The Universe expanding at the speed of light?

[Spyman]

 

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.

Both humans and hypothetical aliens in the past viewed the Universe in a different age than what we do today.

 

The cosmological principle is NOT in conflict with the Big Bang theory, you are misinterpreting it.

 

Did you even read what your Wikipedia link about the cosmological principle said under Implications?

 

The universe is now described as having a history, starting with the Big Bang and proceeding through distinct epochs of stellar and galaxy formation. Because this history is currently described (after the first fraction of a second after the origin) almost entirely in terms of known physical processes and particle physics, the cosmological principle is extended to assert the homogeneity of cosmological evolution across the anisotropy of time:

 

... all points in space ought to experience the same physical development, correlated in time in such a way that all points at a certain distance from an observer appear to be at the same stage of development. In that sense, all spatial conditions in the Universe must appear to be homogeneous and isotropic to an observer at all times in the future and in the past.

 

That is, earlier times are identical to the "distance from the observer" in spacetime, which is assessed as the redshift of the light arriving from the observed celestial object: the cosmological principle is preserved because the same sequence of evolution is observed in all directions from earth, and is inferred to be identical to the sequence that would be observed from any other location in the universe.

/../

Cosmologists agree that in accordance with observations of distant galaxies, a universe must be non-static if it follows the cosmological principle. In 1923, Alexander Friedmann set out a variant of Einstein's equations of general relativity that describe the dynamics of a homogeneous isotropic universe. Independently, Georges Lemaître derived in 1927 the equations of an expanding universe from the General Relativity equations. Thus, a non-static universe is also implied, independent of observations of distant galaxies, as the result of applying the cosmological principle to general relativity.

http://en.wikipedia.org/wiki/Cosmological_principle

[michel123456]

I disagree with the Wiki article: it is an attempt to conciliate the unconciliatables.

 

It is written:

 

 

the cosmological principle is preserved because the same sequence of evolution is observed in all directions from earth, and is inferred to be identical to the sequence that would be observed from any other location in the universe.

Bolded mine.

 

The word "sequence" has been added artificially to the C.P. in order to fit with the BBT.

There is no "sequence" word in the C.P.

 

The BBT states that we are living in a special epoch of the Universe. It also states that all observers far from us (and thus in the past) observe different things than we do. BBT states that an observer on Earth a few billion years ago could observe a more dense universe than we do. The Theory also states that in the far future an observer on Earth will observe a universe more dissipated.

 

IOW the BBT states that the place & time of the observer determines what he will observe. There are even some scientists that argue that in the far future an observer would see a totally different universe. (see below)

 

 

From here: (Lawrence Krauss On 'A Universe From Nothing'

January 13, 2012 1:00 PM) - Bolded mine.

 

 

 

FLATOW: 1-800-989-8255. You mentioned in your book that we are lucky to be living in this time in the universe.

 

KRAUSS: Yeah, I mean for a variety of reasons. One is in the far future, and by the far future I mean hundreds of billions of years, astronomers and radio hosts on planets around other stars will look out at the universe, and what they'll see is the universe we thought we lived in 100 years ago, all of the other galaxies will have disappeared expect for our own, and people will assume, or beings will assume, they live in a universe that's basically infinite, dark and empty except for one galaxy, with no evidence of the Big Bang.

 

 

I don't consider that all this is compatible with the C.P.

[Spyman]

I disagree with the Wiki article: it is an attempt to conciliate the unconciliatables.

 

/../

 

The BBT states that we are living in a special epoch of the Universe. It also states that all observers far from us (and thus in the past) observe different things than we do. BBT states that an observer on Earth a few billion years ago could observe a more dense universe than we do. The Theory also states that in the far future an observer on Earth will observe a universe more dissipated.

 

IOW the BBT states that the place & time of the observer determines what he will observe. There are even some scientists that argue that in the far future an observer would see a totally different universe.

 

/../

 

I don't consider that all this is compatible with the C.P.

Well Michel, this is clearly your own personal opinion and not the conventional interpretation made by mainstream scientists.

 

Furthermore you are muddling the truth with false claims to make your argument sound better than what it actually is:

* The Big Bang theory does NOT state that we are living in a special epoch. It says that we are living in a different epoch than how it was in the past and that the future will bring new times. There is no claims on anything special about our current epoch.

* The Big Bang theory does NOT state that observers far from us observe different thing than we do. It says that all observers, including us right here, would have observed different things in the past. There is no claims that far from us observers are in the past.

* The Big Bang theory does NOT state that the place of the observer in space determines what he will observe. It says that the Universe has evolved from a hot and dense state to this cold expanding state it currently is in. Observers in different ages will see different stages of this development, but there is no claims on special locations with special views.

* It is NOT only some few scientists that think the future will look different. This is the mainstream scientific consensus, which means that most professional scientists in the field of cosmology together have made a collective judgement of this.

 

A well versed and experienced member like you should know that when you want to propose that the ordinary cosmological principle should be changed to a more specialized variant, argue that the currently accepted Big Bang theory is wrong or speculate about obsolete Steady State theories, then this is best done by creating a new thread in the Speculations section and not by hijacking a thread in the Astronomy section where people expects answers in concordance with mainstream scientific consensus.

Edited January 15, 2013 by Spyman

[J.C.MacSwell]

In a "perfect world" the perfect cosmological principal would hold:

 

http://en.wikipedia.org/wiki/Perfect_cosmological_principle

 

 

The Perfect Cosmological Principle states that the Universe is homogeneous and isotropic in space and time. In this view the universe looks the same everywhere (on the large scale), the same as it always has and always will. It is the principle underpinning steady-state theory and emerging from Chaotic inflation theory.^[1][2][3]

The Perfect Cosmological Principle is an extension of the Cosmological Principle, which accepts that the universe changes its gross feature with time, but not across space.

[michel123456]

In a "perfect world" the perfect cosmological principal would hold:

 

http://en.wikipedia.org/wiki/Perfect_cosmological_principle

 

 

The Perfect Cosmological Principle states that the Universe is homogeneous and isotropic in space and time. In this view the universe looks the same everywhere (on the large scale), the same as it always has and always will. It is the principle underpinning steady-state theory and emerging from Chaotic inflation theory.^[1][2][3]

 

The Perfect Cosmological Principle is an extension of the Cosmological Principle, which accepts that the universe changes its gross feature with time, but not across space.

Wonderful, I didn't know it had a name.

The talk page is better than the article.

 

Well Michel, this is clearly your own personal opinion and not the conventional interpretation made by mainstream scientists.

 

Furthermore you are muddling the truth with false claims to make your argument sound better than what it actually is:

* The Big Bang theory does NOT state that we are living in a special epoch. It says that we are living in a different epoch than how it was in the past and that the future will bring new times. There is no claims on anything special about our current epoch.

* The Big Bang theory does NOT state that observers far from us observe different thing than we do. It says that all observers, including us right here, would have observed different things in the past. There is no claims that far from us observers are in the past.

* The Big Bang theory does NOT state that the place of the observer in space determines what he will observe. It says that the Universe has evolved from a hot and dense state to this cold expanding state it currently is in. Observers in different ages will see different stages of this development, but there is no claims on special locations with special views.

* It is NOT only some few scientists that think the future will look different. This is the mainstream scientific consensus, which means that most professional scientists in the field of cosmology together have made a collective judgement of this.

 

A well versed and experienced member like you should know that when you want to propose that the ordinary cosmological principle should be changed to a more specialized variant, argue that the currently accepted Big Bang theory is wrong or speculate about obsolete Steady State theories, then this is best done by creating a new thread in the Speculations section and not by hijacking a thread in the Astronomy section where people expects answers in concordance with mainstream scientific consensus.

(bolded mine)

Let the public judge about that.

[ACG52]

Let the public judge about that.

 

 

 

Why? It's not a popularity contest. The points you listed are incorrect.

[michel123456]

 

Why? It's not a popularity contest. The points you listed are incorrect.

 

No.

 

Take it one by one. I am correct, Spyman is wrong.

what Spy should have done is to follow the the POV of the Wiki talk page: that is to decide that the BBT is correct and thus put a question mark onto the CP, and not trying to conciliate the one with the other.

 

1. Following the BBT, we are living a SPECIAL epoch in between an extremely hot beginning and an extremally cold end. That is the reason why Krauss explains that "we are lucky'. There is NOTHING NORMAL in the epoch we are living because the Universe is EVOLVING, so the is no "normal" epoch.

 

2. Observers that are 'far from us in the present" are outside our light-cone. The concept of "far from us" includes the notion of time thanks to Relativity. The concept of 'far from us in the present" (which is in the basis of the CP) relies on the concept of an universal present time. I guess that is because the CP is an extension of the Copernican Principle at a time when nobody had a clue about Spacetime. In fact, "far from us" includes time, and since only the past is observable, the only part of Time that we can include into the CP is the past. Except if you come and explain that we can observe the future.

 

3. The Big Bang theory does state that the time and place determines what one will observe. Today here I observe the actual sky. Yesterday here the dinosaurs were observing a different sky. Tomorrow here in a few billion years we will observe a different sky. Somewhere else at a different time an alien was or will observe a different sky. ONLY the aliens that are upon our supposed "universal present" are observing the same things that we do. THAT is what the BBT states.

 

4. If there are many scientists that follow the mainstream, that is not for a surprise, that is the definition of "mainstream". I know that the collective judgment is that the Universe has been created and is evolving since then. The question is not wether the BBT is right or wrong. the question is wether the BBT is compatible with the CP. Because if the BBT is correct, there is something wrong in the CP, IMHO.

Edited January 15, 2013 by michel123456

[ACG52]

Take it one by one. I am correct,

 

 

You've simply repeated your points and said 'I am correct'. You haven't made any argument to show that you're correct.

 

Your first point, that this is a 'special' time between the beginning and the end, ignores that the 'special' time is most of the lifetime of the universe. It is the norm, not the exception.

 

Your second point doesn't seem to have one. Point that is.

 

The BBT says that all points in space will see basically the same universe. Someone on a planet 10 billion lys away will see a universe that looks just like the one we see. Someone ten billion years ago would see something very different. Time matters, place doesn't.

Edited January 15, 2013 by ACG52

[Maxila]

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.

 

You appear to be more knowledgeable than most; I’ve tried to find those relationships several times before unsuccessfully. I have an unanswered question regarding the dynamics used to determine the accelerating expansion that I have been unable to find an answer too. Perhaps you can help?

 

In what I've read, they determine red shift due to the expected expansion of space relative to the luminosity of various distant supernovas. In a nutshell more distant supernova of a given redshift are dimmer than expected. I could not find if, when determining red shift for the expected expansion of space, they gave consideration to red shift for any receding physical relative velocity a more distant supernova might also have?

 

In other words wouldn't the supernova have a physical receding relative velocity that caused red shift, in addition to red shift for its distance and the expansion of space? I couldn't find any references to that dynamic in my queries, and it seemed to me that more distant supernova in a younger Universe should have a greater receding relative velocity red shift, in addition to a greater red shift for the expansion of space?

 

Maxila

[ACG52]

 

it seemed to me that more distant supernova in a younger Universe should have a greater receding relative velocity red shift,

 

 

Why would there be a larger proper velocity in a younger universe? Remember that the BB was not an explosion which imparted a velocity to things.

[Maxila]

 

Why would there be a larger proper velocity in a younger universe? Remember that the BB was not an explosion which imparted a velocity to things.

 

That's is excatly what I wondered about, after comsic inflation, I thought there was also a velocity (kinetic energy) imparted to the energy (the physical stuff) of space. I guess that answeres my question, no kinetic energy was deemed to be transfered to the physical stuff of space, right?

 

Maxila

[Spyman]

In other words wouldn't the supernova have a physical receding relative velocity that caused red shift, in addition to red shift for its distance and the expansion of space? I couldn't find any references to that dynamic in my queries, and it seemed to me that more distant supernova in a younger Universe should have a greater receding relative velocity red shift, in addition to a greater red shift for the expansion of space?

 

That's is excatly what I wondered about, after comsic inflation, I thought there was also a velocity (kinetic energy) imparted to the energy (the physical stuff) of space. I guess that answeres my question, no kinetic energy was deemed to be transfered to the physical stuff of space, right?

Supernovas do have physical relative velocities to us that affects their measured redshift, but 1) random supernovas in random directions from us have random physical velocities relative us, that is caused by the local to them environment and is therefore not increasing with the relative distance to us and 2) this physical relative velocity is normally not so high and is also limited to be below the speed of light while the expansion of space can cause receding velocities much greater than lightspeed for very distant objects, so when distances increase the rate between physical velocity and receding velocity changes such that physical velocity have lesser and lesser influence on the expected rate between redshift and distance.

 

In physical cosmology, the term peculiar velocity (or peculiar motion) refers to the components of a receding galaxy's velocity that cannot be explained by Hubble's law.

 

According to Hubble, and as verified by many astronomers, a galaxy is receding from us at a speed proportional to its distance. The relationship between speed and distance would be exact in the absence of other effects.

 

Galaxies are not distributed evenly throughout observable space, but typically found in groups or clusters, ranging in size from fewer than a dozen to several thousands. All these nearby galaxies have a gravitational effect, to the extent that the original galaxy can have a velocity of over 1,000 km/s in an apparently random direction. This velocity will therefore add, or subtract, from the radial velocity that one would expect from Hubble's law.

 

The main consequence is that, in determining the distance of a single galaxy, a possible error must be assumed. This error becomes smaller, relative to the total speed, as the distance increases.

 

A more accurate estimate can be made by taking the average velocity of a group of galaxies: the peculiar velocities, assumed to be essentially random, will cancel each other, leaving a much more accurate measurement.

http://en.wikipedia.org/wiki/Peculiar_velocity#Cosmology

 

General relativity describes spacetime by a metric, which determines the distances that separate nearby points. The points, which can be galaxies, stars, or other objects, themselves are specified using a coordinate chart or "grid" that is laid down over all spacetime. The cosmological principle implies that the metric should be homogeneous and isotropic on large scales, which uniquely singles out the Friedmann-Lemaître-Robertson-Walker metric (FLRW metric). This metric contains a scale factor, which describes how the size of the Universe changes with time. This enables a convenient choice of a coordinate system to be made, called comoving coordinates. In this coordinate system the grid expands along with the Universe, and objects that are moving only due to the expansion of the Universe remain at fixed points on the grid. While their coordinate distance (comoving distance) remains constant, the physical distance between two such comoving points expands proportionally with the scale factor of the Universe.

 

The Big Bang is not an explosion of matter moving outward to fill an empty universe. Instead, space itself expands with time everywhere and increases the physical distance between two comoving points. Because the FLRW metric assumes a uniform distribution of mass and energy, it applies to our Universe only on large scales - local concentrations of matter such as our galaxy are gravitationally bound and as such do not experience the large-scale expansion of space.

http://en.wikipedia.org/wiki/Big_Bang#FLRW_metric

[Maxila]

 

Supernovas do have physical relative velocities to us that affects their measured redshift, but 1) random supernovas in random directions from us have random physical velocities relative us, that is caused by the local to them environment and is therefore not increasing with the relative distance to us and 2) this physical relative velocity is normally not so high and is also limited to be below the speed of light while the expansion of space can cause receding velocities much greater than lightspeed for very distant objects, so when distances increase the rate between physical velocity and receding velocity changes such that physical velocity have lesser and lesser influence on the expected rate between redshift and distance.

 

That was what I was unsure of. I thought there might be a relative receding velocity for all galaxies, proportional to distance, that was in addition to their velocity due to expansion of space; I understand that is not deemed to exist now. The relative velocity you are referring too I assume is due to the local gravitational environment, which was not what I was wondering about.

 

Thank you,

Maxila

[Spyman]

I am correct, Spyman is wrong.

Everyone with a reasonable reading comprehension who have read my post #26 can see that I have presented factual consensus of mainstream science where the cosmological principle and the Big Bang theory are consistent with each others.

 

I suggest you stop repeating yourself, remove your fingers out of your ears, open up your eyes and go back to read it again.

 

[michel123456]

Everyone with a reasonable reading comprehension who have read my post #26 can see that I have presented factual consensus of mainstream science where the cosmological principle and the Big Bang theory are consistent with each others.

 

I suggest you stop repeating yourself, remove your fingers out of your ears, open up your eyes and go back to read it again.

 

I did that (i read it again but I am experiencing some difficulties to push my keyboards buttons with my elbow while having my fingers in my ears, fearing the noise of your posts in the dark)

 

My opinion is that you are reading what you want to read and not the words that are written.

 

I hope your opinion is the same: that Michel reads what he wants to read and not the words that are written.

 

In the meanwhile, please do something for me: go read again your own post #26 and ask yourself about the followings:

 

"the cosmological principle is extended"

 

"the cosmological principle is preserved because ...."

 

And the false assertion that:

 

"a universe must be non-static if it follows the cosmological principle"

 

Newton turns into his grave. Copernicus too.

[Spyman]

I hope your opinion is the same: that Michel reads what he wants to read and not the words that are written.

I am sorry Michel, but your unchangeable conviction that mainstream science regard the cosmological principle to be contradicting the Big Bang theory, is so far from any normal interpretation that I can't help you further.

 

However, facts will remain as facts, even if you disagree about them or when you are unable to understand them.