH

• Global Moderator
• Neilep Level Member
• Posts: 3932
• Thanked: 55 times
• The graviton sucks
##### Re: What is the speed of gravitational waves?
« Reply #7 on: 18/04/2016 20:37:32 »
Where; VG4 = G (the gravitational constant)
I don't understand how you are balancing the dimensions of this equation

That's because he can't. There is no way that a velocity can be equal to the gravitational constant G. I have done some off the wall equations in my time but that one takes the cake.

The following users thanked this post: Richard777

#### Thebox

• Neilep Level Member
• Posts: 3164
• Thanked: 47 times
##### Re: What is the speed of gravitational waves?
« Reply #8 on: 18/04/2016 21:13:30 »
V (Gw)=0

#### The Naked Scientists Forum

##### Re: What is the speed of gravitational waves?
« Reply #8 on: 18/04/2016 21:13:30 »