# Gravitational Dissipation

1. Apr 27, 2007

### stripes

This isn't really a "homework" question, this is just a question that a friend and I came up with a few months ago. I'm currently in grade 11 taking physics 11 honours, and far above the rest of my class

Let's just say, IF the sun teleported instantaneously to a far away place in the unverse, in a way such that there is no less matter in the universe at any time, the amount of matter in the universe always remains the same. How long would it for the gravitational field that the sun had to dissipate. How long would the Earth stay in orbit for? Would it be 8.3 minutes (same as Speed of Light in a Vacuum)? Would it be instantaneous? Basically what I'm TRYING to ask is, how "fast" does gravity "move"?

2. Apr 27, 2007

### denverdoc

Do you suppose any field including a gravitational one could buck the speed of light? Fields have velocity and momentum.

3. Apr 27, 2007

### Mentz114

Gravitational waves, it is supposed, travel at the speed of light. Special relativity tells us that no signal can exceed the speed of light in vacuum.

4. Apr 27, 2007

### stripes

Well, I understand how gravity can have velocity, but how does it have momentum if it is not matter? How can it have a tendancy to move in a certain direction? This obviously wouldn't be found with p = mv, nor could it be found with p = hv/c, as that is for photons. Also, from what I've heard, there have supposedly been times where Alain Haché sent pulses at a group velocity of three times the speed of light. It has been possible to also make the group velocity of a laser beam travel at nearly 300 times c through caesium atoms.

5. Apr 27, 2007

### denverdoc

And from Mentz posted, whether waves or particles associated with gravity have momenta. What would be interesting is that there is a peculiar discrepancy in our world where charge comes in two flavors and can either exert or repel, and in motion create magnetism. Whereas mass is always attractional and so far as I know it, does not exert an additional force in motion, except whatever ripples thru space-time might exist. I don't pretend to know the answer to such, maybe someone else can help.

Binary system of stars ($\alpha$ - centauri) Mar 10, 2018