demanbmore t1_j8vz2tx wrote on February 17, 2023 at 9:55 AM

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.

Negative-Fan8460 OP t1_j8vzr1w wrote on February 17, 2023 at 10:04 AM

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?

dulce_3t_decorum_3st t1_j8w0tq4 wrote on February 17, 2023 at 10:19 AM

> 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

triffid_hunter t1_j8w2kp5 wrote on February 17, 2023 at 10:43 AM

> 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