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Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

What happens to the fabric of space-time when an object moves through it near the speed of light?

First of all, space-time is not a fabric. Space and time are not tangible 'things' in the same way that water and air are. It is incorrect to think of them as a 'medium' at all. No physicist or astronomer versed in these issues considers space-time to be a truly physical medium, however, that is the way in which our minds prefer to conceptualize this concept, and has done so since the 19th century. Back then physicists talked of an ether. Today we know that ethers of the kind that behave like a physical medium are simply not present.

We really do not know what space-time is, other than two clues afforded by quantum mechanics and general relativity. General relativity as developed by Albert Einstein, says, and this is a direct quote from Einstein, that

"Space-time does not claim existence in its own right, but only as a structural quality of the [gravitational] field".

Added to that are comments by theoreticians such as Nobel lauriat Steven Weinberg

"Space and time coordinates are just four out of many degrees of freedom we need, to specify a self-consistent theory. What we are going to have [in any future Theory of Everything] is not so much a new view of space and time, but a de-emphasis of space and time",

A similar view is expressed by a co-inventor of super-string theory, Michael Greene:

"In the theory of gravity, you can't really separate the structure of space and time from the particles which are associated with the force of gravity [ such as gravitons]. The notion of a string is inseparable from the space and time in which it moves.".

These are quotes out of Paul Davis's book "Superstrings: A Theory of Everything?"

Finally, as Einstein noted "Space and time are modes in which we think, not conditions in which we exist" which is a view also expressed in 900 AD by the Arabic physicist Ikhwan al-Sufa, "Space is a form abstracted from matter and exists only in consciousness".

So, the question about what happens to space-time when a particle moves through it at near the speed of light is answered by saying that this is the wrong question to ask. Just because the brain can construct a question doesn't mean that the question has a physical answer!

Return to the Special & General Relativity Questions and Answers page.

All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.