Finite Space?

You are thinking about this incorrectly. There is no "edge" of the Universe, meaning you can't get to the absolute furthest star and look back and see the Universe and look forward and see "nothing" because that's not what's actually going on. You are sort of asking the equivalent of "If I went to the furthest point on the surface of the Earth and looked forward what would I see?" Well the answer is more Earth.

This is a common misconception when discussing the Big Bang Theory. Media almost always portrays it incorrectly as a massive explosion with the Universe rapidly expanding outward from a single point. That is not what happened. The Big Bang happened everywhere at the same time. Remember earlier we said that the Universe is "everything" and the Big Bang happened "everywhere" at the same time. So the Universe did not expand outward from a single point but rather "everything" (Universe) is expanding "everywhere" at the same time.

In order to understand this better a few points need to be made. First there is a difference between the "Observable" Universe and the actual whole Universe. The Observable Universe is the part of it what we here on Earth can see and the "edge" of that is as far as light has been able to travel to us here since the Big Bang. It's roughly 93 billion light years in diameter with a radius of half that. So, here on Earth (or in orbit around here) if you point the most powerful telescope possible in any given direction the absolute furthest you can see anything is roughly 46.5 billion light years away. The light from anything further away than that will never be able to reach your optics because the Universe itself is expanding faster than the speed of light. That that is the "edge" of our Observable Universe.

Now, if you magically teleported to a star at the absolute edge of our Observable Universe and looked "forward" what you would see is more Universe and if you turned around and looked "back" then we here on Earth would be the "edge" of YOUR Observable Universe. But us here on Earth can look "back" and see more Universe but YOU can't at your new star because no light from anything "behind" us here on Earth will ever reach you at your new star for the same reason why the light "in front" of you at your new star will never reach us here on Earth.

This keeps going on and on regardless of if you keep teleporting to the edge of your current Observable Universe. The Universe itself looks the same from all perspectives but the portion of if that YOU can see depends on where you are for the aforementioned reasons.

There is no "edge" of the Universe just like there is no "edge" of the surface of the Earth. If the Earth began to just magically start increasing its size by expanding then you can't just fly from NYC to Sydney and look "forward" and see "nothing" then turn around and see "land". If you are in Sydney and look in 360 degrees then you see Earth all around you, same as if you are thousands of miles away in NYC, and if the Earth just tripled in size overnight it still wouldn't change the fact that no matter where you are on Earth you can still turn 360 degrees and see Earth all around you instead of turning 180 degrees and seeing "nothing".

Mind you, no the Universe is not a sphere that was just the best way I could think of to explain this. The Universe is actually believed to be flat. Alright so if it's flat and not a sphere then it has an edge. No, it doesn't. The reason is because as we discussed before the Big Bang didn't happen at a single point and expand outward on the flat plane, the Big Bang happened everywhere at the same time. So the reason why you can't teleport to the "edge" of this flat plane and see "Universe" behind you and "nothing" in front of you is because the Big Bang happened at your "furthest star" just like it happened everywhere else.

"Everything" expanded "Everywhere" at the same time. Your "furthest star" is included in both "everything" AND "everywhere". You can't go anywhere that the Big Bang didn't happen because it happened "everywhere". So no matter where you go in the Universe, if you look 360 degrees in any direction you will see more Universe.

So can you magically travel faster than the Universe itself is expanding and catch the "edge" of it? Nope, because remember the entire Universe was subjected to the Big Bang at the same time and is also subject to the expansion from the Big Bang. So as long as you are IN the Universe (you have to be, you can't leave it it's "everything") then you are subject to expansion and the effects of the Big Bang. So even the furthest star away from you right now is subjected to what happened with the Big Bang. And the furthest star from that as well, and so on and so forth.

So even if you magically jumped faster than the Universe itself is expanding and found a star, you're still IN the Universe, and the Big Bang happened THERE just like it happened "everywhere" else in "everything" which is the Universe that you are still in.

Only way to do what you are asking is to magically get "out" of the Universe and watch it. But you can't do that because there is no "outside" of the Universe because the Universe is "everything". In pseudoscience they have Multiverse stuff but it's not really backed by any actual evidence nor supported by many reputable scientists. So in that case I guess you "could" go to another Universe and maybe watch ours expanding but there is absolutely no scientific evidence supporting such things and multiverse theories are basically nothing more than people fantasizing about things.

 

Well the Universe isn't expanding between you and your computer or the Earth and Venus because of gravity. At the local level gravity is stronger than the force of expansion, and by local level I'm talking about our local group of galaxies. Expansion is happening on a larger scale than that. Earths gravity keeps you on Earth, The Sun's gravity keeps the Solar System together, Sagittarius A (the huge black hole at the center of the galaxy) keeps the Milky Way together, and the combined gravity of our galaxy and our neighborhood galaxies keeps all of our galaxies together in the Local Group. The rest of the galaxies are expanding away from us.

 

Not all of them but a lot of them are in clusters. There are some galaxies that are out there by themselves and not part of any cluster. These clusters do have the combined gravity to overcome the expansion of the Universe, however, this is on a small scale in cosmic terms. A cluster only counts as a cluster if the gravity within it is enough to keep all of the mass within it bound together, once the effects of expansion are recognized within the cluster then it's no longer a cluster.

In the past we basically just kept going up in scale. We had the Solar System, then Milky Way Galaxy, then Local Group, then Virgo Supercluster, then Laniakea Supercluster. In reality Universal Expansion starts to take effect past the Local Group and while the effects of combined gravity are measurable within the Virgo Cluster, Expansion is greater and the galaxies outside of our Local Group are effected more by expansion than gravity, therefore they aren't technically "clusters" anymore. Eventually the rest of the Virgo Cluster and beyond will expand away from us while the Local Group is will stay relatively intact.

It's not just the collection of mass that keeps the Local Group bound together it's also dark matter. The effects of dark matter have been observed in a nearby galaxy cluster called the Bullet Cluster. Gravity is strong and causes gravitational lensing. The gravity within the Bullet Cluster does this but the lensing effect is stronger than it should be based on the amount of mass in that cluster so scientists concluded that it must be the gravity of dark matter and energy that is causing this additional lensing.

Basically the Local Group and all other galaxy clusters do not contain enough mass to support the gravity required to keep them bound together. Something else is in there as well which is dark matter. Without dark matter than there would be no galaxy clusters because the expansion of the universe would pull them all apart.

 

Yes the gravity of dark matter is what contributes to keeping galaxy clusters together. To break it down basically what's going on is that gravity is used to "weigh" stuff in space. For example Jupiter has a mass of 1.898 × 10^27 kg. It "weighs" that much. We obviously cannot put Jupiter on a giant scale and weigh it but we know that due to the planets gravitational effects on things near it such as it's moons and the probes we send there. We "weigh" galaxies but observing the gravitational effects of the stars within the galaxy roughly the same way we "weigh" planets based on their gravitational effects of their moons or our probes. We also know the strength of gravity vs mass. Basically if something "weighs this much" then the gravitational effect on nearby objects should be "this much". We have observed in other galaxies that they "weigh this much" but it's gravitational effects are greater than they should be. If galaxies contained only the gravity and mass (weight) of the observable matter within them (stars and stuff) then they wouldn't "weigh" as much as we see that they do and wouldn't have the gravitational effects that they do. So scientists have concluded that "something else" is in there contributing to the "weight" (mass) of these galaxies. Dark matter.

Computer simulations of galaxies using only their observable matter have concluded that they would not "stick together" if there wasn't something else in there.

Dark matter is just a term used by scientists to basically say "we know it's there but we don't know what it is and we can't see it".

From what I understand, and I may be wrong, dark matter is present in the Solar System but it's so negligible that it's undetectable. Basically it has no real effect on the Solar System, the Sun controls us around here.

As to your second point, objects do not become weightless in space. Remember when we said mass determines gravity? While "not too far from Earth" as in orbit, you "weigh" roughly the same as you did on Earth, the Earth's gravity doesn't drop off that quickly, you weigh roughly 90% what you do on the Earths surface. What's happening when you see astronauts floating around is that they are falling towards the Earth all the time but missing the Earth. "Orbit" in layman's terms is tossing something into space at a precise speed to where it will "fall" towards the Earth equal to the rate at which the Earth is moving away from you along it's orbital path. Rocket launches are very precise, you can't just launch one at random and have it stay in orbit, the Earths gravity WILL drag it back down to Earth. You have to launch it at a precise speed to ensure that it falls back to Earth at the same rate that the Earth moves away from it or else it will fall back down to Earth.

So when you see Astronauts "floating" around in space weightless, they aren't. Everything up there is just in a constant state of freefall back towards the Earth but the Earth is also moving away along it's orbital path at the same rate that they are "falling". So they appear to be floating and weightless. Think of it as skydiving and the Earth itself is also skydiving with you, you never hit the ground because the Earth itself is falling at the same rate you are so you just sort of stay there floating.

 

The answer to the question about the singularity is that we honestly have no idea. "Singularity" isn't so much a "thing" as it is a placeholder word for when the mathematics no longer make sense. Scientists are working very hard to uncover what happened at exactly t=0 (start of the Big Bang) but they haven't figured it out yet. We know what happened during the Planck Era approximately 1 gigabazillion fraction of a second AFTER the Big Bang (I made that term up 10^-43), but we don't know what caused it all to start.

There are some theories about white holes, I honestly don't know much about that theory and haven't looked very much into it.

Dark energy does exist everywhere the effects of it are just minimal in some places such as in our own Solar System. Dark Energy is what is driving the accelerated expansion of the Universe but in some cases the collective gravity of matter and dark matter is enough to overcome the rate of expansion such as in galaxy clusters.

There is an equilibrium to where stuff in space will orbit the Earth by falling with the Earth around it's orbital path. The reason why you can't just jump in the air and stay there is because believe it or not you (and everything else on the Earth) is actually moving along the Earths orbital path at the same speed as the Earth is because you are on the Earth travelling with it.

Think about it like being on an airplane. On a commercial airline if you get up out of your seat and move into the isle you aren't slammed into the back of the aircraft. You can jump around and everything just fine and you don't move. The reason is because the airplane is flying at 600kts through the air and you are flying at 600kts as well while inside the airplane. This is also why airplanes can actually fly around the Earth and don't get "stuck" up there with the Earth spinning beneath them when they leave the surface. The Earth isn't just the ground it's everything within the Earths atmosphere including the sky. So even airplanes are travelling WITH the Earth along it's orbital path.

Have you ever heard of the old saying about jumping at the last second in an elevator that is freefalling and it will save you? That's not true, the reason is because if the elevator cable snaps and it's falling with you inside then you are falling at the same speed as the elevator. So if you jump at the last second before impact then you are still going to slam into the bottom of the elevator at nearly the exact same speed as it was falling.

 

It depends on where you are in orbit. In a perfect vacuum then no you would never fall back to Earth as long as you are travelling at the same speed as the Earth is around it's orbital path. The reason stuff falls back to Earth in orbit is because a lot of stuff up there is in low Earth orbit which isn't really very far away.

Picture the ISS for example. They have to routinely fire the jets on that thing to keep it from falling back to Earth. The reason is because of it's relatively close proximity to the Earth. Even in space at that low altitude the Earth's upper atmosphere has a tiny effect on it. The upper atmosphere is slowing down the ISS ever so slightly due to a very tiny amount of drag. So over the course of time the ISS slows down and starts falling back towards the Earth requiring some thrust to speed it back up again.

Think of it like a tether ball on a playground. When you smack the ball really hard it spins around the poll and stays spinning around the poll due to centripetal force. Once it starts to slow down it starts getting closer to the poll until it eventually hits the poll. Stuff in orbit is the same way only it's gravity and not a string that's providing that centripetal force. If you could keep your tether ball going at the same speed as when you just smacked it then it would forever swing around the poll at that altitude. So as long as the stuff in space maintains that perfect velocity then it will forever stay up there swinging around the Earth. Just don't get too close to something that can act on it and slow it down.