The Universe expanding at the speed of light?

[Strattos]

Pardon me if this has been asked before. I am an avid follower of the latest scientific discoveries but by no means a professional scientist. If anyone could provide a link or explain an answer, I would greatly appreciate it.

 

If the Universe is expanding and speeding up, would it not be logical to assume that the expansion would eventually (if not already) reach the speed of light? Would we eventually arrive at that speed and what would the implications be?

 

Also, how do we know, from observation that the Universe isn’t slowing down? When we view the Hubble Ultra Deep Field it appears that Galaxies are moving exponentially faster away from everything. That observation is looking at things that are 13 billion years old. Is there evidence that proves the expansion is still occurring?

 

Thanks for your time!

[Spyman]

Here is a link to the Wikipedia article about the Big Bang theory, it has further links to expansion and other related science.

The mainstream though is that the Universe expanded very very rapidly already at the initial moment of the Big Bang. For instance the emitting locations of the Cosmic Microwave Background Radiation, that is the oldest remnant of the Big Bang that we can observe, was receding away from us with speeds greater than 56 times the speed of light when it emitted those photons that we recieve today.

The most distant object we have observed is a small and compact galaxy named UDFj-39546284, which has a preliminary redshift of 11.9 that indicates that it was receding away from us with around 4 times lightspeed 13 billion years ago when it emitted the light that reaches us now. Our standard model predict that the light we observe from it today was emitted from a distance of 2.5 billion lightyears and that the expansion has brought it away to a distance of more than 32 billion lightyears where it now recedes with slightly above 2 times lightspeed.

 

Gravity has fought against expansion and managed to cause its rate to slow down for billions of years, but roughly after half the age of the Universe the rate of the expansion started to speed up again. The sad implication is that the Universe will end very diluted, black and cold.

 

We are observing distant objects in the whole range from zero billion years to 13 billion years old and we have independent methods to find out both the light travel distance and the receding speed of the emitting object. With standard candles we can estimate how much space light has traversed to reach us and with cosmological redshift we can measure how fast the emitting object was receding from us at that time.

By comparing this data we can make models of the expansion and when we find that objects is much further out than expected with a slowing down expansion then we know that the expansion is not only still occuring but also accelerating. The 2011 Nobel prize was awarded for the 1998 years discovery from observations of distant supernovae that the expansion is accelerating since around 5 billion years ago.

Here is a great article from 1998 about the discovery in Science Magazine: Cosmic Motion Revealed

Edited December 13, 2012 by Spyman

[imatfaal]

Great answer by Spyman. Additionally on the accelerated expansion I would recommend the Nobel Lectures by Perlmutter, Schmidt and Riess. Not only do the lectures give a whistlestop tour of the observations and ideas that won them the Nobel prize; they are also very personal and let you glimpse the teamwork, camaraderie and rivalry that make a great group of scientists.

 

http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/#

[michel123456]

Here is a link to the Wikipedia article about the Big Bang theory, it has further links to expansion and other related science.

 

 

The mainstream though is that the Universe expanded very very rapidly already at the initial moment of the Big Bang. For instance the emitting locations of the Cosmic Microwave Background Radiation, that is the oldest remnant of the Big Bang that we can observe, was receding away from us with speeds greater than 56 times the speed of light when it emitted those photons that we recieve today. (...)

 

(bolded mine)

Reversely, doesn't that mean that we are receding from those oldest remnants at speed greater than 56 times the Speed Of Light?

[Spyman]

Reversely, doesn't that mean that we are receding from those oldest remnants at speed greater than 56 times the Speed Of Light?

Was not are, but otherwise yes, if some intelligent aliens in a very distant galaxy at around 46 billion lightyears distant are looking in our direction, then they see our part of their observable CMBR receding away from them at 56 times lightspeed.

[michel123456]

Was not are, but otherwise yes,

we agree so far.

 

if some intelligent aliens in a very distant galaxy at around 46 billion lightyears distant are looking in our direction, then they see our part of their observable CMBR receding away from them at 56 times lightspeed.

The situation is not symmetric.

An alien on that very distant galaxy looking in our direction will observe something that is 46 billion years in his past. He cannot observe us that are 46 billion years in his future. If you go out and wave your hand to the stars, only aliens that are in our future will be able to see you sometimes, eventually.

 

 

[Civat]

Intresting read! Thanks for sharing this

[Spyman]

The situation is not symmetric.

An alien on that very distant galaxy looking in our direction will observe something that is 46 billion years in his past. He cannot observe us that are 46 billion years in his future. If you go out and wave your hand to the stars, only aliens that are in our future will be able to see you sometimes, eventually.

I consider the situation symmetric, maybe I didn't express myself clearly, what I meant to say is that an alien in the distant galaxy looking in our direction will see a similar CMBR that we see, they would see our part of the Universe as it was back then around 13 billion years ago, just like we see their part of the Universe as it was around 13 billion years ago.

 

The alien can not view the Earth or me waving my hand and we can not see him waving his tentacle because it takes time for light to travel the distance between us and if space continues to expand with an accelerating rate then we will never be able to see each others.

 

Also you seem to be confusing distance with time, with an expanding Universe they are not equal. The distant galaxy with the alien is now 46 billion lightyears distant but the light we see today from that part of the Universe was emitted from a distance of only 0.04 billion lightyears around 13 billion years ago.

[ox1111]

This is a little bit of a trick question. When they see the universe is expanding at an increasing rate they are saying that it is increasing by an expanding rate relative to object around. On a side note what most scientists seem to neglect is that speed is relative to mass. For instance if you are a planet in an empty universe whatever speed you are traveling at is zero, you could theoretically be traveling at 1 million times lightspeed but no other mass or matter to relate to, your speed would be zero.

Lightspeed barrier is also a myth. Modern science is learning that there is many particles that may break lightspeed even by multiple times in graviton being one of them.

[ACG52]

This is a little bit of a trick question. When they see the universe is expanding at an increasing rate they are saying that it is increasing by an expanding rate relative to object around. On a side note what most scientists seem to neglect is that speed is relative to mass. For instance if you are a planet in an empty universe whatever speed you are traveling at is zero, you could theoretically be traveling at 1 million times lightspeed but no other mass or matter to relate to, your speed would be zero.

 

Lightspeed barrier is also a myth. Modern science is learning that there is many particles that may break lightspeed even by multiple times in graviton being one of them.

 

When cosmologist say that the expansion of the universe is accelerating, they mean it is expanding faster now than it was in the past.

 

And yes, all velocity is relative, but the rate of expansion is not the same as movement through space. Expansion is just that, the creation of more space between all non-gravitationally bound objects. The more space there is between objects, the more space is created and so the farther an object is, the faster the object appears to be moving away. At a certain distance, space is being created faster than light can travel through it, and so we say that it's expanding faster than light. But nothing is actually moving through space faster than light.

 

Your last sentence is just completely wrong.

[SomethingToPonder]

Was not are, but otherwise yes, if some intelligent aliens in a very distant galaxy at around 46 billion lightyears distant are looking in our direction, then they see our part of their observable CMBR receding away from them at 56 times lightspeed.

 

So also if intelligent aliens were looking at us from around 46 billion light years away then would we not presume they would be seeing us in the past due to the amount of time it takes for our light to reach them?

they would be seeing a non advanced civilization maybe even iron age or something. depends though they might have more advanced telescope technology which filters out the "time through visual" effect

[michel123456]

 

So also if intelligent aliens were looking at us from around 46 billion light years away then would we not presume they would be seeing us in the past due to the amount of time it takes for our light to reach them?

they would be seeing a non advanced civilization maybe even iron age or something. depends though they might have more advanced telescope technology which filters out the "time through visual" effect

Yes.

If the aliens Spyman is suggesting are living in the same time frame than we are, looking in our direction they see us as we were in the past. IOW they see nothing because the Earth was not there yet.

 

Also, if we had the chance to observe aliens in our telescope, that would be aliens "in the past". Communication would be difficult because in their telescope looking at us they would observe us in their past too, so they see dinosaurs at best. If I understand correctly.

[Spyman]

 

So also if intelligent aliens were looking at us from around 46 billion light years away then would we not presume they would be seeing us in the past due to the amount of time it takes for our light to reach them?

they would be seeing a non advanced civilization maybe even iron age or something. depends though they might have more advanced telescope technology which filters out the "time through visual" effect

According to our standard model of space expansion, intelligent aliens that are around 46 billion light years away today would see our part of the Universe as it was in the past around 13 billion years ago.

 

That is a long time before our Sun and Earth was formed and very close to when the Universe itself started, they would only see the Cosmic Microwave Background Radiation that was released from our area of the Universe during the Recombination epoch.

[alpha2cen]

 

So also if intelligent aliens were looking at us from around 46 billion light years away then would we not presume they would be seeing us in the past due to the amount of time it takes for our light to reach them?

they would be seeing a non advanced civilization maybe even iron age or something. depends though they might have more advanced telescope technology which filters out the "time through visual" effect

This is a calculated result from the contant accelerating universe model.

http://blogs.scienceforums.net/alpha2cen/2012/12/13/constant-accelerating-universe-mathematical-solution-for-the-telescope-observer/

[michel123456]

According to our standard model of space expansion, intelligent aliens that are around 46 billion light years away today would see our part of the Universe as it was in the past around 13 billion years ago.

 

That is a long time before our Sun and Earth was formed and very close to when the Universe itself started, they would only see the Cosmic Microwave Background Radiation that was released from our area of the Universe during the Recombination epoch.

Bolded mine.

 

So you say that an alien 46 BY away does not see the same thing in the sky as we do. That is in contradiction with the cosmological principle.

[Dekan]

This business of the "Cosmological Principle" seems hard to grasp. If I understand it right, it means that the Universe looks the same, from any point within it.

 

So whether you're standing here, in our Milky Way galaxy, or in the M31 Andromeda Galaxy, or in the remotest galaxy our telescopes can detect - it makes no difference. The Universe always looks the same to you. In all directions.

 

But does that make sense. If the Big Bang theory is true, the Universe started from a single, central point.

A point containing all the stuff, or matter, available.

 

Then the point exploded - flinging all the matter outwards, in an expanding sphere. The sphere must have an outer surface.

 

Suppose you were at this outer surface. Then, if you looked further outwards, you'd see nothing - just a void. Whereas if you looked inwards, you'd see all the matter within the sphere - the already formed stars and galaxies.

So you'd perceive the "Big Bang" Universe differently - according to whether you looked inwards, or outwards.

Thus violating the Cosmological Principle.

 

So is the Cosmological Principle compatible with "Big Bang" - doesn't it require a "Steady State" theory?

Edited January 10, 2013 by Dekan

[ACG52]

If the Big Bang theory is true, the Universe started from a single, central point.

A point containing all the stuff, or matter, available.

 

Then the point exploded - flinging all the matter outwards, in an expanding sphere. The sphere must have an outer surface.

 

 

 

The Big Bang was not an explosion from a central point propelling matter outward in a sphere. The BB is the expansion of every point in space from every other point. Every point in space is 'moving' away from every other point in all directions (outside of gravitationally bound entities). There is no center, and there is no outer edge.

[Dekan]

Thanks ACG52. But that can't be right, can it?

I mean, if the Universe started as a very small point, then got bigger, it must be expanding in an outwards direction.

How could it expand inwards - wouldn't that make it shrink.

 

Surely all the matter in an expanding Universe must be moving outwards.

Edited January 10, 2013 by Dekan

[ACG52]

_{Thanks ACG52. But that can't be right, can it?}

I mean, if the Universe started as a very small point, then got bigger, it must be expanding in an outwards direction.

How could it expand inwards - wouldn't that make it shrink.

 

Surely all the matter in an expanding Universe must be moving outwards.

 

_{Nope, it is right. The universe is all there is. There is no outwards direction. There is no inwards direction. It does get bigger, but not because everything is moving away from a central point, but because everything is moving away from everything else.}

 

_{When we observe the universe, we see it expanding evenly in all directions. If there were a central point to the universe, the only way we would see what we do is if we occupied that central point.}

[alpha2cen]

 

But does that make sense. If the Big Bang theory is true, the Universe started from a single, central point.

A point containing all the stuff, or matter, available.

 

So is the Cosmological Principle compatible with "Big Bang" - doesn't it require a "Steady State" theory?

This is a calculated result from the one point expansion model.

At that model, we can see the supercluster moving speed exceeds the speed of light.

http://blogs.scienceforums.net/alpha2cen/2012/12/16/one-point-accelerating-universe-calculated-results/

And, This is a calculated result from the steady state theory by using the modified Leer-Lambert law.

We can see the model does not match well up with the red shift data.

http://blogs.scienceforums.net/alpha2cen/2012/12/27/modified-beer-lambert-law-and-steady-state-universe-model/

[michel123456]

I consider the situation symmetric, maybe I didn't express myself clearly, what I meant to say is that an alien in the distant galaxy looking in our direction will see a similar CMBR that we see, they would see our part of the Universe as it was back then around 13 billion years ago, just like we see their part of the Universe as it was around 13 billion years ago.

 

The alien can not view the Earth or me waving my hand and we can not see him waving his tentacle because it takes time for light to travel the distance between us and if space continues to expand with an accelerating rate then we will never be able to see each others.

 

Also you seem to be confusing distance with time, with an expanding Universe they are not equal. The distant galaxy with the alien is now 46 billion lightyears distant but the light we see today from that part of the Universe was emitted from a distance of only 0.04 billion lightyears around 13 billion years ago.

Bolded mine.

 

Say you are living on that planet 13 BY ago.

You say that a galaxy that is 0,04 BLY from you emits a ray of light. This ray of light will reach you in 13 BY (and not in 0,04 BY)

 

You are observing a quite different universe, aren't you?

[imatfaal]

!

Moderator Note

 

alpha2cen

 

Stop advertising your own blog and ideas as answers to mainstream physics questions.

 

[alpha2cen]

!

Moderator Note

 

alpha2cen

 

Stop advertising your own blog and ideas as answers to mainstream physics questions.

 

In practice, I have not found any reference about these questions.

How to explain the incorrectness of one point expansion model, and the inequity of the steady state Universe?

I only explain it is difficult to find incorrectness in the main stream theory .

I have no intention of advertising my blog.

At any rate, I will not do it again.

[Spyman]

Bolded mine.

 

So you say that an alien 46 BY away does not see the same thing in the sky as we do. That is in contradiction with the cosmological principle.

No, I am saying that they would see a similar thing in the sky as we do which is in concordance with the cosmological principle.

 

Why do you think the bolded part of what I said is contradicting the cosmological principle?

 

 

Bolded mine.

 

Say you are living on that planet 13 BY ago.

You say that a galaxy that is 0,04 BLY from you emits a ray of light. This ray of light will reach you in 13 BY (and not in 0,04 BY)

 

You are observing a quite different universe, aren't you?

Yes, the Universe was very very different around 13 billion years ago when the CMBR we see today was emitted.

 

Modern cosmology features a changing universe that develops and ages, a backwards time traveller would see a younger Universe.

[michel123456]

No, I am saying that they would see a similar thing in the sky as we do which is in concordance with the cosmological principle.

 

Why do you think the bolded part of what I said is contradicting the cosmological principle?

 

 

Yes, the Universe was very very different around 13 billion years ago when the CMBR we see today was emitted.

 

Modern cosmology features a changing universe that develops and ages, a backwards time traveller would see a younger Universe.

 

So every alien we se today on billion of galaxies are observing a different (younger) universe than we do. The cosmological principle states that they should observe the same thing as we do, not "the same universe younger or older", but the same universe.

 

In fact I guess (putting words in your mouth) that you assume that all those aliens are today somewhere else in other places and time where they observe the same thing than we do. But you are forgetting those other aliens that died billion years ago and for which the cosmological principle should work. Nobody has ever stated that the cosmological principle is valuable only in the same time frame.

As a reminder: (from Wiki)

The cosmological principle is usually stated formally as 'Viewed on a sufficiently large scale, the properties of the Universe are the same for all observers.' This amounts to the strongly philosophical statement that the part of the Universe which we can see is a fair sample, and that the same physical laws apply throughout. In essence, this in a sense says that the Universe is knowable and is playing fair with scientists.