Looks like some upset string theorists

[freespace]

Re: arts students: and only on Tuesdays and Thursdays, because that is all the contact hours they have!

[marki]

Don't I know it. They used to have a whole 6 hours per week contact when I would be slaving away in a lab half the night 5 days a week .

Mark

[Karls48 (Karl)]

Originally Posted by freespace

Fair points

We should also respect other people's right to work on what they find interesting - perhaps they believe understanding the origins of the universe is far more important than becoming a space faring species.

Cheers,
Steve

Yes they have right to do any kind of research they wish. But not if such research is funded by limited resources (public money) and does not produce any results that benefit society.

[renormalised (Carl)]

Originally Posted by marki

I was wondering how long it would take you to find this Carl .

Mark

I already knew this....I just stated it for the record

[sheeny (Al)]

Originally Posted by Solanum

Well, I know that if I don't get the results I expect the first thing I check is my instrumentation! However, one hopes that on things of this scale they are pretty sure they haven't stuffed up. I think it just rules out a pretty small subset of theories, as it limits the size of gravitational waves.

It would indeed be interesting if the don't find any. It's about time something in the standard model severely didn't work, give the theorists a bit more of a hard time!

Yeah I would assume they've checked their results and instrumentation, but you never know there's always the chance that even the checks haven't been successful.

It's an interesting subject to follow.

As I understand it, we should find gravitational waves eventually - we have evidence that they exist from energy loss of binary star, pulsar and black holes systems.

The really interesting thing I'm waiting for is the determination of the speed of transmission of gravity waves - and we can't do that until we can detect them directly. Now, I'm follower of scientific method and happy to be proven wrong... I'll follow the best evidence we have! ... but it strikes me we are currently working on trying to prove the unification of the forces. That is, that gravitation is of the same ilk as the other forces and therefore can only be transmitted at the speed of light.

Indulge me for a moment in a little thought experiment (or two). If gravitation (and gravitational waves) are transmitted at the speed of light, then how does a black hole continue to influence the space around it? Shouldn't the gravity / gravity waves / gravitons obey the event horizon just like light and everything else does? And if it did, shouldn't a black hole gravitationally "disconnect" from the rest of the universe when it forms?

Suppose, gravitation was transmitted faster than the speed of light, perhaps even instantaneously. Gravity / Gravity waves can then escape the event horizon of a black hole, which we observe (gravity is observed, that is, gravity waves we haven't detect yet).

Relax... don't jump to conclusions yet! Here comes thought experiment no 2... Suppose gravitation is transmitted faster than the speed of light - lets say instantaneously for simplicity and because we have no evidence to suggest an intermediate speed. What effect would the rest of the universe outside the observable universe have on the universe that we can see? Wouldn't the effect be similar to what we observe as "dark energy"?

All fanciful and ridiculous stuff, perhaps, but until we can detect and measure the characteristics of gravitational waves, we won't know. I've pondered these scenarios for a while now, and my hypothesis cannot be reality if gravity operates at the speed of light.

How can gravity exceed the speed of light? It can't be the same type of force as the EM and strong and weak nuclear forces. It would have to be a spacial effect on particles rather than a particle effect or characteristic. We know nothing can exceed the speed of light relative to space, but the expansion of space itself can exceed the speed of light. So a spacial effect could conceivably also act at speeds greater than the speed of light.

I have no evidence what so ever for the above hypothesis, but if some one can explain to me how gravity works across an event horizon, I'd be most grateful.

Al.

[marki]

Now this is interesting. If it works out it could mean the end of the dark matter/ dark energy fudge factor.

http://www.iceinspace.com.au/forum/s...ad.php?t=49074

Mark

[sjastro]

Indulge me for a moment in a little thought experiment (or two). If gravitation (and gravitational waves) are transmitted at the speed of light, then how does a black hole continue to influence the space around it? Shouldn't the gravity / gravity waves / gravitons obey the event horizon just like light and everything else does? And if it did, shouldn't a black hole gravitationally "disconnect" from the rest of the universe when it forms?

A gravitational wave doesn't move through space-time. A gravitational wave is space-time. It represents a change in space-time geometry around objects of rapidly changing mass. A gravitational wave doesn't travel through an event horizon. An event horizon is a potential energy barrier for particles traveling in space-time.

If gravitons do exist they would act as quantum mechanical carrier particles for gravity. As such the particle is created by an interaction between the black hole and the object. The end result is the gravitational force. The same principles apply to photons which are the carriers for the electromagnetic force.

It should be noted that gravity and gravitational waves are not the same animal. Masses effected by gravitational waves behave in a completely different way to gravity. The transverse effects of a gravitational wave can act as an attraction or repulsion force depending on the orientation of the masses relative to the wave.

Suppose, gravitation was transmitted faster than the speed of light, perhaps even instantaneously. Gravity / Gravity waves can then escape the event horizon of a black hole, which we observe (gravity is observed, that is, gravity waves we haven't detect yet).

Relax... don't jump to conclusions yet! Here comes thought experiment no 2... Suppose gravitation is transmitted faster than the speed of light - lets say instantaneously for simplicity and because we have no evidence to suggest an intermediate speed. What effect would the rest of the universe outside the observable universe have on the universe that we can see? Wouldn't the effect be similar to what we observe as "dark energy"?

If the gravitation is transmitted faster than light then information travels faster than light. This leads to all sorts of violations of causality such as observing events before they occur to simultaneous events occurring at "different times".

This can be explained by Minkowski space time diagrams.
http://en.wikipedia.org/wiki/Minkowski_diagram

Regards

Steven

[sheeny (Al)]

Originally Posted by sjastro

A gravitational wave doesn't move through space-time. A gravitational wave is space-time. It represents a change in space-time geometry around objects of rapidly changing mass. A gravitational wave doesn't travel through an event horizon. An event horizon is a potential energy barrier for particles traveling in space-time.

If gravitons do exist they would act as quantum mechanical carrier particles for gravity. As such the particle is created by an interaction between the black hole and the object. The end result is the gravitational force. The same principles apply to photons which are the carriers for the electromagnetic force.

It should be noted that gravity and gravitational waves are not the same animal. Masses effected by gravitational waves behave in a completely different way to gravity. The transverse effects of a gravitational wave can act as an attraction or repulsion force depending on the orientation of the masses relative to the wave.

Thanks for taking the time to read and reply Steve. I understand a gravitational wave appears as a variation in space time. And that may be the clue that sets it apart from the other forces. I'm just suggesting that as attractive as a unified theory of the forces is, assuming that gravity works by the same or similar mechanism to the EM and strong and weak nuclear forces could possibly be proved wrong in the fullness of time. We don't know enough yet.

Originally Posted by sjastro

If the gravitation is transmitted faster than light then information travels faster than light. This leads to all sorts of violations of causality such as observing events before they occur to simultaneous events occurring at "different times".

This can be explained by Minkowski space time diagrams.
http://en.wikipedia.org/wiki/Minkowski_diagram

Regards

Steven

This is very true. It is a strong nail in the coffin for my proposed hypothesis. It doesn't change the concept of causality (or the direction of time) but it would change the concept of simultaneity, just as we experience now with events we can both see and hear over a long distance.

But think further about what that means...

• it would mean that gravitational waves are exceedingly small (on the basis that neither matter nor energy can be created or destroyed and the inverse square law, so the most common G waves we would see would be from the movement of mass/energy only - I also imagine the speed of propagation would affect the amplitude of the wave for a given energy);
• it would mean that the gravitational waves from the big bang are already lost (perhaps not if the speed of gravitation happens to be finite);
• it would mean we could make some deductions about the universe outside what is visible.

Purely a thought experiment at this stage! Though I'm happy to be a "technical adviser" to anyone who wants to use the idea in a sci-fi series/movie/book.

Honestly, I expect we know more than I've been able to find / study / learn, so I'm just offering the concept here as thought fodder in the spirit of scientific method and hoping I'll learn something I don't know from the discussion.

Al.