Galaxies going faster than light ? [v.2]

Australia it seems is cut off from discovery science channel.

To bad . It leaves you behind .

 

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Good question! And sorry I missed it earlier.
From a distant point far way, spacetime is expanding and the galaxy/group is being taken along for the ride. We see that evident as a cosmological red shift.
From a point within that group, eg: similar to say someone in Andromeda, viewing the Milky Way, [both within our local group] then no expansion from within that is evident....they are gravitationally bound and decoupled from any overall large scale expansion.
But certainly, someone within that distant group, also views our own local group of galaxies as moving away at "c" or FTL, due to the large scale spacetime expansion, just as we view them.

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Firstly the center of the Universe is a invalidated concept.....there is no center [see the Frazer Cain video.....
If I understand you properly, anyone within that group, the same as anyone withing our local group, do not see any expansion within that group due to gravity overcoming any local spacetime expansion.
But as I just said, they would view us, and we would view them, as moving away at FTL, due to spacetime expansion.

And I have no qualms admitting sometimes my own explanations maybe confusing, so perhaps Dave may like to contribute again and explain further?

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Aye, because in essence, they are not moving through space at "c", but rather moving with space at its already impressive expansion rate, +/- whatever speed the galaxy is actually moving through space... cool stuff!

Yeah, poor choice of words on my part lol... but I think you got the point regardless. It's insane how much perspective can influence things XD

The mark of true science is to first admit when something is unknown

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True

And which NASA DID surprisingly .

 

Better yet. Don't get your science education from pop TV shows.

 

The Interesting point re travelling at "c" is that from the photon's frame of reference [which I admit is hard to imagine] time comes to a stop, and length contraction is infinite, which literally means that a photon experiences no time and no distance: It can traverse the whole Universe in an instant!
Mind boggling stuff, but just confirming another postulate of SR re frames of references and how each and all is as valid as each other.
So while we see light from the Centauri system take 4.3 years to reach us, if you were a photon, you see that 4.3 years as an instant!

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Makes sense in a way, given time dilation and such. From its point of view, time hasn't passed much, if at all. It is an interesting thing that we will have to contend with as we (or perhaps, if we) ever start building craft capable of velocities approaching mid to high fractions of c... cause it would REALLY suck for someone to experience a four month journey out, four months there, four months back, and find that an entire generation of their family has been born, grew up, grew old, and died lol...

 

Not quite.

A photon does not have a valid frame of reference at all.

1. Light, by the postulate of SR, always moves at c in all reference frames.
2. By definition, an object is at rest in its own reference frame.

The result - if photons were asserted to have any kind of reference frame at all - is that you would have an object that is both stationary and moving at the speed of light simultaneously.

This is an explicit contradiction. It cannot happen.

 

Read
- Joe Haldeman's Hugo/Award-winning novel The Forever War,
- Larry Niven's Locus/Ditmar-nominated novel A World Out of Time,
- John Varley's Hugo/Locus-winning, Nebula-nominated short story The Pusher.

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Yep, OK, thanks Dave, well put! Actually used the wrong word where I put in brackets, " which I admit is hard to imagine" More approriate would have been the FoR of a photon is meaningless.
Thanks again.

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Seeya in around 12 days!

 

Question then - the experiments in which they have "frozen" photons of light via laser interactions and a medium (http://io9.gizmodo.com/scientists-freeze-light-for-an-entire-minute-912634479 as an example) - would the "stationary" photons have a frame of reference at that point?

As for those books, I'll have to see if I can loan them out from one of the libraries near me (doubtful), or wait until I can purchase them myself

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Assuming that they exist, they would seem to be moving faster than the speed of light, relative to us.

No, I didn't see the program. I assume that it was referring to this:

http://phys.org/news/2015-10-galaxies-faster.html

http://curious.astro.cornell.edu/th...rom-each-other-faster-than-light-intermediate

The "explanation" for this idea is that while relativity forbids motion through space at velocities faster than the speed of light, it doesn't forbid space from expanding at a faster rate.

The Hubble constant provides a ratio of expansion (red shifts) to distance, and extrapolating it out implies that at a distance of 13.8 billion light years (isn't that roughly the age of the universe since the 'big-bang'?), the universe would be expanding at faster than the speed of light. So any galaxy more distant than that will (arguably) be receeding relative to us at more than the speed of light.

Could we observe such a galaxy? Seemingly the answer is 'yes' if the light we are observing left the galaxy early in the universe's history. But light that leaves these superluminal galaxies now will never make it to us since the distance between here and there is growing faster than the light is moving. So over time, galaxies disappear over the cosmic horizon, so to speak.

They say that late in the heat-death of the universe, most of the universe we presently see in the sky today will recede over that horizon as the universe continues to expand. So the sky will become empty and dark.

As a layman, I remain a bit skeptical and unconvinced by most of this kind of stuff. It's all based on huge extrapolations of theories that may or may not be as sound as people currently believe they are.

 

That's one of the things that annoys me about physics. It tells laymen like me that the speed of light is a constant in all frames and that nothing with mass can exceed the speed of light... except when they tell us that isn't true.

When intelligent laypeople point that out, there's often condescension in the reply. At the very least, it makes science stop being fun.

 

The dual nature of light states that it is both particle and wave.
They're not stopping photons; they're stopping the propogation of the EM waves.
The photons travel through a medium by way of absorption and re-emission from atoms. They can trap the re-emission. Thus, the light does not progress, but at no time are there photons travelling at any other speed than c.

 

This isn't limited to physics, or even science. All specialties require in-depth understanding (plumbing, electrical, watercolour, ballet) beyond the layperson.

Too often people think that what they learned in high school is the whole picture. Learning a specialty is hard work. (Otherwise, everyone would be an expert at everything.

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)

The idea of simplistic, primer explanation has a technical term, although it sounds derogatory: Lies to Children.

"...a simplified explanation of technical or complex subjects as a teaching method for children and laypeople..."


Alas, even when there is no condescension, there is an unavoidable shift from peer-peer to teacher-student.

 

If I'm understanding what you said correctly... wouldn't that mean the photon never actually moves, but simply is absorbed and re-emitted over and over? Wouldn't that preclude travel through "empty" space?

Actually, that is something I've not quite gotten my head around as well... is "empty" space truly empty... eg, if we were to take a "sample" of space, say one cubic foot, that was devoid of any matter... would it actually be "empty", or at infinitely tiny scales, would it still be occupied (be it by quantum foam or what have you)?

 

the thing that is missing in all of this discussion ; is that NASA its self has discovered that either galaxies or something else is , is in fact travelling faster than the speed of light .

and the fact that NASA is admitting this ; since this institution tends to be more mainstream in its thinking than , outside the box thinking , should be taken more seriously than most posters have been.

NASA people are telling us something .

 

No, again, the galaxies aren't moving through space faster than light, the space inbetween them is expanding.

 

so you think that NASA has not thought about this ? why ?

 

I think it's quite the opposite - they have. The issue is that, in translating their findings to layman's terms, important information is lost - just look at my own misunderstanding of the meaning for "frame of reference" as a good example of that. To the logic I was using, what I said and inferred from their findings made sense (that from our position, a galaxy may appear to be moving ftl, when in fact it is moving sunlight but the space between it and us is also expanding, resting in a net appearance of ftl travel)

unfortunately, the logic itself was flawed due to my misunderstanding of some of the terminology - it doesn't mean that my reasoning was flawed (based on my available knowledge, the logic was sound) , but the conclusion was still inaccurate because of the lack of understanding on my part.

I don't know if I'm explaining that we'll at all... lol