Have we found the Milky Way’s twin?

[Standing Wolf]

There are exceptions to the rule that all galaxies are moving away from all other galaxies. But the exceptions are few.

Gravity is the culprit that attracts matter to itself (imprecise but good enough). Gravity is attractive. Something (anti-gravity) is repelling the galaxies away from one another at very high rates of speed. Personally, I think dark energy is the mechanism.

Dark matter is matter we cannot see but it curves space-time. Dark energy does not. Between dark matter and dark energy they comprise about 95% of everything in the Universe.

But we can only see so far. All of the galaxies that we can see are moving away from us. Physicists speak about space itself as one of the things that emerged from the Big Bang, but who can say what is going on in that part of the Universe beyond our view, perhaps even "outside" the Universe we know (or think we do)?

[Peter1469]

How was the universe created?

Short answer: We don't really know how the universe was created, though most astrophysicists believe it started with the Big Bang.

We know that we live in an expanding universe. That means the entire universe is getting bigger with every passing day. It also means that in the past our universe was smaller than it is today. Rewind that tape far enough, and the physics suggests our universe was once an infinitely tiny, infinitely dense point — a singularity.
Most physicists think this point expanded out in the Big Bang, but because all known physics breaks down in the extreme conditions that prevailed in our universe's infancy, it's hard to say with confidence what happened in those earliest moments of the universe.
Going back in time

For most of the history of the universe, it was dotted with similar celestial objects as are present now — they were just closer together.


For example, when our universe was less than 380,000 years old, the volume of the universe was about a million times smaller than it is today, and it had an average temperature of around 10,000 kelvins. It was so hot and dense that it was a plasma, a state of matter where atoms are ripped apart into protons, neutrons and electrons. However, we encounter plasmas in many other situations in space and on Earth, so we have a pretty good understanding of how they work.


But the farther back we go, the more complex the physics become. When the universe was just a dozen minutes old, it was an intense soup of protons, neutrons, and electrons, still governed by the same physics that we use to understand nuclear bombs and nuclear reactors.


If we look back even earlier than that, however, things get really sketchy.

When we try to make sense of the universe when it was less than a second old, we have no theory of physics that can cope with the insanely high temperatures and pressures the universe experienced. All of our theories of physics break down, and we have no understanding of how particles, forces and fields operate in those conditions.
Birthing the singularity

Physicists can chart the growth of the cosmos using Einstein's general theory of relativity, which connects the content of the cosmos to its history of expansion.


But Einstein's theory contains a fatal flaw. If we follow general relativity to its ultimate conclusion, then at a finite time in the past our entire universe was crammed into a single, infinitely dense point. This is known as the Big Bang singularity.


The singularity is often framed as the "beginning" of the universe: But it's not a beginning at all.


Mathematically, the singularity at the Big Bang isn't telling us that the universe began there. Instead, it's telling us that general relativity itself has broken down, and has lost its predictive and explanatory power.


Physicists have long known that general relativity is incomplete. It cannot explain gravity at high strength or at small scales, known as quantum gravity. In other words, to fully understand the earliest moments of the universe, we need new physics.


A question for the ages

[MisterVeritis]

But we can only see so far. All of the galaxies that we can see are moving away from us. Physicists speak about space itself as one of the things that emerged from the Big Bang, but who can say what is going on in that part of the Universe beyond our view, perhaps even "outside" the Universe we know (or think we do)?

We can see almost 47 billion light years in every direction. In that space, the general rule that every galaxy is moving away from every other galaxy holds true.

Space-time emerged from the big bang. My favorite part of the theory involves inflation. It explains why our Universe is uniform.

[Standing Wolf]

We can see almost 47 billion light years in every direction. In that space, the general rule that every galaxy is moving away from every other galaxy holds true.

Space-time emerged from the big bang. My favorite part of the theory involves inflation. It explains why our Universe is uniform.

I guess I'm just trying to think outside the Bang.

[MisterVeritis]

I guess I'm just trying to think outside the Bang.

I don't know what that means.

[Just AnotherPerson]

Infinite implies that space and time continue forever forwards.

The science dictates a beginning, however, of the universe ... including time.

If you look just a bit closer you will find there is no beginning or end to anything. You imagine that a something has come into being, but that something already existed before it's so called coming into being. If I pour you a glass of water, you imagine that this is the birth of that cup of water. But in reality every particle from that cup of water already existed elsewhere before it became that cup of water. The same is true for everything in existence.

We designate things an existence based on our ideas. Reality cannot be predicated upon ideas of the mind. Beginning, and end are just ideas.

[Standing Wolf]

I don't know what that means.

Well that was mostly an attempt at stating it humorously, but the point I've been trying to make is that our cosmology proceeds from the assumption that what we think of as our "universe", and within which it is assumed everything that exists anywhere is contained, may only be one of a number, even an infinite number, of other expanding "universes" - separated by...? If "distance" isn't the right word, and "space" isn't either, maybe what lies between them is something we have yet to discover, even in theory. Whatever it is, however, prevents us, with our relatively primitive technology, from detecting those other "universes".