Can space bend faster than light?

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Can space bend faster than light?

Postby tj444 on December 20th, 2016, 6:10 pm 

I put this in beginner because I need an easy to understand answer and don't know much.

Space can expand so isn't expanding bending?

Also I want to make sure someone doesn't interpret this to mean that bending = expanding. For all I know bending = expanding could be the same thing or completely different. Is it it the same? I guess bending needs mass. Does expansion of the universe need mass? I always thought the answer is yes. Don't really know why. Can someone explain this to me.

But even when space expands and bends the fastest something can move is a gravitational wave. Gravitational waves travel at the speed of light. Just stating something I understand.

Maybe the faster than light expansion is the cause of quantum mechanics. Is that possible?

Also I have another question. If space can bend faster than light could that explain the quantum nature of the universe? Example quantum entanglement etc. Or am I mistaken.

I do understand a tiny bit about Einstein theory but not very much and none of the math. I understand bending of space. Light is fastest something can travel and make a accurate prediction. That is about all I understand about relativity. Take that into consideration when answering the question.
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Re: Stretching past limits.

Postby Faradave on December 21st, 2016, 1:25 am 

If you pluck one end of a long rubber band, the signal will propagate along it toward the other end at a certain finite speed (not greater than the speed of sound in that material).

Imagine a very long rubber band, with one end fixed and the other end is attached to rockets that stretch the band much longer. If you pluck the band at its fixed end, it's conceivable that the band expands faster than the propagation rate of the signal. Under such conditions the signal would never make it to the other end.

Our universe is very large and appears to be expanding at a rate proportional to how far any two distant locations are separated. It is expected that some locations are so far away from us that they are "receding" faster than universal speed limit c. Nothing, including light or perturbations of spacetime (gravitational waves) would be expected to communicate between such locations. Such separations about a given location make up its "cosmic event horizon".
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Re: Can space bend faster than light?

Postby Dave_Oblad on December 21st, 2016, 3:37 am 

Hi Faradave.

Even if the Horizon is heading away from us at 2c, we can catch it at 1/2c because the closer we get to it, the slower it recedes relative to us. Light from stars on the opposite side of the Universe will eventually reach us, unless you want light to stop at 0c somewhere along its journey to us.

At least that was a point someone (Marshall?) made here a few years ago uncontested. Not sure if I agree.

Regards,
Dave :^)
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Re: Can space bend faster than light?

Postby BadgerJelly on December 21st, 2016, 5:05 am 

Scientists are forced to use analogy and metaphor to describe their art. "Expansion" and "bending" are the concepts we have that apparently best help us frame the meaning of the scientific data in a comprehendible and logical fashion.

It may help if you attempt to employ other senses to investigate the concepts? I curious as to how a congenially blind physicists come to terms with "expansion" and whether their view is more in tune with what the data says?

I guess to the congenially blind "light" is merely a form of heat they cannot sense. If you then think about light as "heat" it may be easier to think about entropy too?
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Re: Recession rate vs. Speed

Postby Faradave on December 21st, 2016, 10:15 pm 

We start with the understanding that gravity locally overwhelms expansion. So expansion is observable at scales incorporating lots of empty space.

Then we must recall that an expansion rate, though measured in the same units as speed is still quite different than speed. Speed is motion relative to space. Something with speed changes location in space. As such it is observable quite readily in the locality of gravitation. Expansion is the separation of locations, which are themselves at rest.

So, on a stretching (i.e. expanding) rubber band, anchored at one end (for reference only), an ant may run away from the anchored end at a certain speed (say 2 cm/s) relative to the rubber. If the far end of the band recedes at more than that rate, the ant will never reach it. Note that with expansion, nothing is moving relative to the rubber, however locations along the band still recede from each other in proportion to their separation.

Dave_Oblad wrote:Even if the Horizon is heading away from us at 2c, we can catch it at 1/2c because the closer we get to it, the slower it recedes relative to us.


The point is that at 0.5c, we never get closer to a location receding at greater than 0.5c. It is true however, that observers closer to our event horizon than we are may well be able to cross it.

Light emitted toward us, from beyond our event horizon, will never reach us because we are beyond the emitter's event horizon (thus, moving away from it faster than c.)
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Re: Can space bend faster than light?

Postby Dave_Oblad on December 22nd, 2016, 6:14 am 

Hi Faradave,

I would agree if the expansion is due solely to addition of new Space. But if some part of that is stretching Space, then the ant will be taking longer steps along his path. If expansion is only stretching then no problem, the ant will easily reach the other end. Remember.. the ant stretches with space too.

The final view is how much of Expansion is due to Stretching vs Addition. The nagging question in my mind is that light from far away has been stretching for a long time. When it suddenly re-enters compressed Space (Ie. Gravity Well) will it fully reconstitute to its original wave length?

I think Faradave gets this, as his Model is like mine regarding Radial Time.

Regards,
Dave :^)
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