You can’t think of energy density in the same way that you think of density of matter. There was no mass at all in the inflationary universe. You can’t compare that to the density of matter today.
In the same way you can’t ask what forms of energy there were. It’s more than just not containing matter: none of the basic forces of the universe - strong force, weak force, electromagnetism, and gravity, and any other “fifth” forces that we may discover - existed yet either. Without those we don’t have meaningful words to describe “forms” of energy.
The baseball stadium analogy doesn’t work either. That’s just a variation of the old “solar system” analogy and that’s been discredited. The electron isn’t like a gnat in an outfield. It is a probability distribution. What is that? It’s a quantum thing. You wouldn’t understand.
Alright, I’ll take a crack at this. In order to answer this question, to really truly understand where energy and matter come from, you have to understand spacetime, the fabric of the Universe, on a quantum level. (Note: no one has done this yet.)
You see, physicists have figured out that because of the inherent indeterminacy of the Universe on quantum scales (the miniscule volumes in which the interaction between individual particles becomes significant), the so-called “vacuum” actually allows for particles to appear and disappear again. This means that if you have some initial state (an initial arrangement of energy in the form of, let’s say, photons of light) as those photons zip around, the vacuum allows some of that energy to be spontaneously converted into pairs of particles and antiparticles.
Usually a particle and its antiparticle will immediately combine and annihilate into energy again. This gives rise to another great question in cosmology: Why do we see so much matter and so little antimatter? Possible answers to this include: “we simply happen to be in a relatively small, localized region of matter and there’s lots more antimatter way the hell out in space”, and “there’s a teeny tiny asymmetry to the laws of physics and slightly more matter was created than antimatter, and we’re what’s left over after the rest annihilated”.
You’ll notice I left one question completely unanswered: Why was there some initial energy? This is why, as Small Clanger noted, your question is the same as asking “Why is there something rather than nothing?”
Let me know if you figure that one out. I know some guys in Stockholm that would be very interested in your answer.
Although the situation is not exactly the Big Bang, here’s a visual example of matter being created from energy: electron-positron pair production.
A caption: High energy photons coming in from the left convert into electron/positron(=anti-electron) pairs. The electrons and positrons leave visible tracks in the detector (here, a so-called bubble chamble), and a magnetic field bends their trajectories by an amount inversely proportional to their momentum. There are two separate photon conversions in the image, one on the right and one on the left. The extra track in the left one is a scattered atomic electron.
Poof. Matter.
(I don’t want to mislead. The Big Bang is not simply a scaled-up version of this. But, particle production like this is a key component of the answer to the original question in the OP.)
If you want analogies, consider this along with the baseball stadium.
It is theorized that neutrons, protons, electrons, and other wave/particles are made up of smaller bits of energy called Strings. Imagine these as little circles made of fuzzy energy that wiggle up and down like ~~~~~~~ wrapped around on itself and the highs and lows are dipping up and down like a merry-go-round. Then, don’t mention this analogy to anyone who has studied physics or they won’t talk to you anymore.
When you get the scale of the solar system in mind, let me know, because I haven’t done it. Now consider that a String is to the size of an atom what an atom is to the size of the Solar System. When you grasp this an emerge from your coma, you might be able to see how all the matter, which is energy, which might be formed of Strings could be squished into a really… small size.
What you’re describing sounds very much like the surprise at the middle of a black hole. Does such a thing really exist? The world may never know.
I would definitely recommend A Brief History of Time by Stephen Hawking. Easily available at any book store and walks you through all of cosmology in simple(ish) terms.
People always seem to get the understanding of a black hole wrong.
A black hole occurs when enough mass is gathered together in a volume to prevent light from escaping. The size of a black hole depends on the mass of a black hole. A black hole can be any size from microscopic to the diameter of the universe. In fact, if the input the mass of the universe into the equations, you would get a black hole with about the diameter of the universe. The density inside the escape horizon would not be all that great, obviously. It would be almost all empty space.
So the density inside a black hole is not a constant and is not necessarily enormous.
There is a black hole that is assumed to be at the center of our Milky Way galaxy. Estimates are that it contains about 4 million times the mass of the sun, but is at least a billion miles across. That’s a lot of mass, but the density is obviously a tiny, tiny, tiny fraction of what the early universe was.
Sorry to disagree EM, you pretty much always know your stuff, but in this case you’re not correct. There was exactly the same amount of mass in the very early universe as there is today.
Well, it’s nice to hear they actually agree on something.
However, various descriptions of the instant after creation describe the universe as entirely composed of photons. And various description of photons insist that they have no mass. So, for some values of very early, it seemed to me that the universe had no mass, for some definitions of mass.
A system of photons that has (actually “have” sounds better here) a zero momentum frame has mass; which must be the case in the very early universe.
Also the magnitude of the energy-momentum four- vector is not zero, and mass equals this magnitude. Since momentum is conserved these values for mass cannot change as the universe ages.
An interesting fact: If the universe is now infinite it must have been infinite at the big bang.
A system of photons that has a zero momentum frame has mass, which must be the case in the very early universe. Since momentum is conserved these values for mass cannot change as the universe ages.
Also the magnitude of the energy-momentum four-vector is not zero, and mass equals this magnitude.
An interesting fact: If the universe is now infinite it must have been infinite at the big bang.
In trying to oversimplify the complicated, I always hit a point where the experts step in. Yes, obviously mass and energy are equivalent. But I was trying to make the point that physical particles of massed matter, as in the stuff that composes the universe today and in also the stuff that black holes are made of, were not present in the early universe. I used mass rather than matter because otherwise I would get into the nitpick that photons or other basic units could be called matter. I lose either way. Bear in mind that I’m trying to explain this stuff in the simplest possible language. Feel free to correct me when I obscure a technicality this way, but also remember that the audience we’re writing for understands none of the basic concepts.
Any simplifying statement in physics can be nitpicked, and I would normally leave these alone. But your statement that “there is no mass at all…” was more than I could bear. In any case I find you to be one of the more enlightened posters on the SDMB and I always enjoy reading your stuff.
This begs the question; where did the big bang occur? If I was to go outside and look up, in which direction should I point, to indicate where it all started?
The big bang occurred everywhere. There is no privileged center to the universe. It is identical on the largest scales in all directions and from all perspectives.
That means there is no answer to your question. The big bang was not a place, not a center from which things emerged. It affected everything all at once. This is hard to understand, but any good book on the big bang will try to explain it in more words than we can post here.
I am still counting my photons, wondering how many times 0 + 0 is not going to equal zero. Do you just squeeze the pencil real hard, or something?
Not to mention wondering how all these concepts which are defined in the universe now in terms of seconds, and meters are going to turn out when both of those values are 0 too. If E=mc[sup]2[/sup], and c is zero, then well so is everything else. Anything defined with either length, or time in the value is . . . well, undefined, or zero. Doesn’t momentum have a velocity in it somewhere? In fact, I am informed that the momentum of a massless particle is Planck’s constant divided by wavelength, and in this example the wavelength must be zero, so the momentum has to be undefined, not zero.
One entire Planck interval later, I will believe pretty much however much matter or energy you want, but the actual instant of the singularity strikes me as . . . well, zero. I could live with undefined, however, as it seems appropriate. However, it seems to me that zero is a fairly small value of early. And the sum of an infinite number of zeros looks like a pretty small mass.
I am not a physicist. But, I don’t think it’s as sewn up as it is being presented.
Also, whatever it is that causes the Heisenberg Uncertainty ain’t operating yet, either, because everything is moving at the same velocity, namely zero, and has precisely the same location, namely right here. It seems to be an inherently unstable situation, and I expect it will all fall apart shortly. But that’s later, this is now.
