Size of Universe

Paul Charles William Davies, AM (born 22 April 1946) is an English physicist, writer and broadcaster, a professor at Arizona State University as well as the Director of BEYOND: Center for Fundamental Concepts in Science. He is affiliated with the Institute for Quantum Studies at Chapman University in California. He has held previous academic appointments at the University of Cambridge, University College London, University of Newcastle upon Tyne, University of Adelaide and Macquarie University. His research interests are in the fields of cosmology, quantum field theory, and astrobiology.

He has two things (partly) named after him:

The Fulling–Davies–Unruh effect is the prediction that an accelerating observer will observe black-body radiation where an inertial observer would observe none. In other words, the background appears to be warm from an accelerating reference frame; in layman's terms, a thermometer waved around in empty space, subtracting any other contribution to its temperature, will record a non-zero temperature. The ground state for an inertial observer is seen as in thermodynamic equilibrium with a non-zero temperature by the uniformly accelerated observer.

The Bunch–Davies vacuum or Euclidean vacuum: in quantum field theory in curved spacetime, there is a unique quantum state over a background de Sitter space which is invariant under all the isometries. This is a thermal state, which is at the de Sitter temperature of T = H/2pi where H is the Hubble constant.

The position that Davies takes about infinite universes, etc, reminds me of the dictum of Ludwig Wittgenstein, namely that "whereof one cannot speak thereof one must be silent", by which he meant, I think, to point to the limitations of language, and to say that merely because something may be said, it is not necessarily a meaningful locution. He is suggesting that, rather than to speak volumes of nonsense which involve using language in meaningless forays, it would be better to remain silent. Most of theology falls into this category, for it is based on unprovable and probably false underlying claims about reality.

I think speculation about whether, in an "infinite" universe, there are planets in which an identical Dale and an identical Contrex are sitting at their identical computers, only Dale has a different pullover, or they are using a language called Jugglish, or whatever, falls into the category of unprovable speculation.

Because???

Thanks Con for that report. I see that I'm amongst the elite

Tho of course not necessarily one of 'em

Intriguing speculation. My primary Q is one mathematical: Assuming the rules are the same everywhere in an infinite Universe, at any one moment wouldn't there be an infinite number of each and every possible version

Yes, probably, but to summarise Davies, so what?

Dunno, some ideas insult the intuition

Like much of modern physics. My point is, if you don't like to think about myriad worlds in which copies of you are Nobel prizewinners or notorious criminals, then you don't have to.

In fact Con I don't. I'm assuming an obscure mathematical discovery regarding infinity, which states that according to the principal that there are different kinds of infinity, I suppose an infinite Universe might contain no close simulacrums

According to the big bang theory, the universe was created from nothing, and according to mathematical computations based on relativility theory along with observations done in 1930's, the universe is expanding. Why one can't not conclude that the universe is finite?!

Wouldn't that assume that the earth sits at the very centre?

Contrex has already noted that the radius of the observable universe is about 46 billion years.

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

According to calculations, the comoving distance (current proper distance) to particles from the CMBR, which represent the radius of the visible universe, is about 14.0 billion parsecs (about 45.7 billion light years), while the comoving distance to the edge of the observable universe is about 14.3 billion parsecs (about 46.6 billion light years),[1] about 2% larger.

Yea Hakim, one might ask, if it's expanding how can it be infinite

http://able2know.org/topic/260015-1

Well Wislo, yes and no. Anyone anywhere presumably can assume he is at the center

Yes Kn as I had acknowledged earlier mine was sheer speculation

Since the "observable universe" is what we can see from earth, the earth is by definition at the centre of it. We have no knowledge of any other parts of the universe.

My understanding is as follows. If a reader spots any errors and chooses to enlighten me about them, I shall be grateful.
I assume that the energy of the matter in the universe is exactly balanced by the gravitational potential energy. In this case, M*c^2 = G*M^2/R, where M is mass in kg (8.7895e52), c is the velocity of light 299,792,458 m/s, G is the gravitational constant 6.67384e-11 N*m^2/kg^2, and R is the radius of the universe in meters. If the equation is solved for R, we obtain R = G*M/c^2 = 6.5268e25 meters. This is the radius of the universe. Note that this value is exactly half the Schwarzchild radius of the universe, which is defined as Rs=2*G*M/c^2 and turns out to be 1.3054e26 meters.
All this depends on the mass being 8.7895e53 kg. This value is obtained from the critical density assuming a flat universe, and the volume. The critical density for a flat universe is Vc = 3*H^2/(8*pi*G) = 9.434e-27 kg/m^3. H is the Hubble constant and G the gravitational constant. The Hubble constant can be taken as 1/s where s is the age of the universe in seconds.
The volume of the universe to be used in this formula is the volume of a sphere with a radius of 13.798e9 light years, and is 3.566e80 m^3. Because of the expansion of space, the actual radius in light years is about 46.5e9 light years. Therefore space is expanding 3.2 times light speed.

You're smarter than me

Quite an assumption isn't it?

It seems to me that the zero-energy universe is a logical necessity. I was introduced to this idea from the “Hidden in Plain Sight” trilogy by Andrew Thomas (www.ipod.org.uk/reality/index.asp). Thomas says it originated in 1973, when Edward Tryon proposed in the Nature journal that the Universe may have emerged from a large-scale quantum fluctuation of vacuum energy, resulting in its positive mass-energy being exactly balanced by its negative gravitational potential energy.
Stephen Hawking advocates the zero-energy universe. He notes in his 2010 book The Grand Design:
"If the total energy of the universe must always remain zero, and it costs energy to create a body, how can a whole universe be created from nothing? That is why there must be a law like gravity. Because gravity is attractive, gravitational energy is negative: One has to do work to separate a gravitationally bound system, such as the earth and moon. This negative energy can balance the positive energy needed to create matter, but it’s not quite that simple. The negative gravitational energy of the earth, for example, is less than a billionth of the positive energy of the matter particles the earth is made of. A body such as a star will have more negative gravitational energy, and the smaller it is (the closer the different parts of it are to each other), the greater the negative gravitational energy will be. But before it can become greater than the positive energy of the matter, the star will collapse to a black hole, and black holes have positive energy. That’s why empty space is stable. Bodies such as stars or black holes cannot just appear out of nothing. But a whole universe can." (p. 180)
The reason that a whole universe can appear out of nothing is expressed in the Heisenberg uncertainty principle. This requires that particles must continually appear out of nothing then vanish, according to:
ΔT * ΔE ≤ ћ/2 ≈ 1.6784E-35 Joule-seconds
The first term, ΔT, is the time duration that the particle exists; the term ΔE is the energy of the created particle, and ћ is the reduced Planck constant. This decrees that empty space must randomly teem with all possible virtual particles and their anti-particles; they pop into existence for a time that must be less than a constant divided by the energy of the virtual particle. When their time is up, the particles and anti-particles self annihilate, paying back the energy that went into their production.
Note that the formula for the uncertainty principle says that if ΔE is zero, then ΔT is unbounded. This means that even an immense particle, such as our universe, can come into existence forever as long as its energy, ΔE, is zero.

Now it seems you are trying to hide behind the mathematics.
Not even a yota of an mathematical equations can make nothing exploding in something. Tru doing it one day! LOL
You see, you need ALWAYS keep in line with what you are doing with math.
In tis case you have used Math in an inproper way, hence the outcome is improper and illogical. Nobody impresses me with their math, I do know a lot about tensor calculus, calculus, diif equations and such.
Furthermore, the mathematics used is very unreliable.(like Calculus)
Just drop the math and start real critical thinking.
And btw Stephen hawking is a liar an a cheat. But I won't be to harsh on him because he is used by Intelligence agencies to fool us all!.
Really, mainstram physics is bollocks and shite blinged together!