Does momentum-energy produce gravitation?

[lemur]

First, is it valid that as an object gains momentum-energy, it also gains gravitational-mass? Second, if it does and you have very massive fast-moving object orbiting around a black hole, could the gravity stretch spacetime in a way that expands the black hole beyond its Schwarzschild radius?

 

edit: if nothing else, could it decrease the relative density of the black hole in a way that would increase its rate of Hawking radiation?

Edited February 23, 2011 by lemur

[Widdekind]

The mass stress-energy tensor incorporates information, about not only the mass density in space, but also the motions of that mass. Moving mass gravitates differently, than the same static.

[lemur]

The mass stress-energy tensor incorporates information, about not only the mass density in space, but also the motions of that mass. Moving mass gravitates differently, than the same static.

As I understand it, mass increases as objects approach C. So, theoretically if an object is moving very close to C its mass could increase and thus exert an amount of gravity much higher than it would in a relatively static state. So, in this sense, I don't see why a black hole with numerous satellites of very high mass couldn't be "out-gravitied" by those satellites. After all, gravity is a pattern of force vectors which seem to be able to cancel each other out, for example at lagrangian points and at the center of planets, etc. So why couldn't the gravity of a large amount of matter orbiting a black hole at very high speed not overpower the centripetal gravity of the black hole?

[DrRocket]

The mass stress-energy tensor incorporates information, about not only the mass density in space, but also the motions of that mass. Moving mass gravitates differently, than the same static.

 

This is not correct.

 

The stress energy tensor, like the curvature tensor to which it is equated by the Einstein field equations is invariant -- independent of the observer. Motion is not an invariant.

 

You cannot increase curvature by adopting a reference frame in motion with respect to your initial frame.

 

If what you are suggesting were true, light would see anything with non-zero rest mass as the source of a black hole. It would be really dark around here.

[lemur]

You cannot increase curvature by adopting a reference frame in motion with respect to your initial frame.

Wouldn't "increasing curvature" imply strengthening of the gravity well being orbited? I was thinking in terms of increasing curvature relative to the thing moving, or in relation to a gravity well, straightening of the curvature of the gravity well due to counter-curvature caused by the satellite and its motion.

Edited February 28, 2011 by lemur

[DrRocket]

Wouldn't "increasing curvature" imply strengthening of the gravity well being orbited?

 

Yes. The point is that you can't do that by adopting a reference frame in which an object is moving. The curvature will be the same as in the rest frame.

 

 

 

I was thinking in terms of increasing curvature relative to the thing moving, or in relation to a gravity well, straightening of the curvature of the gravity well due to counter-curvature caused by the satellite and its motion.

 

Motion won't help.

 

Counter-curvature ?

[lemur]

Counter-curvature ?

Yes, maybe there's another way to propose it: as an object approaches C, it takes increasing amounts of energy to accelerate it relatively less, right? So, for example, as an object orbiting a black hole approaches C, it doesn't accelerate to a higher orbit but continues at the same speed and altitude but with higher energy, right? So isn't that higher energy that it expresses at relativistic speeds similar to the propagation energy expressed by photons, which express mass only as momentum over spacetime? In other words, isn't energy through spacetime the same thing as gravitational mass? I.e. a photon or material object in motion expresses energy as mass to the extent that its speed approaches C? E.g. light expresses mass as energy moving at C, but material objects may express mass-gravitation AS WELL AS gravitation due to motion-energy according to their speed relative to C. This idea is making loads of sense to me, but maybe I need some clear explanation as to how its misguided.

[DrRocket]

Yes, maybe there's another way to propose it: as an object approaches C, it takes increasing amounts of energy to accelerate it relatively less, right? So, for example, as an object orbiting a black hole approaches C, it doesn't accelerate to a higher orbit but continues at the same speed and altitude but with higher energy, right? So isn't that higher energy that it expresses at relativistic speeds similar to the propagation energy expressed by photons, which express mass only as momentum over spacetime? In other words, isn't energy through spacetime the same thing as gravitational mass? I.e. a photon or material object in motion expresses energy as mass to the extent that its speed approaches C? E.g. light expresses mass as energy moving at C, but material objects may express mass-gravitation AS WELL AS gravitation due to motion-energy according to their speed relative to C. This idea is making loads of sense to me, but maybe I need some clear explanation as to how its misguided.

 

 

You seem to think that you are going to re-discover and understand general relativity by introspection. That was only marginally successful for Einstein, who needed a lot of outside expert help. You are not Einstein. Read a book.

[lemur]

You seem to think that you are going to re-discover and understand general relativity by introspection. That was only marginally successful for Einstein, who needed a lot of outside expert help. You are not Einstein. Read a book.

That's the first time I've ever read a post and saw a parallel with the user avatar. What's with the ad hominem attacking? What does it matter what Einstein was like or whether I think I'm Einstein, Moses, or Tiger Woods? Am I supposed to not post what I think because I might sound like I'm trying to be Einstein? It beckons the question who you think you are to attack me like that.

[Widdekind]

This is not correct.

 

According to Wikipedia, the Stress-Energy Tensor is -- that is not frame-dependent ? The article seems to say, that the form of the S.E.T. changes, in an inertial reference frame co-moving w/ the fluid.

[ajb]

According to Wikipedia, the Stress-Energy Tensor is -- that is not frame-dependent ? The article seems to say, that the form of the S.E.T. changes, in an inertial reference frame co-moving w/ the fluid.

 

 

That is frame dependent, but the beauty of using tensor fields on smooth manifolds is that any equation between tensor fields have exactly the same form in any frame. This means that for most things, it is ok to pick some coordinates suited to your problem and work there.

[lemur]

Is any of this going to directly address the OP at some point?

[swansont]

That's the first time I've ever read a post and saw a parallel with the user avatar. What's with the ad hominem attacking? What does it matter what Einstein was like or whether I think I'm Einstein, Moses, or Tiger Woods? Am I supposed to not post what I think because I might sound like I'm trying to be Einstein? It beckons the question who you think you are to attack me like that.

 

!

Moderator Note

1. Not all personal comments are ad hominem; that's a personal comment/attack used to rebut or justify not addressing an argument (example: you're ugly, therefore you're wrong, or you're just saying that because you're a druid)

2. Posting what you think, as a declaration (even if in question form) can cross over into speculation. So if what you are posting is proposing "alternative" science, the answer is no, you shouldn't just post what you think. This applies to Widdekind as well.

 

DrRocket answered the original question quite succinctly — you don't increase gravitation by moving. Also, mass is invariant — it doesn't increase with speed.

[lemur]

!

Moderator Note

1. Not all personal comments are ad hominem; that's a personal comment/attack used to rebut or justify not addressing an argument (example: you're ugly, therefore you're wrong, or you're just saying that because you're a druid)

2. Posting what you think, as a declaration (even if in question form) can cross over into speculation. So if what you are posting is proposing "alternative" science, the answer is no, you shouldn't just post what you think. This applies to Widdekind as well.

 

DrRocket answered the original question quite succinctly — you don't increase gravitation by moving. Also, mass is invariant — it doesn't increase with speed.

So comparing me negatively with Einstein is not the same thing as saying that I'm stupid therefore I'm wrong?

 

I wasn't just posting what I think, btw. I may be posting just what someone else thought, though, because I can't remember where I got the idea that energy can generate gravitation and why/how. Certainly people have posted that light influences spacetime curvature.

 

 

[swansont]

So comparing me negatively with Einstein is not the same thing as saying that I'm stupid therefore I'm wrong

 

I don't see it that way. I have to wonder in what universe saying you aren't on par with Einstein in the field of relativity is an insult, or means you're stupid. You probably aren't as rich as Bill Gates either. Does that make you poor?

 

The path isn't that you're stupid and therefore wrong. It's that the person who came up with this theory by thought took years to do it (and he also used math), so unless you are actually smarter than Einstein, the guesswork/speculation qualitative method isn't going to work. The advice to go read a book is right on target. The nature of the forums doesn't lend itself to conveying large amounts of information.

[lemur]

I don't see it that way. I have to wonder in what universe saying you aren't on par with Einstein in the field of relativity is an insult, or means you're stupid. You probably aren't as rich as Bill Gates either. Does that make you poor?

 

The path isn't that you're stupid and therefore wrong. It's that the person who came up with this theory by thought took years to do it (and he also used math), so unless you are actually smarter than Einstein, the guesswork/speculation qualitative method isn't going to work. The advice to go read a book is right on target. The nature of the forums doesn't lend itself to conveying large amounts of information.

The issue wasn't actually to compare me with Einstein. I have no desire to be compared with anyone. The issue was whether it was an ad hominem attack akin to calling me stupid. I don't think there was any other point to comparing me with Einstein except to say that unless I am on par with Einstein, I should shut up because I'm too stupid to be talking about the things I'm talking about. That's an ad hominem attack, isn't it? Why can't I think about physics qualitatively without understanding all the math? If something I say is blatantly misguided in light of math I don't understand, is it that hard to say so without insulting me? If someone then has the ability and interest in explaining my mistake in terms of the math in language I can understand, great for me. If they don't have the time or the patience at that moment or ever, that's understandable too. Imo, a discussion should be a set of non-mandatory opportunities to interact, learn, and explore ideas through discussion so you can say whatever you want or nothing at all to a post, but I don't see what's constructive about just telling someone to go away and read. Certainly I read on these topics anyway, so really it just comes across more as a polite suggestion to go away. Why is that necessary?

 

 

 

[SMF]

Lemur. This quote- "In reality, ad hominem is unrelated to sarcasm or personal abuse. Argumentum ad hominem is the logical fallacy of attempting to undermine a speaker's argument by attacking the speaker instead of addressing the argument" can be found here- http://plover.net/~bonds/adhominem.html

 

You can only communicate if you know the language. I suggest that you read the explanation in the link. SM

[lemur]

Lemur. This quote- "In reality, ad hominem is unrelated to sarcasm or personal abuse. Argumentum ad hominem is the logical fallacy of attempting to undermine a speaker's argument by attacking the speaker instead of addressing the argument" can be found here- http://plover.net/~b.../adhominem.html

 

You can only communicate if you know the language. I suggest that you read the explanation in the link. SM

You're strawmanning me as saying that the ad hominem attack related to the sarcastic approach to expressing it. The post compared me negatively with Einstein instead of addressing the content of my post. That's ad hominem. It was basically said that I am too stupid or unqualified to even consider something I would say. The poster should have addressed the content of my post or not bothered. If they would have wanted to make a comment about Einstein's methods and techniques because it was relevant, fine. But it was just unconstructive to make a fuss over Einstein to reject the validity of my post as coming from me. If you consider my posts not worth reading because they come from me, why read and respond in the first place? I.e. why attack? Personal emotional issues?

Edited March 3, 2011 by lemur

[Widdekind]

This is not correct.

 

The stress energy tensor, like the curvature tensor to which it is equated by the Einstein field equations is invariant -- independent of the observer. Motion is not an invariant.

 

What about rotational motions, like the rotation of a star? Are you saying, that a (hypothetical) non-rotating star, would produce the same curvature, in spacetime, as a (realistic) rotating one ? If the SET 'looks like' velocities factor in, then how is it 'invariant' ? And, again, what about 'non-inertial' velocities, like rotations, which everybody would see the same, and which everybody would identify as different, from a static situation ?

 

There is also the concept of "invariant mass", which is the relativistic mass of a system of particles, measured in center-of-mass coordinates so that the total momentum is zero, so that the mass is [math] E/c^2[/math]. This corresponds to the mass that would be measured by a labratory balance for a macroscopic object -- a hot bucket of water in principle weighs more than a cold one.

 

What about motions being 'invariant' ? What makes 'thermodynamic motions' immune to the 'invariance' of the SET ?

[DrRocket]

What about rotational motions, like the rotation of a star? Are you saying, that a (hypothetical) non-rotating star, would produce the same curvature, in spacetime, as a (realistic) rotating one ? If the SET 'looks like' velocities factor in, then how is it 'invariant' ? And, again, what about 'non-inertial' velocities, like rotations, which everybody would see the same, and which everybody would identify as different, from a static situation ?

 

There is a rotational effect, the Lens-Thirring effect, aka "frame dragging" associated with a massive rotating body. I don't know much about it.

 

 

 

What about motions being 'invariant' ? What makes 'thermodynamic motions' immune to the 'invariance' of the SET ?

 

????????

[swansont]

You're strawmanning me as saying that the ad hominem attack related to the sarcastic approach to expressing it. The post compared me negatively with Einstein instead of addressing the content of my post. That's ad hominem. It was basically said that I am too stupid or unqualified to even consider something I would say. The poster should have addressed the content of my post or not bothered. If they would have wanted to make a comment about Einstein's methods and techniques because it was relevant, fine. But it was just unconstructive to make a fuss over Einstein to reject the validity of my post as coming from me. If you consider my posts not worth reading because they come from me, why read and respond in the first place? I.e. why attack? Personal emotional issues?

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Moderator Note

1. No, it's not an ad hom.

2. What you said was considered and rejected. Mentioning Einstein's method was relevant — the post was pointing out that it's the hard way.

3. The solution to anything you thinks is a rules violation is to report the thread.

 

What the solution is NOT, is to derail the thread by complaining about the incident. The solution is also NOT to ignore staff. Nor is the the solution to then go and actually violate the rules by flaming and making an actual personal attack.

 

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Moderator Note

Relativistic mass discussion split off http://www.scienceforums.net/topic/55378-relativistic-mass/