[evan_au]

Recent attempts to measure the rate of expansion (the Hubble "constant") appear to give slightly different results.
http://www.scientificamerican.com/article/cosmic-speed-measurement-suggests-dark-energy-mystery/

[McQueen]

The most fascinating aspect of this subject  is that the Universe is actually expanding faster than the speed of light. Impossible right ? That is what the astronomers who first made the discovery thought. For this reason for a long time this evidence was ignored. However, the rate of expansion at 13.6 billion years was measure at five times the speed of light ! Think about it, it shouldn't happen. Yet under the special conditions prevailing in the early Universe it might have been possible. This is exactly my point, if the Universe was expanding at FTL speeds, it can no longer be doing so, because in our own local space FTL speeds are just not possible and we have physical evidence to this effect. Therefore what we are seeing is evidence form 13.6 billion years ago , when the Universe was young and the acceleration due to the inflationary process was still very apparent.

[PmbPhy]

Clearly contradictory dogma, ...

Not only a rude response but an ignorant one as well. I refuse to respond to each of those totally rude and ignorant responses. You don't have the knowledge nor intelligence to properly understand the answer.

If you actually chose to study physics in my forum like you agreed to rather than squander that opportunity then you might one day have learned what it means for space to expand. That has a precise meaning which you've never taken the time to learn. That space itself can be altered has been demonstrated to be true in experiments. But you're too ignorant to understand its meaning and you'll remain so until you make the effort to learn. However that requires having an open mind which is something you don't have.

Note: Chances are that you'll mistake my use of the term "ignorant" to mean "stupid". That is not what it means. The term ignorant is defined as lacking knowledge or information. However your constant ignorant responses and rude attacks do demonstrate to me a person of lesser intelligence than normally displayed by the members of this forum. Most people here are rather intelligent and wouldn't post such rude comments. Most of them would ask what physicists mean whey the speak of space expanding or changing.

[PmbPhy]

The most fascinating aspect of this subject  is that the Universe is actually expanding faster than the speed of light. Impossible right ?

Not at all. It doesn't even violate special relativity which implies that nothing can travel faster than light since its speaking only of objects traveling in space. It doesn't have anything to do with how fast space itself is expanding or how fast two objects which are at rest in an expanding space can move apart.

That is what the astronomers who first made the discovery thought. For this reason for a long time this evidence was ignored.

That's news to me. Where did you get such an idea from? General Relativity (GR) has been around since before that discovery was made and its GR that can explain it.

However, the rate of expansion at 13.6 billion years was measure at five times the speed of light !

Where did you get such a figure from? It makes no sense to speak of space expanding at a particular speed since the speed at which two objects recede from each other depends on the distance between them.

Think about it, it shouldn't happen.

I disagree and so do all the cosmologists in the world who understand general relativity.

  This is exactly my point, if the Universe was expanding at FTL speeds, it can no longer be doing so, because in our own local space FTL speeds are just not possible and we have physical evidence to this effect.

You're confusing the speed of an object moving in space with the speed of an object due to the expansion of space.

Therefore what we are seeing is evidence form 13.6 billion years ago , when the Universe was young and the acceleration due to the inflationary process was still very apparent.

And yet space is still expanding and objects are still moving FTL because of it.

[McQueen]

Not at all. It doesn't even violate special relativity which implies that nothing can travel faster than light since its speaking only of objects traveling in space. It doesn't have anything to do with how fast space itself is expanding or how fast two objects which are at rest in an expanding space can move apart.

Maybe this is too nonchalant a dismissal of what after all is an unusual event.  In fact while doing a ( admittedly cursory search of the forum) I couldn't find a single reference to faster than light expansion of the Universe ! In fact the only reference to this subject appears to be from threads that I have posted.  That having been said the implications remain, so space expanding doesn't come under special relativity ?  When you use the term fast you are implying objects moving with velocity so how actually doesn't this count. ?

That's news to me. Where did you get such an idea from? General Relativity (GR) has been around since before that discovery was made and its GR that can explain it.

Once again I see the same dogged pedagogy, where only one explanation exists and nothing else can be right. For your information there are several reasons put forward for faster than light expansion of the Universe and the theory I have outlined here happens to be one oof the major ones:
Perhaps it's dark energy acceleration, or the earliest inflationary period of the universe when EVERYTHING expanded faster than the speed of light.   Read more at:

I disagree and so do all the cosmologists in the world who understand general relativity.

See answer above.

I disagree and so do all the cosmologists in the world who understand general relativity.

Again just one viewpoint and a highly disputable one at that

[stacyjones]

Our visible Universe is a larger version of what is represented by the blue lines in the following.



'Supermassive Black Holes Transport Matter into Cosmic Voids, Astronomers Say'
sci-news.com/astronomy/supermassive-black-holes-matter-cosmic-voids-03658.html

“Some of the matter falling towards the holes is converted into energy. This energy is delivered to the surrounding gas, and leads to large outflows of matter, which stretch for hundreds of thousands of light years from the black holes, reaching far beyond the extent of their host galaxies,” the astronomers explained.

At the scale of our Universe the energy referred to above is dark energy. A Universal black hole is powering our visible Universe causing the galaxy clusters to accelerate away from us.

[guest39538]

At the scale of our Universe the energy referred to above is dark energy. A Universal black hole is powering our visible Universe causing the galaxy clusters to accelerate away from us.

That is interesting, how would that compare to a stationary universe that gained motion because at a relative central point a single planet changed in entropy causing the universe to inflate away from this point?

[stacyjones]

At the scale of our Universe the energy referred to above is dark energy. A Universal black hole is powering our visible Universe causing the galaxy clusters to accelerate away from us.

That is interesting, how would that compare to a stationary universe that gained motion because at a relative central point a single planet changed in entropy causing the universe to inflate away from this point?

A Universal black hole powering our visible Universe explains why most everything appears to be accelerating away from us. The stuff that has been getting pushed for longer than we have is accelerating away from us. We are accelerating away from the newer stuff that has been getting pushed for less time than we have been. From our perspective, most of the matter is accelerating away from us.

A Universal black hole powering our visible Universe also explains the directionality of the matter associated with the dark flow (https://en.wikipedia.org/wiki/Dark_flow). The energy associated with the Universal black hole is pushing the matter associated with the dark flow, causing it to move directionally through our visible Universe.

[guest39538]

At the scale of our Universe the energy referred to above is dark energy. A Universal black hole is powering our visible Universe causing the galaxy clusters to accelerate away from us.

That is interesting, how would that compare to a stationary universe that gained motion because at a relative central point a single planet changed in entropy causing the universe to inflate away from this point?

A Universal black hole powering our visible Universe explains why most everything appears to be accelerating away from us. The stuff that has been getting pushed for longer than we have is accelerating away from us. We are accelerating away from the newer stuff that has been getting pushed for less time than we have been. From our perspective, most of the matter is accelerating away from us.

A Universal black hole powering our visible Universe also explains the directionality of the matter associated with the dark flow (https://en.wikipedia.org/wiki/Dark_flow). The energy associated with the Universal black hole is pushing the matter associated with the dark flow, causing it to move directionally through our visible Universe.

Dark flow?  do you simply mean beyond the visible spectrum and Fr=0?


The same ''dark'' flow that makes this work

https://en.wikipedia.org/wiki/Crookes_radiometer


In the universe only exist two directions, - or + relative to the observer.   


Up down left right are not real, neither is north or south, in the universe our own evidence suggests that when things gain entropy they move + from a central point and vice versus when they lose entropy gain they - in direction and contract.

[stacyjones]

Dark flow? 

https://en.m.wikipedia.org/wiki/Dark_flow

[RobC]

You will probably realise from my posts that my knowledge of cosmology is rudimentary to say the least.

What I find fascinating is that the rate of expansion is accelerating.

Speculation for the cause?

[McQueen]

You will probably realise from my posts that my knowledge of cosmology is rudimentary to say the least.

What I find fascinating is that the rate of expansion is accelerating.

Speculation for the cause?

Firstly the Universe is everything, so there is nothing outside the Universe, If there was anything outside the Universe  it would also be part of the Universe.  So from our view-point the Universe is infinite.

Secondly a good analogy of the expanding Universe would be as follows:  Instead of an explosion, imagine the expanding Universe is like a loaf of raisin bread rising in the oven. From the perspective of any raisin, all the other raisins are moving away in all directions. This is all very well , the problem here is that it is possible to measure the rate at which the raisins are moving away from each other. So when speaking of either cosmological red-shift or a normal red-shift, the same principles of objects moving away from a location are involved. The fact that many of these cosmological red-shifts, seem to indicate near to light speeds or FTL  speeds is disturbing.  The only reasonable explanation would seem to be that when we see red-shifts that are close to C  or to FTL speeds, what we are seeing is the remnant of acceleration that took place at a time close to the Big Bang event. This is in fact one of the possibilities, that cosmologists agree exists.  So the Universe might not in fact be expanding and there is considerable proof that the Universe is instead slowing down.

To state that light can move faster than light because space itself is expanding allowing light to move FTL, even using GR sounds suspect, after all light within space and light within expanding space is still light or we wouldn't be able to record the red-shift in the first place.  How could we even record this light if space expansion gives it the ability to move at any FTL velocity ?

Here is a brief summary of why astrophysicists believe that FTL speeds are possible:

" Astrophysicist Edward Robert Harrison said, "Light leaves a galaxy, which is stationary in its local region of space, and is eventually received by observers who are stationary in their own local region of space. Between the galaxy and the observer, light travels through vast regions of expanding space. As a result, all wavelengths of the light are stretched by the expansion of space. It is as simple as that..."] Steven Weinberg clarified, "The increase of wavelength from emission to absorption of light does not depend on the rate of change of a(t) [here a(t) is the Robertson-Walker scale factor] at the times of emission or absorption, but on the increase of a(t) in the whole period from emission to absorption." "

As can be seen this theory seems to depend on some quite out f the way theories.

Between the galaxy and the observer, light travels through vast regions of expanding space. As a result, all wavelengths of the light are stretched by the expansion of space. It is as simple as that..."

The fact remains that light is travelling through vast regions of space, that would not result in red-shift, a red-shift would only occur IF an object were moving away, it has nothing to do with distance.

The increase of wavelength from emission to absorption of light does not depend on the rate of change of a(t) [here a(t) is the Robertson-Walker scale factor] at the times of emission or absorption, but on the increase of a(t) in the whole period from emission to absorption."

How  does time taken for absorption  produce red-shift effects ?

[savemars]

I keep hearing the Universe is expanding in comparison to like a balloon inflating, the evidence an apparent red shift observed of matter. We do not observe space red shifting we only observe light/matter interaction red shift, so how from that do you conclude the Universe is expanding when that makes no logical sense or is a any sort of rational thought?
I read this morning that it is now expanding faster than we first thought and soon and the Universe will become cold and the Universe will end, how on Earth doe's any one derive that ?

I believe I can explain it in a simple way. the universe is expanding (the distance between two objects) this can be shown with the classroom experiment showing gravity. if you have a sheet pulled then place a ball on it. this will create an example of a gravity well, but at the same time it will show the expansion of spacetime. while the ball pulls on the fabric it will cause the rest of the fabric to slightly expand. for every force there is an equal and opposite  force.

[evan_au]

The energy associated with the Universal black hole is pushing the matter associated with the dark flow, causing it to move directionally through our visible Universe.

From the link, Dark Flow is a trend of galaxies moving towards a certain patch of the sky
- Different physicists argue about whether Dark Flow is real or imagined, so it's not obvious that it exists
- If Dark Flowdoes exist, it is a small perturbation on the overall expansion of the universe
- So Dark Flow cannot explain the overall expansion of the universe, even if it is confirmed

[evan_au]

if you have a sheet pulled then place a ball on it. this will create an example of a gravity well, but at the same time it will show the expansion of spacetime. while the ball pulls on the fabric it will cause the rest of the fabric to slightly expand.

This analogy of spacetime is useful for showing the local distortion of spacetime caused by the presence of matter.
- That includes bending the path of light traveling near the Sun

However, if you wanted to show the expansion of the universe, you would need to then make the frame holding the sheet to expand, causing all objects on the sheet to move away from each other, at a speed proportional to their separation.

Like all analogies, you need to be careful of taking it too far. And sometimes it is better to focus one analogy on one effect (distortion of spacetime), and use a different analogy for a different effect (expansion of the universe).

I think some of the other analogies above are clearer for explaining the expansion of the universe:
- Blowing up a balloon: dots move away from each other
- Baking raisin bread (I liked that one... it works in 3 dimensions!)

[hamdani yusuf]

- Baking raisin bread (I liked that one... it works in 3 dimensions!)

It's also delicious, hence we can avoid leaving trash when the experiment is finished.
But still, it expands to space around it which was previously empty.

[Bill S]

But still, it expands to space around it which was previously empty.

Only if you accept that empty space really exists.

[hamdani yusuf]

But still, it expands to space around it which was previously empty.

Only if you accept that empty space really exists.

There was space which doesn't contain bread before the experiment, but does contain bread afterward.

[Bill S]

There was space which doesn't contain bread before the experiment, but does contain bread afterward.

True; but the space was not empty before the bread arrived.  What did the bread displace?

[Halc]

There was space which doesn't contain bread before the experiment, but does contain bread afterward.

True; but the space was not empty before the bread arrived.  What did the bread displace?

There is no known viable model of a bang happening at a location in otherwise empty space.  So the bread expanding into not-bread space analogy just doesn't work.  The bread is the space, and it having an edge would violate the cosmological principle on which all the theories rest.