How did matter scatter across the universe?

I recently answered a question on quora that has become quite popular.

If the Big Bang took only milliseconds to disperse all the galaxies light years apart, then how did the matter get there faster than the speed of light?

The following is my response.

I love this question - it was the question I had that, when answered well, led to an epiphany in how I understood our universe.

The big bang is described as the creation of the universe, right? Well, it isnt really about the spread of matter across the universe. The big bang is really about the creation of space-time - which happens to have a lot of stuff on/in it. Stuff like atoms.

Lets do a quick thought experiment. Delete the earth from the universe. Then the sun, and the rest of the solar system. Delete the galaxy, and all other galaxies. Go ahead and delete all things in the universe. The universe is now empty. What is the universe now made of? Just the vacuum of space, right? Now what is space? Just some 3d surface on which you can place things - like an atom. We are familiar with the idea of placing things on flat ‘2d surfaces’ - like a book on a table - but when you place something on space - you place it on a 3d surface. Since there is now nothing in space there is no gravity. So if you place a marble in space, it's like placing a marble in a 3d animation program. You can drag it around and place the marble, and then it doesn't move. But what are you placing it on??

You are placing it on space-time.

Space-time is difficult to directly interact with from our perspective. We'd like to be able to grab it, or manipulate it, but we can't seem to. The fact is, we ourselves are simply placed in/on it. But, strangely enough, we know that space-time can actually be stretched and compressed. For some reason, matter that contains the Higgs Boson (the particle/field that gives matter mass) will pull space-time towards it. When you have an enourmous number of these in a very small volume, space-time can be stretched so dramatically in towards them - that it creates what is called a black hole. When space-time is stretched towards some point in this way, you can literally slide down it. Thats what skydivers are actually doing - sliding down space-time that has been stretched by the mass of the earth. This is what is referred to as ‘curvature of space-time’. Einstein - through his theory of special relativity - demonstrated that gravity isn’t due directly to some particle, and its not a force… its actually caused by things sliding down stretched space-time at different angles (i.e. e.g. orbits).

Can you imagine what stretched space-time looks like? Grab a pen and hold it pointing straight up and look at the little ball in the tip. Now imagine the rest of the pen doesn’t exist. If that little ball had a lot of mass, what would space-time do? It would stretch in towards the tip uniformly from all (infinite) directions in towards the center of the ball. And there wouldn’t be a boundary (like a sphere of some size) around the ball. The curvature of space-time induced by the mass would technically be assemptotic to perfect ‘flatness’ (uniformly uncurved space-time) as the distance from the ball increased. This is very strange indeed.

At this point were not entirely sure what space-time is, but there are reasonable yet insufficiently supported theories abound. So, as an analogy - it's like that table you put the book on, or the 3d animation program.

Electromagnetic radiation - light - is a wave that propogates through space-time. It's very different from a mechanical wave - like sound through air - because the mechanical waves are physical atoms pushing against one another down the line. And of course that atom is just a thing positioned in/on space-time. Light doesn't propogate like that, but the wave behavior is similar. Light propogates through the thing that the mechanical waves are positioned on. It propogates through space-time itself. And yet - when light encounters our retinas, we see it! How is it that something (light) that propogates through something we can't seem to interact with (spacetime) can clearly interact with the stuff that is positioned on it (atoms, like in your retina)!?

Since space-time is where everything happens, and we don't really understand space-time - we are left with a lot of mysteries about the universe. Nevertheless, it's pretty clear that light, matter, and space-time all share something deeply fundamental. That's what our theoretical physicist are working on. If we can understand space-time, perhaps we can manipulate it to suit our needs. And perhaps we’ll also understand where it came from, what it's made of, what (if anything) contains it, what its future is, and so on.

Alright, last thing - can spacetime be created/destroyed? Who knows! Can it be added or removed? Well it seems like it can. The universe did seem to inflate, after all, though maybe all of space-time was already present to begin with. And black holes appear to maybe consume it - though perhaps not really (but I like this theory, it's interesting - space-time pouring into a black hole to create another universe inside - like an inflating bubble - which has its own black holes seeding other universes). Ultimately - there are people with different preferences since we still lack a fundamental understanding of space-time in order to fully explain it.

So - when we think about the big bang, we usually think about matter being blasted across the universe - but that's not really the important part.

The big bang is all about the creation of space-time itself. There are no theoretical limits that we are aware of on how fast space-time can expand (or inflate, as it were). The only rules are about how things behave while in/on space-time. Like, for example, the maximum speed that electromagnetic radiation can propogate through it - i.e. light speed. As it happens - a lot of matter was also produced somehow during the bang - that may or may not have been required for the big bang to have occurred - though probably.

When that singularity at the beginning had enough and decided to finally blow (not literally) - space-time expanded/inflated much faster than light could travel across it. It also inflated a lot faster than the matter that was scattered could travel. At the very earliest moments just after space-time began inflating, all the energy of the entire universe - which up until now had been concentrated into / originating from a single point - was suddenly no long constrained, which resulted in what we talk about as the super dense non-hemogenous super hot ball of what had to have been pure energy simply pushing outwards in this newly created ‘space’ in what you may call a ‘big bang’. And there was so much dense energy that - even with inflation - it took about 380 thousand years for there to be enough dispersion of energy (cooling) for the first atoms to precipitate out (remember, E=mc^2… matter with mass IS energy, and therefore that original ball of energy was all the matter with mass from the entire universe in one spot).

So really, there were two things happening: 1. the sudden inflation of space-time, which helped to spread energy apart by increasing the amount of space-time between any two points and 2. The outward accelleration of energy spreading it apart slower than the speed of light

Its generally thought (under this model) that inflation lasted only a quarter of a second or so. At any rate, as more space-time came into the universe - or perhaps as a dense amount of space-time decompressed - the stuff over to the left ends up on the left side of the universe and the stuff on the right ends up on the right basically instantly (not literally).

So you see - to answer your question again - it's not that matter like planets and stars flew away from each other faster than light - we know that is impossible:

The space-time between matter grew at a rate such that the amount of time that has passed since the big bang is less that the amount of time it would have taken for matter to have moved apart to such distances traveling at the speed of light. Therefore - to the naive observer - it looks as if the matter had to have travelled faster than the speed of light to reach such distances. But no - it was space-time itself that inflated, increasing the amount of space-time between the matter - the matter need not have necessarily even moved at all.

For some reason people like to use the balloon analogy to describe the inflation of the universe - where the marble from our thought experiment would be placed on the surface of the balloon and the addition of space-time to the universe is like adding air to the balloon. If you draw dots on the balloon all over and then blow the balloon up a little more (inflation), you see that all the dots move away from each other evenly at the rate of inflation. This may consfuse the issue of ‘where was space-time added to/from?’ and possibly incorrectly beg the question ‘if air is added to inside the balloon, to the inside of what was space-time added?’. Thinking that the univere is in any way the same as a balloon (outside the potentially coincidental analogous spread of the dots due to inflation) may be as erroneous as thinking that the surface of a table is 2D.

If you found this interesting, feel free to confirm what I’ve said from the original publications.

WMAP Inflation Theory

Thanks for reading. Hope you found that enjoyable and illuminating.