Gravity and The Curvature of Space Question

[CraigS]

Originally Posted by sjastro

The question as to why mass bends space-time is totally meaningless if
you notice that (3) and (4) are the same statements. This is the equivalence principle of GR at work.

Hi Steven;

Great to have you 'back on the job' !

This is interesting for me.

I get that the question is not relevant in GR, however, when one attempts to ponder gravity from a quantum perspective, gravitons seem to appear. I think most would also be aware that attempting to incorporate gravity into the quantum world, then results in all of those famous problems which ultimately results in Grand Unification Theories (GUTs).

I find it fascinating that the various theories beyond GR, have been framed around attempting to address these problems in such a way as to explain everything from the quantum level up to, and including the bigger things more influenced by gravity. Field theories seem to also fall into a similar category. (I'm not quite not sure about this, yet).

I wonder about the influences this approach might have in shaping the initial foundations of the GUTs. It seems that there may well be artefacts lurking in these theories, originating from their initial premises.

I guess this is more a philosophical issue about the science theory creation process, as opposed to a technical one.

Interesting.

Cheers

[mjc (Mark)]

Steven

Thanks for your reply - I think you've given me the nudge or clue that I was seeking. By viewing the problem in space-time I can see that at the event horizon the past light-cone of an observer would be outside the event horizon while the future light cone will lie within and the light-like edge boundary of the light cones will lie on the event horizon.

Your post led me onto this page - and both have helped considerably.

http://www.phy.syr.edu/courses/modul...arzschild.html

I can't say that I immediately understand the tipping inwards of the light cone - but at least I have some handle to the answer.

Regards

Mark C.

[sjastro]

Originally Posted by mjc

Steven

Thanks for your reply - I think you've given me the nudge or clue that I was seeking. By viewing the problem in space-time I can see that at the event horizon the past light-cone of an observer would be outside the event horizon while the future light cone will lie within and the light-like edge boundary of the light cones will lie on the event horizon.

Your post led me onto this page - and both have helped considerably.

http://www.phy.syr.edu/courses/modul...arzschild.html

I can't say that I immediately understand the tipping inwards of the light cone - but at least I have some handle to the answer.

Regards

Mark C.

Mark,

In flat space the future light cone (and also the past light cone) forms a 45 degree angle with the time and spatial axes. This means the photon can move both in time and space from an observer's frame of reference.
The 45 degree angle tells us why photons travel in null geodesics and that the speed of light is the same for all inertial observers.

The situation becomes somewhat more complicated in gravitational fields. The closer a photon is to the event horizon the greater the gravitational redshift of the photon. The amount of tipping of the light cone is related to the gravitational redshift. A photon at the event horizon appears to be "stationary" to all observer's outside the event horizon. Each observer is still able to measure the passage of time but the photons do not appear to move spatially. An outgoing light cone edge that is vertical or parallel to the time axis means that the photon is spatially restricted to a particular value which in this case is the radius of the event horizon.
Inside the event horizon the light cone will never intercept the outside observer's world line hence it will never be seen.

Regards

Steven

[xelasnave]

Sorry I had to go out home where there is no electricity etc to check my carbon sinks
Thank you again Rohb, Craig and Steven for you help in attempting to understand the concept of space time.
Craig is correct about my interest in "the Theory of Everything" or the unification of all the forces and it is that interest that perhaps leaves me hunting for a messenger particle to make gravity work.
I recall Prof Hawking commenting that he received about three TOE,s per day at one stage so one could assume there are others interested the unification of the forces.
I understand what Rohb is driving at and such an approach is reasonable and yet I still believe that the operation of particles must at some level be able to explain the behavior of space time. Standing back and trying to follow the approaches of those interested in quantum mechanics and then those interested in general relativity it seems there is a difficulty in the two sides being reconciled. I dont think there needs to be any gap between the two in so far as I imagine that particles must causes the things we call properties of space time.... and I know this is probably offensive to both camps but remains my view.

I am starting to think that all fields must be a movement of particles that produce the field as opposed to a field causing the movement of particles... can I prove this ... no of course not ... I simply like the idea.
AND preference is not what guides science so it stands where it does as a mere idea.

Thanks again for starting a great thread Mark
alex

[mjc (Mark)]

Thanks Steven

I think I'm getting it. I'm glad I made the original post. Got to mull it over for it to settle but I do think I'm getting it.

Mark C.

[CraigS]

Alex;
Interesting. I find it fascinating that you keep gravitating () back to a particles only view of it all, when there are so many other ways of looking at it.

At the moment, the particle view results in problems when considering the 'big picture', which is why mainstream scientists have developed the other concepts.

Why don't you follow that same path ? (I'm interested in why you are reluctant to move out of the hole made plainly visible by quantum mechanics' present boundaries. I mean, its your choice … so why not take the plunge ?).

Cheers

[xelasnave]

Originally Posted by CraigS

Alex;
Interesting. I find it fascinating that you keep gravitating () back to a particles only view of it all, when there are so many other ways of looking at it.

At the moment, the particle view results in problems when considering the 'big picture', which is why mainstream scientists have developed the other concepts.

Why don't you follow that same path ? (I'm interested in why you are reluctant to move out of the hole made plainly visible by quantum mechanics' present boundaries. I mean, its your choice … so why not take the plunge ?).

Cheers

Craig a simple answer can be found in my ignorance of things in general.

I have done my best to understand General Relativity but it is not all that easy for me. At this point it seems to me to be complex geometry at work to describe something we dont understand but nevertheless works well ..so well in fact many think there is little need to ask any more of GR than what it has given us already.

I guess I like a particle approach because we deal with a physical unit.
Also something I have not said before is I find the concept of energy difficult and have to see it as an operation of very very small particles...even momentum I see a particle explanation
No doubt you "see" a wave as being able to operate in the absence of a particle background whereas I can not imagine a wave other than some form of particle movement say like an actual wave in water... I know in physics it is not seen that way.

Anyways as difficult as it is for me I hang on trying to learn more about the accepted physics and the kind folk here are always most helpful and extremely tolerant of my ignorance of much stuff. Its not a case of not coming around but more of I dont understand something others find in GR that I dont see.... but I continue to try rather than like many others simply throw it out trying to put in its place a different idea.
I never see the push gravity thing as interfering with GR as strange as that may seem..I think it is the particle flow I envisage that "bends" the geometric grid of space time ... but dont place too much on any of this as they are just ideas. AND given some of the seemingly wild ideas presented at the cutting edge of theoretical physics I dont feel my stuff is wild at all....but with no math one is branded as an idiot for radical views... I cant help that nor worry about folk who will be so critical at my attempts at original thought. To gain knowledge I dont care about what folk may think really.

I feel the key to understanding everything finally will probably come from ideas from both camps and maybe even ideas from the EU approach.
AND as to difficulties with a quantum approach I think it simply means there is more work to do to make it all work.

I would like to think I am at least responsive to the knowledge folk here provide and if nothing else very grateful for same.
alex

[mjc (Mark)]

Alex

I think we all try to justify things in terms of stuff that we are comfortable with.

I do it.

But I think it is important to try - and one can try and fail - to understand the other guy's perspective. I've learned stuff - in more than one walk of life - of how things work on the basis of constant re-engagement of something that should be beyond me and ended up in a better than expected understanding for someone without any grounding in the first place. It's like a child learning a language - with enough engagement a certain understanding is attained.

I don't pretend to be as competent as those I've learned from but I learn something with each engagement.

Mark C.

[xelasnave]

Yes indeed Mark.
It probably does not come across this way but I try to look at everything and understand what others see in it... It is clear I have doubts about stuff but I hang in because that is the only way to move forward. If one closes ones mind to settle upon one view I feel that is not helpful. The greatest minds on the planet wrestle with the sort of stuff we chat about here and we are very lucky to even get a look in...
I find this forum invaluable.

alex

[mws (Michael)]

My understanding of matter approaching the event horizon of a black hole is that will never actually enter the black hole, because of the extreme gravitational fields present, time will be slowed to such an extent that it would take an eternity to cross the horizon.

Michael

[CraigS]

Originally Posted by mws

My understanding of matter approaching the event horizon of a black hole is that will never actually enter the black hole, because of the extreme gravitational fields present, time will be slowed to such an extent that it would take an eternity to cross the horizon.

Michael

Hi Michael;

Nice to meet you.

If matter falls towards a black hole, (due to the gravitational attraction forces caused by the density of matter inherent to a black hole), it will pass through the Event Horizon, (unnoticed by the falling matter), speed up to close to the speed of light, heat up, become 'spaghettified', (if the hole is a small one), and eventually decompose. Its remnants will become part of the black hole matter.

An observer watching the matter fall however, would, most likely, see the matter slow to a standstill, heat up and decompose into its fundamental constituents. The sub-atomic picture of the decomposition into its fundamental components changes, depending on the model's assumptions of sub-atomic physics.

Cheers & Rgds.