Big Bang - Where's the hole?

Originally posted by Maslo
reply to post by zeta55

 

By blowing up the baloon, with the galaxies drawn on the surface, yes all the galaxies are moving away from each other. I still conclude there is a central point.

Where on the surface of the baloon is the central point located then?

Where the balloon is blown up. You can draw a trillion dots on a balloon, blow it up to be the size of the universe, and not one dot will ever move to where you tied it off (the nozzle?).

reply to post by jiggerj


But, in the case of the universe, there is no hole through which air is being blown to inflate it.

reply to post by CLPrime


If you throw a ball in outer space, where is it going to stop?

reply to post by CLPrime

But, in the case of the universe, there is no hole through which air is being blown to inflate it.

There has to be.

Not a classical hole, mind you.

There must be some point of entry for this "dark energy." Pressure in gasses is caused by the relative excitation of molecules and their tendency to occupy additional space when in a higher energy state.

What's being driven into a higher energy state by this dark energy? What is being excited so as to exert this pressure?

reply to post by Aim64C

What's being driven into a higher energy state by this dark energy? What is being excited so as to exert this pressure?

The space itself. Thats why its called the metric expansion of space.

reply to post by AfterInfinity


Good question.
The likely answer: nowhere. It won't stop. Ever.

reply to post by Aim64C


No, there doesn't have to be. The pressure is exerted by the vacuum of space. The pressure causing the expansion exists within the surface of the sphere.

reply to post by Maslo

The space itself. Thats why its called the metric expansion of space.

"Magic" would have been a more satisfactory answer.

Quantum mechanics poses a bit of an obstacle to the very concept of space, as the quantum nature of interactions can be argued to give rise to space (particularly when considering things such as the holographic principle).

Which means that you can't change space arbitrarily. It's akin to changing the size of the squares on a chess board - it does nothing to change the game, since the game deals in squares as the only metric.

But, I'm being a little brutal for an opening salvo.

Let's start with a simple question: "What is expanding?"

Your answer: "Space is expanding."

"What is space?"

I'll return tomorrow for your answer. It's getting late, and controlling my condescending hubris is getting increasingly difficult. Take your time and actually answer the question.

reply to post by Aim64C

Which means that you can't change space arbitrarily. It's akin to changing the size of the squares on a chess board - it does nothing to change the game, since the game deals in squares as the only metric.

I think its more like adding more squares than changing their size (if we mean Planck volumes of space by squares).

reply to post by CLPrime

No, there doesn't have to be. The pressure is exerted by the vacuum of space. The pressure causing the expansion exists within the surface of the sphere.

You're talking in circles, here.

What sphere?

Perhaps more importantly - how does the vacuum of space exert pressure?

I'm not asking for your condescending, grade-school level answers to this stuff. I'm asking for a real theory - a real model.

You're reading like a book on 'faeries' - arbitrary, convenient magichanics that are self-exclusionary if not conflicting. Enough to satisfy a curious believer with surface-deep and grazing explanations.

Not enough to satisfy the hunger I have for knowledge. If you've got a model that proposes to demonstrate galactic inflation from a mechanical standpoint - you've a thing in very short supply, and I want it.

reply to post by Maslo

I think its more like adding more squares than changing their size (if we mean Planck volumes of space by squares).

Except all metrics are based off of the speed of light - an unchanging constant in all accepted physics.

Altering Planck volumes - derived from the energy quanta expressed in light, would thus seem impossible. Metric expansion of space would ultimately not change the size of the Planck volumes.

Adding more Planck volumes between objects doesn't exactly ring as any more plausible as conservation of energy would create multiple situations in which this volumetric expansion would have to be accompanied by changes of energy states that would trigger release of energy quanta and result in detectable phenomena.

Or maybe that's Einstein's "Hidden Variable" ... an intriguing possibility and somewhat ironic considering his role in the development of modern cosmology.

Originally posted by Aim64C
You're talking in circles, here.

What sphere?

Perhaps more importantly - how does the vacuum of space exert pressure?

I'm not asking for your condescending, grade-school level answers to this stuff. I'm asking for a real theory - a real model.

Okay. We can write the metric of space as ds^2 = -c^2 dt + a(t)^2 * (dr^2 + S(r)^2 do^2)
where a(t) is a variable scale factor, S is a curve parameterization (0 for flat space, +1 for positive curvature, -1 for negative curvature, depending on your model.)
dt, dr and do are the differentials of time, distance and angular size, respectively, which contribute to the distance measure ds.

From this you can see that the spatial geodesic will scale with a(t). Now, we use Einstein's field equations to find the dynamics of this metric for different arrangements of matter and energy (different stress-energy tensors.) You find that matter will tend to contract the metric, which can either have started with a sufficient "escape velocity" to expand forever, or reach a standstill, or contract, depending.

You can write down equations describing the dynamics of the scale factor accordingly. By solving these equations, you'll then have your description of how space expands or contracts depending on the density and equation of state of the fields which inhabit the space. Then you can play around adding/subtracting matter, radiation, and a cosmological constant, and see how the universe behaves.

Originally posted by Aim64C

You're talking in circles, here.

What sphere?

The sphere that everyone's been talking about since this thread began. The sphere that has a 2-dimensional version of our universe as its surface, to represent the expansion of space as the inflation of the sphere.
It's highly inaccurate, but it works (sometimes).

Perhaps more importantly - how does the vacuum of space exert pressure?

I'm not asking for your condescending, grade-school level answers to this stuff. I'm asking for a real theory - a real model.

Alrighty...

A vacuum is not a classical object. It's a quantum object, just like everything else. And a quantum vacuum is defined as the lowest possible energy level of an isolated system. The thing with quantum mechanics, however, is that things like "lowest possible" are all probabilistic. In the same way a solid object (composed of particles obeying Fermi-Dirac statistics to normally prevent passing through other particles) can, in QM, "tunnel" through another solid object with some near-infinitesimal probability, the quantum vacuum can spontaneously collapse to a lower-energy state. The potential energy represented by the change in energy level is released from the vacuum as kinetic energy. This kinetic energy is in direct opposition to the current positive energy density of the universe - that is, it exerts negative pressure on the space it fills. This is what Einstein called the Cosmological constant in his field equations. And this negative pressure, according to those same field equations (which have been so successful at describing gravitational effects), causes metric expansion.

This is the negative pressure thought to be responsible for the initial period of rapid inflation at the Big Bang. As the universe expanded, it cooled, and the inflation field experienced a change of state. This led to the positive energy density we see today, as well as forming the particles that exist. Continued expansion is possibly a result of a more limited form of the initial vacuum collapse, in accordance with the Uncertainty Principle.

The initial quantum vacuum is an example of zero-point energy.
The current expansion would be due to vacuum energy.
Essentially two sides of the same quantum coin.

Originally posted by Aim64C

What else could red-shift all those galaxies besides the Doppler effect?

Logically, this does not have to be answered. Experiments would have to verify red shift of light to be a reliable indication of velocity and distance at scale. Obviously - this is very difficult to do with our engineering and technological capabilities. Which is why I find it difficult to respect any individual who claims to be capable of knowing much about the cosmos - much less when they claim to know its origins or ultimate fate.

Huh? Point literally any telescope at any galaxy besides Andromeda and you will verify the redshift.

edit: or do you take issue with the idea that light can be redshifted? This is observed in laboratories on earth on a daily basis.

Originally posted by Aim64C
Then why tout the theory about as if it were fact?

Nobody is touting a theory as fact. These are the models which best fit the data and our understanding of physics, to date.

Originally posted by Aim64C
Where's the evidence for dark matter? Dark energy? ...

Evidence for dark matter can be found in galactic rotation curves, galactic dynamics within galaxy clusters, gravitational lensing of said clusters, microlensing which has recently been observed not even originating near luminous matter, and solutions to the Friedmann equations which result in a flat universe such as ours.

Physicists can't even BEGIN to show you mathematical calculations showing how space would metrically expand (nothing that fits in with experimentally validated models of physics, at least).

See my above post where I do exactly this. Unless you don't consider relativity to be experimentally validated? In which case I'd be happy to run down a quick history of its experimental validation and acceptance.

I am still going with the lava lamp idea: Aren't the Milky Way Galaxy and the Andromeda Galaxy predicted to collide to gether during the next Two Billion years? This was in the internet news a month ago. Doesn't this rule out some of the expansion theory of everything moving apart? Clearly these galaxies are going to smash into one another. One galaxy is obviously moving faster than the other...or the gravity is pulling one galaxy in. I feel we will never know the truth until we talk to extraterrestrials... or leave Earth and travel the universe. Our perspective is too small and how would we ever get proof? Galaxies could be like lava lamp balls that moving erratically around due to energies....

Originally posted by frugal
I am still going with the lava lamp idea: Aren't the Milky Way Galaxy and the Andromeda Galaxy predicted to collide to gether during the next Two Billion years? This was in the internet news a month ago. Doesn't this rule out some of the expansion theory of everything moving apart? Clearly these galaxies are going to smash into one another. One galaxy is obviously moving faster than the other...or the gravity is pulling one galaxy in.

The Andromeda galaxy is close enough that its distance doesn't impart sufficient velocity to escape the milky way's gravitational pull, hence they will collide. Do you think the expansion of space would be the currently accepted model if a rudimentary observation of our closest galactic neighbor could rule it out?

reply to post by Aim64C

Adding more Planck volumes between objects doesn't exactly ring as any more plausible as conservation of energy would create multiple situations in which this volumetric expansion would have to be accompanied by changes of energy states that would trigger release of energy quanta and result in detectable phenomena.

The force of expansion is detectable only on intergalactic distances. In interstellar, and all the way to subatomic distances other forces at play are far stronger than the force of expansion, thus the atoms remain bounded.

There is a hypothesis that, since the expansion is accelerating, over time the force of expansion would become so strong that it would tear even atoms apart, or perhaps the space itself (Big Rip scenario).

reply to post by frugal


Specifically, the Andromeda galaxy is about 780,000 parsecs away and moving toward us at around 140 km/s.
The expansion of the universe causes an apparent motion of 140 km/s away from us at a distance of about 2 megaparsecs.

The expansion of the universe precisely counteracts the proper motion of Andromeda at more than 2.5 times the distance of Andromeda. In other words, the proper motion of Andromeda in our direction is greater than the expansion of the universe at that distance.

The further an object is from us, the more likely it is that the expansion of the universe will cause it to be measured as moving away from us. The fact that Andromeda is one of very few objects so close to us means it is also one of the only objects blueshifted by its proper motion toward us as opposed to being redshifted by its apparent motion away from us.

Originally posted by wirehead

Originally posted by Aim64C
I'm not asking for your condescending, grade-school level answers to this stuff. I'm asking for a real theory - a real model.

Okay. We can write the metric of space as ds^2 = -c^2 dt + a(t)^2 * (dr^2 + S(r)^2 do^2)
where a(t) is a variable scale factor, S is a curve parameterization (0 for flat space, +1 for positive curvature, -1 for negative curvature, depending on your model.)
dt, dr and do are the differentials of time, distance and angular size, respectively, which contribute to the distance measure ds.

From this you can see that the spatial geodesic will scale with a(t). Now, we use Einstein's field equations to find the dynamics of this metric for different arrangements of matter and energy (different stress-energy tensors.) You find that matter will tend to contract the metric, which can either have started with a sufficient "escape velocity" to expand forever, or reach a standstill, or contract, depending.

You can write down equations describing the dynamics of the scale factor accordingly. By solving these equations, you'll then have your description of how space expands or contracts depending on the density and equation of state of the fields which inhabit the space. Then you can play around adding/subtracting matter, radiation, and a cosmological constant, and see how the universe behaves.

Jeeze, he obviously doesn't want your hand-holdy grade school differential calculus answers; clearly he meant he wants to see the full-blown differential geometric calculation, which he can accurately analyze with his advanced degree in math .