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only1universe
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Basically since we use QM for the very small, and GR for anything bigger than an Atom, can we assume GR has no place in the universe if there is no matter?
Bill_K said:Gravity couples to energy, not to "matter". Does your universe without matter also have no electromagnetism?
Bill_K said:Gravity couples to energy, not to "matter". Does your universe without matter also have no electromagnetism?
Galron said:GR always holds it is a law. If it doesn't hold then you would ask the question why not. I know that sounds Zen but think about it...
Ok now you have reached Nirvana. In what universe would GR not apply?
only1universe said:a universe where none of what it governs exists :)
Galron said:
utesfan100 said:It seems to me that in an empty universe GR would still apply, and result in a Minkowski metric.
But then, what is a metric without an observer? Unless we have a mass-energy free observer somewhere ... hovering over the face of a bland and lifeless void.
only1universe said:Could a vacuum act as an observer? It seems the fact that it can and does interact with particles and/or vacuum pressure fluctuation would be re-iterating information.
Drakkith said:That depends on what you mean by vacuum. In reality a vacuum is still occupied by various fields, as the electromagnetic force and gravitation have an infinite range. We usually mean vacuum to be the removal of nearly all matter within a volume. If you mean vacuum to be the absence of absolutely everything, all matter, energy, and mass, then I don't see how, as not only would there be nothing to observe, but I'm not sure you could even call this vacuum "something".
only1universe said:Whats the minimum that would be required for there to be a negative vacuum pressure? Could there be a negative pressure simply due to the absence of matter once all else is removed?
Drakkith said:Matter or mass?
only1universe said:Mass gone, matter's ability to take up 3 dimensions leaves a negative vacuum pressure in its absence.
Drakkith said:It is the mass that affects spacetime, not the matter itself. The ability for matter to form 3d structures has nothing to do with vacuum pressure. As to the absence of mass, I don't know. If having no mass affected the vacuum pressure, then I would expect the existence of mass in an area to slow down local expansion. However I have no idea if this is true or if it measureable on such short scales.
only1universe said:Well if having no mass did effect the pressure, I'd have to say that masses information had been observed by the negative vacuum pressure. Which leads me of course to wonder if negative vacuum pressure can induce energy and mass again.
GR stands for General Relativity, which is a theory of gravity proposed by Albert Einstein. It describes how massive objects in the universe interact with each other through the curvature of space and time.
Matter plays a crucial role in GR as it is the source of gravity. According to the theory, the presence of matter causes the curvature of space and time, which in turn affects the motion of other objects.
No, GR cannot exist in a universe without matter. As mentioned before, matter is the source of gravity, and without it, there would be no curvature of space and time, making GR irrelevant.
Yes, in addition to matter, energy and momentum also have an impact on the curvature of space and time in the theory of GR. This is known as the stress-energy tensor and is an essential component of the equations of GR.
If GR did not exist, our understanding of gravity would be drastically different. The universe may look very different, as the behavior of massive objects would not be governed by the curvature of space and time. It is difficult to predict precisely what would happen, but it is safe to say that the universe would not be the same as we know it.