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Stretching the Fabric of Space-Time


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Since the universe is expanding, does that mean that the fabric of space-time is stretching or that more fabric is being made? Or am I just totally out of the ballpark?

 

What fabric?

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The best interpretation, in my non-expert opinion, is given with the help of cosmology's standard model and its FLRW metric. Space is expanding over time. Expanding exponentially faster and faster most likely too.

Edited by Iggy
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In the expansion of space, the distance between galaxy clusters is increasing. Does this mean there is more space between the clusters as time goes on? Yes. Thinking of space as a fabric is just an analogy, not to be taken literally.

 

I believe the NASA figure above is meant to show how the spinning of the Earth drags space around with it -- a phenomenon called frame dragging. In the Gravity Probe B satellite, a set of gyroscopes were set to point in a certain direction. Over time, they drifted ever so slightly. The average amount of drift agreed with frame dragging predictions (to about 20%, I think). Objects in "empty" space (gyros) were affected by the spinning of a distant object (the Earth). Another strange prediction of general relativity confirmed.

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I don't understand the image. It is the first result from a google image search for "spacetime" or "the fabric of spacetime". Wikipedia's spacetime article has almost the exact image at the top of the article.

 

But...

 

It looks to me like a plot of gravitational potential -- what comes to my mind when I think of a gravity well. The fabric of spacetime around the earth (ie 'the spacetime continuum' or just 'spacetime') would evoke in me something closer to this: curved spacetime simulation

 

Unfortunately, almost all of the image results from searching "spacetime" are what look to me like gravitational potential so maybe I'm missing something.

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It is not a plot of the gravitational potential, note where the lowest point is, 'below' ( or is that above ?? ) the earth.

It is also not a representation of frame dragging as the plot would then be twisted counter clockwise due to the earth's rotation.

 

It is a two dimensional representation of the three dimensional space foliation of space-time. In this representation ( 2d space plus time ) the time dimension would be more foliations stacked on top of the one shown, representing future instants, along with more foliations below the one shown, representing past instants. Anyone with even a little understanding of GR will know that this representation is not exactly accurate, but suffices for simple explanation.

It is analogous to the 'bowling ball on the rubber sheet' diagram which is used to illustrate black holes.

 

For obvious resons, the 3d space plus time representation would be impossible to draw.

Edited by MigL
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This fabric

162571main_GPB_circling_earth3_516.jpg

Credit: Nasa

 

No spacetime fabric here, only an artistic [*] representation of spacetime curvature.

 

[*] "artistic" because that is not what general relativity says. This artistic representation is sometimes named the "rubber-sheet analogy".

Edited by juanrga
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It is not a plot of the gravitational potential, note where the lowest point is, 'below' ( or is that above ?? ) the earth.

I don't see the significance of how the two are superimposed in the vertical. AS a 2D plot of potential it wouldn't matter -- it wouldn't have physical meaning -- where it's attached in earth's 3rd dimension.

 

 

It is a two dimensional representation of the three dimensional space foliation of space-time. In this representation ( 2d space plus time ) the time dimension would be more foliations stacked on top of the one shown, representing future instants, along with more foliations below the one shown, representing past instants...

That would make it two curved spatial dimensions. No depiction of time.

 

I think the rubber sheet / bowling ball analogy does a lot more harm than good. As an analogy for a gravity well... or more specifically for gravitational potential... ok, but it doesn't really communicate the fabric of spacetime.

 

//edited wording

Edited by Iggy
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Question.When they accelerate particles at the LHC,by inputting a lot of energy and then focusing that energy at the point of collision,are they causing new particles to emerge from the fabric of space?Does the idea of a Higgs boson imply that there is a fabric of space?

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