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What about it expanding everywhere at once? and we are limited by light speed so we can onky see X amount. So to us we are the centre but that doesn't mean there needs to be a centre

It's not that we can't figure out the center of the universe, it's that there is no center of the universe. The big bang didn't explode out from a single point, it happened everywhere at the same time. It's difficult to picture intuitively, but think of it like an infinite elastic sheet with every point on the sheet one plank length away from every neighboring point (or just think of them as really, really, really, really close together). Then stretch the sheet in all directions so that the distance between the points doubles, then doubles again, then again, etc. Now imagine the sheet as a three-dimensional infinite object (or just infinite sheets one on top of the other starting a plank length apart), and now stretch that stack of infinite sheets in all directions so that the distance between any point and its neighbors doubles, then doubles again, and again, etc. This is kinda sorta what the big bang was. It happened everywhere and distances between points in the universe just kept getting bigger ad bigger and bigger (and they still are). There's no single place where that expansion started (i.e., no center). The expansion happened everywhere.

No, let's take inflating a balloon for an example.you blow air to it and it expands (take that as big bang) now that it expanded it's hollow inside(there's only air in it) now mark 2 points on opposite sides of the balloon. Imagine that our Galaxy is at one point and at the point onopposite side is another Galaxy. We might be looking at that galaxy and then observe that there's lot of empty space in the middle( middle of balloon filled with air). But we don't see anything like that so big bang is fake?

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But the Big Bang didn’t happen in the same way as an inflating balloon. Your premise is false. The expansion happened everywhere. That is, each measurable point in space grew (and continues to grow) further from all other points in space. This is called inflation and expansion.

Edit: I should add that for this reason, every point is the centre of the universe relative to all other points. If you were able to teleport to the edge of our observable universe, you’d be at the centre of a similarly-sized observable universe “bubble.”

But matter can't be created nor destroyed right? How did small atoms expand themselves to become size of galaxies. I thought big bang was like a supernova where a massive amount of matter exploded. But if universe really starched itself like rubber then how does dark matter exist in between galaxies and which external force was applied on universe to stretch it?

Or the balloon is so humongous that we only see a tiny fragment of it that just feels flat, hard to tell with the data we're given

Can you figure out centre of a complete eclipse balloon? Big bang is that tiny fraction of second between zero air in Balloon to perfect eclipse balloon. And it's not done yet. It's still blowing outwards dominated by dark energy. Think of galaxies as polka dots on balloon when their is no air. Now with a air filled balloon those dots are light years apart. It's not a 100% accurate picture as it's missing gravity and why some galaxies are bound to be merged whereas others drift apart. But it's a good imagination to clear your head that there is no center. Air is filled in the balloon everywhere at same time.

> How did small atoms expand themselves to become size of galaxies.

They didn’t. Until roughly 380,000 years after the Big Bang, the entire universe was a thick opaque cloud of plasma of electrons and nuclei.

As the universe expanded, it cooled off enough to let the plasma become atoms, and the cosmos became transparent.

It is space itself that’s expanding, not the particles.

> I thought big bang was like a supernova where a massive amount of matter exploded.

This is a common misconception. A supernova is the explosion of a particular size star that occupies a point in space. The Big Bang was not an explosion, but the expansion of space.

Imagine infinite points packed together with infinite density. Those points occupy everywhere. There is no inside or outside.

Now imagine each of those infinite points moving further from its adjacent points, with the space between them expanding at an increasing rate.

For 380,000 years, the universe was entirely comprised of plasma but then it cooled enough that the electrons and nuclei combined to form atoms, molecules, dust, stars, planets and so on.

We have evidence of the above (post-380k years) since the discovery of the cosmic microwave background radiation (CMB).

>which external force was applied on universe to stretch it?

The best current hypothesis is Dark Energy, but we can only measure its effect. It falls outside the known laws of physics.

Edit: some relevant reading

In your analogy, and I can't stress that it is an analogy enough, the surface of the balloon is representing 3d space. We don't see the interior of the balloon because it's not the universe it's the shape that the universe is curved around.

What we actually observe is that distances on a cosmic scale are all getting longer at a range proportional to their length. This is distinct in some ways from observing objects moving away from us, specifically it isn't restricted by the speed of light as the objects don't really have the velocity that the changing distance to them implies.

Try Google "big expansion" The baloon is a good example, but think of the Atoms of gas inside, and not the surface. each trying to get as far away from each other, while it gets bigger without adding anything. thats why we cant see futher away than 13b lj. It was too dense for light to travel and too hot for Atoms to condense. At least thats how i understand the latest models as Amateur...

E: spelling

I understand quite a lot now thanks. But i still don't get where did the dark matter come from that's expanding the universe even more and accelerates it🤔

The short answer is, we don’t know.

I highly recommend you watch this lecture by Lawrence Krauss, “A Universe From Nothing”

*dark energy not dark matter

> But matter can't be created nor destroyed right?

Sure it can, nuclear reactors turn mass into energy - or is it even matter if the released energy is actually the binding energy of a nucleus which appears as mass?

Energy can't be created or destroyed though (except by the big bang apparently), only transformed from one form to another.

> How did small atoms expand themselves to become size of galaxies.

They didn't start off as atoms, the Universe was far too hot for atoms to form for about 380,000 years - and the CMB is the remains of the light that was flying around at the moment when things were cool enough that atoms could form and the universe became transparent.

If you're wondering why it didn't all collapse into black holes at that density, we think that might be where the black holes at the center of galaxies came from…

Also, the expansion doesn't have a border or edge, it's more useful to imagine new empty space being injected everywhere all at once, like infinite raisin bread rising.

> I thought big bang was like a supernova where a massive amount of matter exploded

Nope, it's a time-like surface from which energy and spacetime poured forth, and could reasonably be described as a white hole - you can draw a ray in literally any direction you like, and it'll eventually intersect the big bang at the moment of our universe's creation.

> which external force was applied on universe to stretch it?

We have no compelling evidence for anything outside our 3+1 perceivable dimensions, and what we can see is same-ish in every direction for as far as we can see, so why not an internal force?

It's called dark energy fwiw, and it's an ongoing field of study since we know almost nothing about it

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