Big Bang - Where's the hole?

Originally posted by Moduli
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

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I would have loved to have derived the Friedmann metric from assumptions of isotropy and homogeneity, but I'm afraid I'm not yet familiar enough with general relativity!

Originally posted by wirehead

Originally posted by Moduli
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

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I would have loved to have derived the Friedmann metric from assumptions of isotropy and homogeneity, but I'm afraid I'm not yet familiar enough with general relativity!

Pick up a copy of MTW from Amazon then . It's rambly and long-winded, but good! And not as difficult as people say.

Originally posted by Moduli

Pick up a copy of MTW from Amazon then

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Lord of the Rings for GR over-enthusiasts...and a book I wish I had a copy of (though my random assorted PDFs on GR and Tensor Calculus have sufficed so far).

Originally posted by wirehead

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.

Poppycock. Its only validated and accepted by people who want GR to reign indefinately
regardless.
Anyway you will keep going in circles over this

Originally posted by Angelic Resurrection

Originally posted by wirehead

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.

Poppycock. Its only validated and accepted by people who want GR to reign indefinately
regardless.
Anyway you will keep going in circles over this

And, you know, experiments. And field theory. And solid state physics, like the kind used to make your LCD screen, or hard drives, or ipad, or hundreds of other solid state devices. Oh, and all of electromagnetism, that's all relativistic, too. It's trivial to show that electromagnetism is contained in relativity.

Right, but I'm sure your radio was built by people in on the huge relativity conspiracy and are keeping the way it really works secretly hidden to you .

Originally posted by Moduli
And, you know, experiments. And field theory. And solid state physics, like the kind used to make your LCD screen, or hard drives, or ipad, or hundreds of other solid state devices. Oh, and all of electromagnetism, that's all relativistic, too. It's trivial to show that electromagnetism is contained in relativity.

... and astronomical observations of classically occluded stars during an eclipse, decay of orbits due to gravitational waves, gravitational lensing, gravitational redshift, the recent observation of frame-dragging due to earth's rotation, time dilation of half-lives of cosmic ray particles, even the construction and operation of GPS satellites, and literally every replicable test of relativity conducted to date.

Or, you know, maybe one guy's unlettered opinion that it's all poppycock is sufficient to overturn decades of research, observation, experimentation and theory.

Originally posted by wirehead

... and astronomical observations of classically occluded stars during an eclipse, decay of orbits due to gravitational waves, gravitational lensing, gravitational redshift, the recent observation of frame-dragging due to earth's rotation, time dilation of half-lives of cosmic ray particles, even the construction and operation of GPS satellites, and literally every replicable test of relativity conducted to date.

And of course, all the results interpreted to suit the GR hype

reply to post by wirehead

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.

You act like you're telling me something I don't know.

The problem is that this doesn't actually work to explain volumetric expansion of space. Applying special relativity, I can argue that a ball thrown into the air is experiencing the effects of volumetric expansion brought about by a dark energy as opposed to a physical force.

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.

This is what is known as the FAPPTRAP.

I think there was an innuendo in that expression when it was created... but perhaps that's just modern influences reading into it.

Basically - "shut up and calculate."

Doesn't really do much to explain how space expands - since you've not really defined space as anything other than the arbitrarily established units spanning two objects.

I would advise against regurgitating a text book toward me. It is a useless endeavor, as A) I already know and B) I'm proposing logical flaws in the concept - which are not going to be resolved by throwing more arbitrary equations at the problem.

reply to post by CLPrime

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.

Thank you.

Of course - this isn't volumetric expansion of space - this is spontaneous emission of energy from the zero point that can, at least in theory, react kinetically.

That's different than a physical alteration of space. Though when your only agreed upon concept of space is the distance between two points - there's obviously going to be debate over whether or not this constitutes an expansion of physical space or merely implied space.

reply to post by wirehead

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

I can see my statements are going straight over your head.

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.

Stop. Go back. Re-read my posts.

You're utilizing adjunctive reasoning. Example: When a camera flash goes off, a bright light reflects off the wall. A bright light is seen on the wall - a camera flash must have gone off.

In this case: Movement results in spectral shifts of objects into longer and shorter wavelengths respective of receding or approaching emitters. Red shift is observed, therefor said objects are moving away.

If you can't see the obvious logical fallacy involved, then you're not deserving of whatever intellectual certifications you may have.

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

You've really not spent much time reading this thread, have you?

reply to post by wirehead

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.

You don't really understand what evidence is.

The "evidence for dark matter" is really evidence for an incomplete model of gravitation.

Dark matter is one proposed amendment to the model - which has no evidence of its own existence (in fact - the model has had to be continually tweaked as predictions of dark matter distribution have been wildly off the mark when compared to results of studies to identify mass distribution in galaxies).

There are other theories with equal amounts of supporting evidence (not a huge qualifying mark) - many of which resolve the issue without the involvement of gravity gremlins.

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 addressed this in my previous post - but I'll recap:

Einstein's field equations do not define space as anything other than a metric derived from the propagation of light. It is treated as a derived (yet arbitrary) metric.

Basically - I asked you how a transistor works, and you referred me to Ohm's law so that I could calculate the thermal dissipation its load. Transistors require a quantum mechanical explanation (if you want to be proper) that cannot be mechanically explained without quantum phenomena (though they can be functionally illustrated).

Originally posted by Aim64C

There are other theories with equal amounts of supporting evidence (not a huge qualifying mark) - many of which resolve the issue without the involvement of gravity gremlins.

Modified gravity theories fail dramatically in reproducing the observed density fluctuations of the early universe.
edit: and of course, the observed gravitational lensing of, e.g. the bullet cluster merger.

Einstein's field equations do not define space as anything other than a metric derived from the propagation of light. It is treated as a derived (yet arbitrary) metric.

What exactly is the problem? Einstein's equations describe how space behaves based on its mass-energy content. This is why a negative energy density (as in a cosmological constant or a negative vacuum expectation value) leads to expansion, whereas normal matter / radiation (having positive energy density) lead to contraction.

You seem to take issue with GR for some reason. Perhaps you could just explicitly lay this out for us.

The problem is that this doesn't actually work to explain volumetric expansion of space. Applying special relativity, I can argue that a ball thrown into the air is experiencing the effects of volumetric expansion brought about by a dark energy as opposed to a physical force.

No, you couldn't really argue that. Dark energy enters the dynamical equations in a different way, and describes a different phenomena. E.g. if that were the effect of dark energy, you'd expect to see its effects on everything else in the universe, not just the ball.

In other words, it wouldn't fit the data.

Originally posted by Aim64C
Doesn't really do much to explain how space expands - since you've not really defined space as anything other than the arbitrarily established units spanning two objects.

Which is all we need to take space to be, to derive the results of GR.

Originally posted by Aim64C

In this case: Movement results in spectral shifts of objects into longer and shorter wavelengths respective of receding or approaching emitters. Red shift is observed, therefor said objects are moving away.

Obviously other possible explanations for redshift have been proposed (such as the tired light hypothesis) but they do not fit the data.

So, without further prevarication, perhaps you would like to explain your interpretation of the redshifts we observe?

Of course - this isn't volumetric expansion of space - this is spontaneous emission of energy from the zero point that can, at least in theory, react kinetically.

That's different than a physical alteration of space. Though when your only agreed upon concept of space is the distance between two points - there's obviously going to be debate over whether or not this constitutes an expansion of physical space or merely implied space.

First, it isn't "spontaneous emission of energy." That would be present as quanta of the fields propagating. It's simply an energy content in a volume of space- it is the zero point energy. If this zero point energy is negative, when it enters the stress-energy tensor it will tend to accelerate the expansion of space.

Second, the cosmological constant doesn't need to be related to quantum mechanics at the moment, this is just one possible interpretation of it. It enters the theory in a manner analogous to a constant of integration- it's a mathematical possibility. Interpretation is another thing.


But this is all beating around the bush. Please, regale us with your concept of space.

Originally posted by ImaFungi

yupp thats my biggest problem,..,,.,.. if its not made of anything,,, it does not exist,,,,,

Of course it exists! It's space! You're in it right now!

the surface of the earth can be curved because it is a 3d object,,, a shape,.,.,.. space is not an object or shape,.,.,.,

Ah, but it is a shape. "Shape," "curve," etc. are all generic properties of any space.

reply to post by wirehead


"What is space?" has got to be one of the hardest questions to answer. We can answer mathematically (it's a pseudo-Riemannian manifold, a metric/tensor field)...we can answer indirectly (it's the volume in which all mass/energy is contained)...but we can't get much better than that. It's hard to describe something that is undetectable, unmeasurable, and beyond our perception.

So, yay for math, that it at least lets us model the geometry of space without needing all those pesky details.

"Of course it exists! It's space! You're in it right now!"



ok,,, so lets say space is infinite,,,, beyond the current scope of the physical universe space "exists" in infinite directions in all directions for infinity,,..,,..,..,,. the space between the items of the physical universe is arbitrary and only results from the physical properties, laws and forces of these physical bodies,, and how they react with each other..,.its the same "kind" of space that exists infinitely beyond the universe,,, its just that matter happens to be present in this area,,.,.,. this is what i mean when i say space does not exist,,., or do you think that space,,, the space between the matter of the physical universe is unique in and of itself compared to space that may be surrounding the universe,,,,, and if so,,, would it only be unique because the properties it shows when we observe matter interacting at distances make it seem like there is more to the empty distance between celestial objects then; the absence of objects .,, ,,.

there for in my mind the universe can be looked at how a fish swims or caterpillar moves,., using its own self to slingshot,, or catapult, or leap frog it self to grow and move at all,,,.,.,. obviously in a much more extreme circumstance.,,.,.,.,. another analogy may be a seed that grows only using what it contains within its original structure,.,.,.




also i understand that space must exist,,,,, the distance between objects is real and true,,,,, but when i say space does not exist,,, im trying to understand if that distance is composed of anything,,,,, or is it thought like i think the big bang insinuates that the separating of matter is what draws this space/distance into "existence" for it is necessary for the matter to exist in the way matter exists and in turn the "nothingness" of space gains existence...

reply to post by Maslo


Sorry Maslo, I have been away for a while, and did not see your question.

I am not saying there is a central point on the outside of the baloon, where all the galaxies are moving away from each other. All I am saying is there is a central point inside the baloon, from which everything is moving away from 360 degrees.

If we are taught that all matter started at a single point, being a spot smaller than an atom, which is what we are taught, and which I disagree with, or an area the size of a galaxy, which I find more believable, then there has to be a spot where everything is moving away from 360 degrees.

Now that spot, where everything began moving away from each other, could be different now, or maybe does not exsist anymore, due to variations in gravity, and other things that we may not know about.

It is nice to know, that there are many intelligent people here at ATS, where someone like me, not trained in science,can come and ask questions. We can disagree, but at least we can be civil about it.

One of the many reasons I have visited ATS almost daily, for the last 5 years.

Thanks again to all. And no matter how the universe started, or how it will end, I wish all of you the best. Peace

Originally posted by ImaFungi
ok,,, so lets say space is infinite,,,, beyond the current scope of the physical universe space "exists" in infinite directions in all directions for infinity,,..,,..,..,,.

Yes, this is a possibility.

the space between the items of the physical universe is arbitrary and only results from the physical properties, laws and forces of these physical bodies,, and how they react with each other..,.its the same "kind" of space that exists infinitely beyond the universe,,, its just that matter happens to be present in this area,,.,.,.

Well, the space between e.g. galaxies is determined by the behavior and nature of those galaxies, yes. This is because there is a deep relationship between space and matter. The matter content determines the nature of the space, and the space determines (partially) the movement of the matter.

You seem to be postulating a finite region of matter surrounded by infinite, empty space. I'm not quite an expert (maybe other people want to chime in here), but I do know that Einstein rejected this model on the basis of Mach's principle.

this is what i mean when i say space does not exist,,., or do you think that space,,, the space between the matter of the physical universe is unique in and of itself compared to space that may be surrounding the universe,,,,, and if so,,, would it only be unique because the properties it shows when we observe matter interacting at distances make it seem like there is more to the empty distance between celestial objects then; the absence of objects .,, ,,.

The thing is, you can take general relativity and ask "what does this theory say should happen if we arrange matter in this specific way?" and get a concrete prediction. Then, you go looking in the heavens for that specific scenario and you find exactly what the theory predicted.

It is possible that somehow the effects you're seeing are not due to the curvature of space by matter, but when general relativity starts to pass test after test (and there have been many!) over the last century or so, you can be confident that as a model it fits the data and is therefore useful. It happens to describe things in terms of curved space; this is likely what is occurring.

Things like gravitational lensing, for instance, can't be explained in the context of euclidean (what you would call "simply empty distance") space.

Originally posted by zeta55

I am not saying there is a central point on the outside of the baloon, where all the galaxies are moving away from each other. All I am saying is there is a central point inside the baloon, from which everything is moving away from 360 degrees.

In the balloon analogy, this central point is precisely the big bang. Remember that the balloon is a 3D object with a 2D surface, but in relativity we model the universe as a 4D object with a 3D surface + 1 time dimension.

So, the central point in the 3D balloon corresponds to a central point in 4D space, which means it has to be located not just in 3D space but in space and time. Therefore, it's not just a place but an event. The central point from which everything is expanding is located back in time.

Originally posted by ImaFungi
also i understand that space must exist,,,,, the distance between objects is real and true,,,,, but when i say space does not exist,,, im trying to understand if that distance is composed of anything,,,,, or is it thought like i think the big bang insinuates that the separating of matter is what draws this space/distance into "existence" for it is necessary for the matter to exist in the way matter exists and in turn the "nothingness" of space gains existence...

edit on 8-7-2012 by ImaFungi because: (no reason given)

Like CLPrime said, it's really difficult to answer the question "what is space?" or "what is space made of?"

I would, however, submit that if it is in some sense "made of something" then we can't really describe that thing in terms of physical stuff. As you pointed out, space isn't a physical thing.

So, I could say "space is like a collection of rubber bands," but that would be cheating you in some sense. Because we know rubber bands are physical things which occupy space, they're made of stuff, and space isn't, in that sense.

The best we can do is use science and experiment to try to determine how space behaves; maybe someday we'll be able to explain what it is in some sense. But, we can already say from our current understanding that space is allowed to bend, and this is related to its matter/energy content by Einstein's field equations.

Ok...let's PRETEND...a bang did actually occur. How did EVERYTHING fall PERFECTLY into place? How is it that Earth has it's own features, and Saturn has it's own. What keeps EVERYTHING floating in space? Also, how do you explain where LIFE came from??? Why is there life on this planet...and nothing on the rest of them?

Too many questions...not enough answers!

Originally posted by wirehead




So, the central point in the 3D balloon corresponds to a central point in 4D space, which means it has to be located not just in 3D space but in space and time. Therefore, it's not just a place but an event. The central point from which everything is expanding is located back in time.

and this is the basis in the question of the OP..,,.,.., you seem to think of time and the universe as traveling one way all together.,.,., as in the central starting point is back in the arrow of time,.,..,,.. but if the universe had a starting point,.,.,,. and matter and energy spread outward in all directions,,,,, this is what i was curious about as well,,,,, wouldnt that starting point have expanded,,,, as the energy and matter would be traveling in all directions,.,.,.,not just one direction away from a starting point,,.,.,. but all directions surrounding a starting point,,,, meaning if we are over here,,,,,, the direction the galaxies near us are expanding outwardly are expanding in the exact opposite direction outwardly on the other side of that starting point.,


leaving a chasm in the exact middle of the universe.