Hard to wrap my mind around this one. Anyone have any good analogies that fit?
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Think of the universe like a balloon. When empty, the universe is small, but nothing outside of it is the universe. Only the balloon exists.
Then you blow it up to simulate the expansion of the universe post big bang. The balloon is bigger now. The amount of rubber in the balloon hasn’t changed, but it takes up for more space.
This isn’t a perfect analogy, but this can be difficult to grasp right away without a mathematical context to explain it in, and is sometimes easier to come back to over time to grasp
You can’t say that there is (or isn’t) a center or an edge to the universe and you can’t say that the Big Bang started (or didn’t start) from a singularity.
Because you can’t say anything definitive about the geometry or bounds of the universe you often see it being described as the Big Bang “happening everywhere”
The Big Bang Theory concerns the expansion of the universe. In this sense, it obviously makes no sense to ask “where did it happen”, because it literally was happening everywhere.
The confusion comes when you start discussing the Big Bang **singularity**. The introduction of this concept starts causing people to think that there’s a single point in space from which all space was birthed and they make outrageous claims like “the Big Bang is the result of a white hole” which from our previous statements is fancifully incorrect. The singularity results from rewinding the clock all the way to t=0 that the totality of space is now infinitely dense. The important word here is **totality** of space. Again, not a singular point. Everywhere. It’s a description of the universe in that “point of cosmological time”.
It’s very important to understand that the Big Bang singularity is **not a component of the existing standard model**. In fact the singularity is itself not even existing in spacetime. There’s a reason you’re talking about it, though. It’s popular. People think of it as the “when time started” because of the way the mathematics works out, but it’s non-mathematical thinking. Time doesn’t need to “start”, it’s purely an index, a coordinate for ordering things. Same thing with the singularity purely capturing a mathematical statement on limits. All inflationary models currently don’t make any statement on what happens before the “Planck Time” so anyone attempting to do so is purely doing a thought experiment. If they attempt to pass it as what the real physical model tells us, then they are admitting ignorance.
Yeah it never said that it was “small” nor “a singular point’, but more like “infinitely dense.”
So you know the universe is expanding right? It’s not that the universe is shaped like a bubble and there’s a wall (the “edge” of the universe”) and that the wall keeps going outward, it’s not like that at all. But it’s more like the space itself is expanding, the distance between point A and point B grows from 1 meter to 2 meter (I’m exaggerating of course). This expansion is so weak that if you have an atom at point A and point B, the gravity etc between 2 atoms can easily overcome the expansion. But over billions of years it adds up.
Now rewind the video. If we play the video backwards, then the universe is contracting. Then you get to the point where everything is closer to each other and it’s denser. At that point atoms cease to exist, it’s replaced by quarks, and what not. Everything is more dense, matter and energy, and infinitely so. We don’t know if it’s just one point or if the universe is already large at that point, we only know that it’s infinitely dense back then. Everything that we can see today (the “observable” universe) originated from a single point. So whether the universe really was not a single point but already large at the Big Bang is kinda a moot point beacuse everything that we can ever interact with (the observable universe) originated from one single point.
Think of a room filled with flammable gasses. Now imagine the gas molecules are rubbing against eachother until they create enough friction to ignite. This happens in many different places at once within the gas cloud.
Now, if you’ve ever seen a slow-motion video of an explosion occuring, you’ll know that a vacuum is created at first. So everything is pulled toward each of the ignition points before exploding outwards.
It always makes more sense to me that whatever it is that we call the big bang happened in absolute nothingness. Which is what ‘space’ would be without the big bang. Anyways very neat and interesting stuff.
The balloon analogy requires scaling everything back by one dimension.
Imagine the surface of a balloon is a 2-D universe. Nothing exists except what’s on the surface. The curvature of the surface isn’t obvious but some scientists theorize that it’s somehow ‘curved’. It has no edges or boundaries, but someone on this 2D universe discovers that every point on the surface is getting further apart from every other point. A theory is formulated that the entire balloon surface was once much smaller and started at one point, and it’s been expanding ever since. Which spot on the balloon was at this creation point? All of them. It’s been expanding through an unknown and unfathomable extra dimension that nobody on the surface can even conceive of.
Essentially the big bang created reality. Nothing existed before, not even empty space. Literally reality didn’t exist.
I think it’s impossible for us to comprehend.
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Imagine you’re a microscopic organism living on a bubble that got formed from someone blowing through a bubble wand. Your universe is the bubble. The bubble didn’t start at a single point (from your frame of reference), it just got bigger as it expanded. From a human’s perspective, you can point to where the bubble is and where it started, but to something whose entire existence is within the bubble, the Big Blow didn’t happen at any single point, but it happened everywhere on the bubble at once.
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