Finite or Infinite?

[addicted-]

Is the Universe finite or infinite? What do you think?

The universe could be infinite, or possibly finite
Either way the universe would have no center or boundaries
If it was finite an object traveling off in one direction would
eventually re-appear.

Only thing that is certian is that the Universe is expanding.

[coldcreation]

Originally Posted by addicted-

Is the Universe finite or infinite? What do you think?

The universe could be infinite, or possibly finite
Either way the universe would have no center or boundaries
If it was finite an object traveling off in one direction would
eventually re-appear.

Only thing that is certian is that the Universe is expanding.

"We see that at immense distances there are more of such star-systems [galaxies], and that the creation in all the infinite extent of its vastness is everywhere systematic and related in all its members…The plan of their revelation must therefore, like themselves, be infinite and without bounds.” (Kant 1755, 1969, p. 63-65)

Bear in mind, the Riemannian multi-dimension spaces of constant positive curvature (this is not observed in the real world) are precisely what led to the globally homogenous spherically symmetrical finite universe with an attitude: the infamous boundary condition.

Consider, now, the simplest example of an isotropic two-dimensional curved space, namely the surface of a hyperbolic manifold. This two-space is isotropic because the degree of curvature is the same at all points in the two-space (shaped like the surface of a saddle, or a Pringles potato-chip). If we extend our model to three spatial dimensions we are no longer looking at a saddle shape; we have the curved volume of a hyperspher (see the SNe Ia data).

The fourth associated dimension, the temporal coordinate, varies proportionally with the curvature of the three-dimensional volume. We are in possession of a four-dimensional singularity-free non-expanding, non-contracting continuum, the physical attributes of which are described by general relativity and are observed in nature.

Note, regarding your last phrase above: The only thing certain in cosmology is that very few things are proved beyond reasonable doubt. Expansion is not one of them.

CC




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[Buffy]

addicted-, I'd like to introduce you to coldcreation. cc disagrees with most of what you know about cosmology....

Originally Posted by coldcreation

Note, regarding your last phrase above: The only thing certain in cosmology is that very few things are proved beyond reasonable doubt. Expansion is not one of them.

"Beyond reasonable doubt" of course is a legal rather than scientific phrase, and to me its an interesting way to haughtily dismiss widely accepted theories as "unproven." That's a "true" statement, but its irrelevant in *supporting* less well-accepted alternative theories: they have to stand--or fall--on their own....

I think its fair to say that the question in the original post does make the assumption that the conventional wisdom regarding BB is true, and *given* that, is the Universe finite or infinite. If you want to beat your drum on SSU, cc, please do it elsewhere....

Expanding discussions by not overloading them,
Buffy

[coldcreation]

Originally Posted by Buffy

addicted-, I'd like to introduce you to coldcreation. cc disagrees with most of what you know about cosmology....

"Beyond reasonable doubt" of course is a legal rather than scientific phrase, and to me its an interesting way to haughtily dismiss widely accepted theories as "unproven." That's a "true" statement, but its irrelevant in *supporting* less well-accepted alternative theories: they have to stand--or fall--on their own....

I think its fair to say that the question in the original post does make the assumption that the conventional wisdom regarding BB is true, and *given* that, is the Universe finite or infinite. If you want to beat your drum on SSU, cc, please do it elsewhere....

Expanding discussions by not overloading them,
Buffy

Thank you Buffy for the introduction. Just to set the record straight, let's say that I remain open to alternative explanations for redshift z. And so the idea that expansion is real may be erroneous, as Hubble himself had suspected. Hence the phrase "Only thing that is certian is that the Universe is expanding" needed to be corrected. The fact is, expansion has never been certain.

Why is this important on the topic of whether the universe is infinite of not?

The coiling of time and space around itself, near a big bang event, leads to a theoretical possibility and physical impossibility of an observer experiencing his own past—a notion inconsistent with a fundamental description of nature, the arrow of time (irreversibility). It is precisely this contempt for explanations that lay behind Einstein’s scepticism of the big bang singularity. Thus, the question of understanding it simply did not concern him, except as something to dismiss.

He certainly did understand the enigmatic inscriptions encoded in the equations and the complicated liaisons they had with nature, but he also realized their predisposition in the direction of abstraction. For this reason Einstein’s obduracy towards the synthetic concept of spacetime singularities was clear enough.

Yes, Einstein’s static universe had a constant positive curvature and was spatially closed, temporally infinite (or “finite yet unbounded”), the scale factor or radius remaining constant with time. ‘Infinite,’ here refers to the continuous curvature of spherical space. Note that had time not been considered infinite the universe would posses a central symmetry. Both Einstein and de Sitter realized a four-dimensional sphere had the bizarre feature of allowing the coiling of time around itself, leading to the hypothetical prospect of an observer experiencing his own past. The physical meaning of the spherical model prompted de Sitter’s hyperboloid solution, avoiding the time paradox by leaving open the time direction.

It is the latter solution to the field equations to which I adhere. Note, Buffy, that the de Sitter space carries with it a redshift that increases with distance in a static universe, precisely what Hubble thought operational in the real world. His Doppler calculations for z were strictly for convenience.

See, for example:

Hubble, E. 1929, A Relation Between Distance and Radial Velocity Among Extra-Galactic Nebula, From Field, G.B., Arp, H., Bahcall, J.M. 1973, The Redshift Controversy 173

Hubble, E. 1936, The Realm of the Nebula 108-201

CC

[sanctus]

But colcreation, don't most measures today point to an universe with critical density and hence flat and hence infinite?

[coldcreation]

Originally Posted by sanctus

But colcreation, don't most measures today point to an universe with critical density and hence flat and hence infinite?

To arrive at a critical density 96% of the constituents of the universe have to be dark, nondetectable, chimerical.

A flat universe would have been nice, yes indeed, then, inflation would have met one prediction correctly, and the favored Friedmann model (the critical one) would have passed a major test. Unfortunately that is not what is observed.

See the SNe Ia data. The universe is infinite yes (at least it can be extrapolated to be so), but is is about 25% off the mark as far as flatness. That is why the post-1998 standard model has only 4% real matter (i.e., in baryonic form) and energy.

A+



CC

[sanctus]

yes almost agree, not on the non-detectability of dark energy and matter, they are detectable indirectly for example rotation speeds of stars when approaching the outer limit of a galaxy...

[coldcreation]

Originally Posted by sanctus

yes almost agree, not on the non-detectability of dark energy and matter, they are detectable indirectly for example rotation speeds of stars when approaching the outer limit of a galaxy...

True, but it should be made clear the distinction between baryonic dark matter (made of protons, neutrons, electrons).

We know that dark matter exists in the form of faint objects—collectively referred to as brown dwarfs. These are low luminosity objects that are very difficult to detect because they are very weak emitters of electromagnetic radiation, e.g. low mass stars that no longer burn hydrogen into helium. Other examples of dark matter include planets, comets, asteroids, rocks, dust, and gas.

From application of the viral theorem to the rotational curves of galaxies and clusters, estimations of the dark matter are about ten times that of visible matter. This dark matter is thought to be responsible for the binding of galaxies and galactic clusters (Longair 1993). We are still 2 orders of magnitude less than the critical value (for the favored ? = 1 Friedmann model) let alone the ? > 1 model. Fortunately, a deceleration in the rate of expansion is not detected observationally. Thus, the need to introduce something nonbaryonic.


Note: There is also another way to arrive at those velocities (unfortunately, beyond the scope of this thread).

So what is thought to be indirect evidence in favor of something spurious could very well be direct evidence of something else entirely (hint: no new physics is required).


A bientot


CC

[coldcreation]

Originally Posted by Buffy

..."Beyond reasonable doubt" of course is a legal rather than scientific phrase, and to me its an interesting way to haughtily dismiss widely accepted theories as "unproven." That's a "true" statement, but its irrelevant in *supporting* less well-accepted alternative theories: they have to stand--or fall--on their own....
...Buffy

I just found an interesting article on BBC here (after having seen a news flash about it on BBC World).

"Dr Andy Bunker is a high-redshift hunter with Exeter University, UK. He has worked with the Ellis group in the past but was not involved in this study.

He commented: "Richard is a careful worker and he knows the burden of proof is very high."

Beyond reasonable doubt and burden of proof are commonly used both is the domains of law as well as in science (there are many other examples).

That having been said (written) the article sheds light (pun non-intented) on the earliest galaxies observed to date. The age of these galaxies pushes the so-called dark ages back a few years.

Hopefully, with help from the James Webb Space Telescope, presumably scheduled for launch after 2011, many more old, massive, well-formed galaxies will be discovered, pushing back the dark ages indefinately. Thus the JWST should make or break the standard canonical hot big bang cold-dark-matter-dark-energy model.

CC

[Buffy]

Originally Posted by coldcreation

He commented: "Richard is a careful worker and he knows the burden of proof is very high."

Beyond reasonable doubt and burden of proof are commonly used both is the domains of law as well as in science (there are many other examples).

You're still conflating dear (excuse the pun! )...

The quote says nothing about "beyond reasonable doubt": I will grant it is used colloquially in scientific discussions, but its use is colloquial. There is no scientific definition of "reasonable doubt" only varying gradations of general acceptance: fundamental to the scientific method is the notion that it is *always* possible that a new discovery will upend even the most "certain" theories, and thus the notion that anything is "beyond doubt" is by *definition* unscientific.

There's of course nothing wrong with "burden of proof" although while being less egregious, is still bending the notion of "proof" to be "supporting data" which is similar to the notion of "evidence" as used in the legal profession.

I don't mind this much except for situations where people try to bend these terms in order to devalue *science*, something of which I know you are not guilty!

Enjoying the (data-supported and pun-encrusted) expansion of the universe,
Buffy