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Rolci

A question for experts on the Big Bang theory

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I have read many books on the Big Bang myself, all the way back from "The First Three Minutes" and many more since, and also have done a ton of readings into Black Hole physics, but there is a question I have never asked myself. Now the answer is either too obvious and I'm just having a mental block or it might be a serious one, but I just can't reconcile it in myself right now so I'm asking for a quick explanation from someone. Actually I have two now, I just thought of another one. This last one is, at the moment of the Big Bang you have a singularity with zero dimension, right, a black hole with the weight of the entire Universe in it. Now why would it explode in the first place? Why start expanding? Second, and most importantly, how does it keep expanding? Continuously. To my mind right now it would seem that the escape velocity on the edge of the Universe would be like, a zillion times the speed of light. How would all that mass, moving away from the point where the singularity had just been a second ago, how does all that mass, moving almost at the speed of light (meaning it all has even more mass), keep moving, instead of falling back in on itself? Even if you could give a reason for the initial expansion, the amount of gravity is so mind-bogglingly awesome in the first few seconds, and even years, what could possibly counteract it?

I invite anyone to work out the density of the Universe after 10 seconds, or 10 minutes. When does it actually reach the density of a neutron star? OK I worked it out quick. Turns out, if you disregard inflation models (which ends even before you hit the 10-33s mark and which I'm not even sure how it would affect mass, with all that energy soup moving faster than light, and how fast exactly? Anyone got formulas?) density drops down to the level of neutron stars (50.000 tonnes per square millimeter) after a whole hour of expansion! WTF?? So after 1 hour you still have a neutron star 1000 times the size of a sphere that has the Earth's distance from the Sun as its radius! And this neutron star is expanding. Yeah, it's not, I've got it. But what does that mean hear and what exactly is making it so different from a neutron star? What makes it hot that doesn't make a neutron star hot, and is it the heat that makes it expand in spite of all that gravity or is it something else? And how can heat be enough? Simple pressure counteracting colossal amounts of gravity or what? After an hour the temperature is about the same as in the centre of the Sun, but definitely less than 100 times that. If that temperature is not enough to inflate stars with their low density, how can that same temperature inflate a neutron star? (Actually there were already protons and neutrons, although I'm not sure why those protons didn't form neutrons when hit be electrons. They should've done and we should have plenty of positrons today.) OK I won't even go further than this right now, I want an answer! I admit it's been a while since I last read The First Three Minutes or anything similar, I've been more into black holes recently. So somebody, please enlighten me. Thanks!

Edit: I have found http://math.ucr.edu/...s/universe.html and http://www.nature.co...niverse-1.13743 but it's 3:40am and my brain is dead! :D

Edited by Rolci
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Don't assume the universe started in singularity. It's not that the mass of the entire universe was all there and exploded. Energy and mass are interchangeable so all that is needed is energy. I have heard that it has been estimated that a 10 kg mass heated to a trillion trillion degrees would inflate to the size of the universe we see today. I am no expert in this but try this video it may give you some answers.

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I think the biggest problem with what the OP says is that the Big Bang was an explosion.

It had and still has the property of all its constituents moving away from each other in a symmetrical (probably) way, which is common of explosions, but other than that it is not comparable to an explosion. Space itself is expanding, and the particles and what-not in it are carried with the expansion, so that if you didn't see the rest of the universe you would not perceive yourself as moving.

Also, it seems (someone please explain this to me if I've got it wrong) that the energy (of which some later became mass) did not exist at the "very" beginning, but was almost entirely brought into existence as part of the processes involved in inflation. This is what leads me to think that the reality is there is no limit to energy if one can tap it -- shades of Achilles and the Tortoise if existence and the energy buried in it is not quantized (even though our particular space/time may be).

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Some think the forces were unified early on and did not separate till latter. This would include gravity. But the "big bag" is actually a horrible name that gives a lot of bad conceptual cues. This guy does a great job with his physics. I liked it so much I copied it a bit.

http://youtu.be/q3MWRvLndzs

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Some think the forces were unified early on and did not separate till latter. This would include gravity. But the "big bag" is actually a horrible name that gives a lot of bad conceptual cues. This guy does a great job with his physics. I liked it so much I copied it a bit.

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Yeah Big Bang is actually a name given to it by proponents of the steady state theory trying to discredit it. Hyper inflation is actually better I think.

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"Big Bang" is the name we now have, and although Howell used the expression in ridicule, Gamow and others were not so uptight as to not see the ribbing and accept it. It's nice and to the point, so long as we remember it was not an explosion.

What is really misleading is when people try to show it on TV and they show an explosion and even add sound effects. They should try to show some sort of grid expanding and carrying its contents with it.

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"Big Bang" is the name we now have, and although Howell used the expression in ridicule, Gamow and others were not so uptight as to not see the ribbing and accept it. It's nice and to the point, so long as we remember it was not an explosion.

What is really misleading is when people try to show it on TV and they show an explosion and even add sound effects. They should try to show some sort of grid expanding and carrying its contents with it.

Yeah at this point it's kind of iconic. I know there are many theories as to what got it going, like in brane theory when they talk about two membranes basically slapping together and the expansion we see today is them rebounding back apart but I like the quantum fluctuation idea though I still have many questions about it. It seems the initial energy of expansion must have been almost unimaginable

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Yeah at this point it's kind of iconic. I know there are many theories as to what got it going, like in brane theory when they talk about two membranes basically slapping together and the expansion we see today is them rebounding back apart but I like the quantum fluctuation idea though I still have many questions about it. It seems the initial energy of expansion must have been almost unimaginable

Indeed, but a non zero chance in infinity will come around eventually. A virtual particle can tunnel away from its anti twin and not annihilate. Therefore makeing wherever it tunneled to slightly more energy dense. Once in a bagillion years it just so happens on colossal scales. Just like once in a lot of less bagillion years you might tunnel away and pop up in my living room. We simply live in the part of a very large vacuum that happens to be extremely energy dense. The physics of nothing (which really is something) demands that we exist somewhere, and somewhere happens to be hear.

I for one am moved greatly by the idea that the laws of physics demand us to exist.

Edited by White Crane Feather
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I'm not sure; for tunneling and virtual particles and all that you need space/time. If there is no space/time some other mechanism for starting it all is needed -- either that of just say it happened for no cause other than that it happened.

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I'm not sure; for tunneling and virtual particles and all that you need space/time. If there is no space/time some other mechanism for starting it all is needed -- either that of just say it happened for no cause other than that it happened.

agreed. but there is no evidence that spacetime started at the big bang. There is "space" and vacuum. At these points we have to be finite in our definitions and its where a lot of confusion arises. The space between things we know started at the BB, but this simply is not the vacuum which is a better definition of space. If you watch both videos on this thread. Non of the physicists propose that vacuum energy is not a very large player in origins. Its like the use of the BB. The use of the term "nothing" is misleading. as far as we know there is energy everywhere, and its only the manifested density that seems to have a beginning, and even that is in question. Contracting space only means contracting space. Like the speed of light space itself probably is not confined to the laws of the plank.

Edit: I put gravity where I meant the speed of light.

Edited by White Crane Feather

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I am with the OP. I can't see how a singularity can start expanding when it is infinitely dense, and if it did, why a contraction did not occur. This belief in the "big bang" is wide spread throughout society, and the starting point being a singularity. Is this actually explained within the theory? Or is it pure speculation like "the energy wasn't always there"?

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I am with the OP. I can't see how a singularity can start expanding when it is infinitely dense, and if it did, why a contraction did not occur. This belief in the "big bang" is wide spread throughout society, and the starting point being a singularity. Is this actually explained within the theory? Or is it pure speculation like "the energy wasn't always there"?

The evidence of the reality of the Big Bang is really considerable and impressive and convincing for people who have any astronomical knowledge. Whether it is the beginning of existence is not known and I agree with White Crane Feather probably not, but we don't know. The singularity comes from projecting backward and makes a convenient starting point for the mathematical description. More likely it started at something more Plank size and when the phase transition happened that was "inflation" was when the high temperature and density developed, with the expansion going on from there from momentum.
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The evidence of the reality of the Big Bang is really considerable and impressive and convincing for people who have any astronomical knowledge. Whether it is the beginning of existence is not known and I agree with White Crane Feather probably not, but we don't know. The singularity comes from projecting backward and makes a convenient starting point for the mathematical description. More likely it started at something more Plank size and when the phase transition happened that was "inflation" was when the high temperature and density developed, with the expansion going on from there from momentum.

I liked what you said. But if you pay attention to the physics... Momentum had nothing to do with it. :) We are not talking about things through space....we are talking about space itself.

its more like a pressure front in a weather system.

Edited by White Crane Feather
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Yea I know particles in space's expansion don't "know" the momentum of the expansion, but as I understand it space does.

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Yea I know particles in space's expansion don't "know" the momentum of the expansion, but as I understand it space does.

What constitutes "momentum" is really a pressure difference. ;)

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I'm not sure; for tunneling and virtual particles and all that you need space/time. If there is no space/time some other mechanism for starting it all is needed -- either that of just say it happened for no cause other than that it happened.

I'm not sure that follows. What we see as the universe today could be new space which has expanded from a point in already existing space, I think. I'm not sure if I am explaining this well to get my point across but maybe you see what I mean..I also heard of an idea that the big bang happened when a 4th dimensional black hole collapsed and caused a kind of white hole here. Waspie posted a thread on this a while back. I have also heard of an idea that every black hole could wormhole through space time and end in a big bang event in another region of space-time. I have no idea which if any of these ideas might be more plausible though like I said the q-fluctuation one appeals to me. I am still amazed when I think how much our understanding of the early universe has grown in my lifetime. When I was young there were still those who argued for the steady state theory though the big bang had come into general acceptance Edited by spacecowboy342

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I'm not sure that follows. What we see as the universe today could be new space which has expanded from a point in already existing space, I think. I'm not sure if I am explaining this well to get my point across but maybe you see what I mean..I also heard of an idea that the big bang happened when a 4th dimensional black hole collapsed and caused a kind of white hole here. Waspie posted a thread on this a while back. I have also heard of an idea that every black hole could wormhole through space time and end in a big bang event in another region of space-time. I have no idea which if any of these ideas might be more plausible though like I said the q-fluctuation one appeals to me. I am still amazed when I think how much our understanding of the early universe has grown in my lifetime. When I was young there were still those who argued for the steady state theory though the big bang had come into general acceptance

There are a lot of ideas.., which is great, but simplicity is always preferred. We know that that quantum fluctuations exist, we know tunneling exists. It's as easy as 1+1 to me. The bb was a quantum tunneling event of an extremely rare quantum fluctuation in a flat vacuum. It seems so simple to me based on what we know and observe. I'm not even Sure why it is even debated. The COBR is a product of this and expands because its the nature if vacuum energy to expand space. :(

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The precise way the cosmic background radiation fits what is predicted for it is pretty impressive. That new space is being created or that space is expanding seem to me to be two ways of saying the same thing, dependent on two very subtle differences in the way one defines "space."

The idea that black holes generate new space-times in their own set of dimensions has been worked on with some rigor, and seems to hold up. I really can't say much more about it than that I read a book on the subject maybe a dozen years ago, but have heard little since.

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What constitutes "momentum" is really a pressure difference. ;)

Well it was expanding and didn't want to stop. That it slowed down so much is still problematic -- probably another phase transition I guess.
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Well it was expanding and didn't want to stop. That it slowed down so much is still problematic -- probably another phase transition I guess.

Yeah but I have heard speculation that hyper inflation could still be happening in different regions of space time. I love the idea that the total energy of the universe is 0 as this would seem to make sense to me if the universe just came about from a fluctuation out of nothing. I have also heard of theory that the end of the universe might come by another quantum fluctuation which could send a wave of nothingness spreading throughout the universe at the speed of light. Our first clue of this happening would be when we ceased to exist. Probably won't happen for at least 20 billion years according to the program I saw
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Of course: the universe is just one humongous gargantuan free lunch. It appears that all conserved quantities (mass/energy, electric charge, momentum and angular momentum all total zero).

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What constitutes "momentum" is really a pressure difference. ;)

Yeah I think it's important to remember that dark energy is the dominant thing in the universe. All the galaxies and stars we see are just a bit of fluff in a universe dominated by dark energy and dark matter. It's almost like we were a side effect of creation rather than what was created. A bit humbling
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I am with the OP. I can't see how a singularity can start expanding when it is infinitely dense, and if it did, why a contraction did not occur. This belief in the "big bang" is wide spread throughout society, and the starting point being a singularity. Is this actually explained within the theory? Or is it pure speculation like "the energy wasn't always there"?

There are many theories on this but I think it is important to remember that singularity isn't necessary just tremendous energy. There are theories that include singularity that include the idea that somehow under certain conditions gravity could be repulsive. It's been a while since I read about this so I don't remember the details well but still the quantum fluctuation idea makes more sense to me
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Emphasis on the replication of the microcosm ad infinitum -- the fundamental center IS the vacuum itself.

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All of these elements that don't really exist intersect to form our concrete reality.

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