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zoicyte t1_j1dm3fs wrote

Reply to comment by a4mula in Can we truly know the age of the universe? by Geodad478

This is all wrong.

Galaxies are absolutely separating at rates faster than the speed of light. Or more specifically, space between galaxies is expanding faster than the speed of light, Altho the galaxies themselves are still moving at sublight speed. Light moves through this space at the speed of light however, and the furthest things we can see are approximately 13 billion light years away. We see them as they were 13 billion years ago however, “shortly” after the universe stopped being opaque. Those galaxies now however are actually more than 40 billion light years away now, but we haven’t had time to see them yet, for obvious reasons (the universe isn’t that old). The oldest thing we can “see” is the cosmic microwave background radiation - the last signal of the opaque universe which actually makes up a good chunk of radio static you can hear, and emanates from around the 400,000 year old point in the history of the universe.

All of this can be calculated using Einstein GR equations, and others sorted out in the subsequent 50 years.

Without getting into diffEQ, the math works out that all of space time was compressed into the same point (the big bang singularity) approximately 13.8 billion years ago, the total diameter of the universe that we can see now is actually closer to 80bly, but that’s just the part we can see now, the universe could be infinite and we wouldn’t know.

It’s a lot to take in, but you need to remember what we can “see” today is what existed when the light was emitted, not as it is “today”, and the farther away it is, the older that light would be, so the farther back in time you’re looking.

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a4mula t1_j1dn5dl wrote

I think we should all be careful when we're talking about right and wrong. Perspective is important.

You are correct that the space between galaxies is expanding at a rate that is faster than the speed of light. However, it is important to note that this expansion is not a violation of the laws of physics, as it does not involve the movement of matter or energy through space.

The expansion of the universe is a phenomenon that is associated with the expansion of space itself, rather than the movement of matter or energy through space. The expansion of the universe causes the distance between galaxies to increase over time, and this expansion can occur at a rate that is faster than the speed of light. This is because the expansion of the universe is not limited by the speed of light, but rather by the properties of space itself.

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zoicyte t1_j1do177 wrote

I don’t think I made any statements implying it was breaking any laws of physics?

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Ennara t1_j1e1akv wrote

>the space between galaxies is expanding at a rate that is faster than the speed of light. However, it is important to note that this expansion is not a violation of the laws of physics, as it does not involve the movement of matter or energy through space.

Oh god, this breaks my brain. The amount of space between galaxies is expanding, but the galaxies themselves aren't moving as a result of the expanded space between them? I'm not saying you're wrong, but god dang I can't wrap my head around how that's actually possible.

The only vaguely coherent thing I can think of is like... a piece of taffy, where the two galaxies are sitting on the edges and you stretch the middle downwards. So the amount of space the taffy occupies increases, but the galaxies don't actually move. But I don't think that's accurate, because if space between us and a distant galaxy is expanding, then the distance increases which it doesn't in the taffy explanation... And I'm back where I started.

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a4mula t1_j1e1s1h wrote

If you read the earlier analogy with the cake.

We can pretend, because its just an analogy. That space in the analogy is air in the cake.

The molecules of the cake aren't growing or moving. It's only that the air in between them continues to grow.

It will ensure that the cake molecules end up with greater distance between other cake molecules.

But it's not because the cake molecules moved. It's because the air in between them grew.

Now this is just pretend, because air is not space. Air is molecules too. So I don't want to confuse that.

But it does fit the analogy.

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Ennara t1_j1e40x2 wrote

Yeah, I sort of get that, I think at the core of it all I'm just having trouble wrapping my head around the concept of increasing the amount of space between two objects without moving them. Using the cake analogy, I'm finding it difficult to understand how the air molecules move in such a way to take up more space without pushing the things that already occupy that space out of the way. I can accept that they are based on the studies and testimony by people far smarter than I am, but my brain is pitching a fit because I'm struggling to grasp the 'how.'

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a4mula t1_j1e5iic wrote

That's okay. I mean these are Big topics. It's taken our species millions of years of slowly building up to this point right now that we have the understandings we do of them.

It's not easy. For anyone. Not for you, Not for me. Not for Einstein.

We're not born innately knowing this, we're educated about it. If they are concepts that we find interesting, perhaps we consider them. It's only through this education and consideration, not just the education itself, that we come to understanding.

Not everyone has the time or inclination to consider these topics, and that's okay.

But for those that do, understanding will grow in some type of correlation between the interactions of the education and your consideration of.

Ask for analogies, they're great tools of abstraction. It takes these difficult concepts out of the realms of mathematics, and puts them squarely into terms we can better understand, everyday language. Math is important, but if it's not a language spoken by us, it's not helpful.

Einstein's brilliance was never that he was a great mathematician. It was his ability to break down very complex thoughts into stories he could understand.

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a4mula t1_j1eafan wrote

I wanted to add another reply here.

What If I wanted a really cool expandable cake like we talked about and asked you to make it for me.

But I've got a very special request.

After you bake the cake and add the frosting. I'd like to add a special flavoring. So that anyone can make this cake taste the way they'd like.

See if you can figure this out. Can I do this? What do the actual interactions look like? If I dropped the flavoring into one part of the cake, how would it distribute?

Would it be evenly? Could it ever fill the entire cake, assuming the cake never stopped growing? How would it travel from one cake molecule to the next?

This will help you to understand concepts like speed of light, and why we can't pass information faster than it.

It'll help you to understand localized events and how they interact with portions of the universe, but never the entirety of it.

Think about the relative movement. Without the flavoring now. The space between two cake molecules will always be a different relationship depending on the location of where they exist in relation to one another.

Two cake molecules side by side will always experience the same relative separation. But two molecules separated by the entire cake will always experience greater total separation because all the spaces of molecules growing in between them are cumulative.

We can pass flavor between two cake molecules, indefinitely. But assuming the cake never stops growing, what you'll find is the ability to spread the flavor becomes a function of the overall growth rate of the cake as a whole, meaning it can never keep up and that the total amount of the cake that is flavored in respect to the total cake, will always decrease.

That's odd. Because we're still getting more cake that is flavored. It's just that the amount we get will always represent a smaller percentage of the whole.

edit: We've taken our analogy in a very specific direction. One of infinite inflation of a mostly spherical object. Our universe doesn't need to meet those criteria. This is just one way to consider things. If the universe has different parameters, the interactions would inherently be different. What if our cake was really a doughnut? What if it were just a 2d plane of 3d information?

Keep these things in mind, as there are clear limitations to locking our thoughts into the ability of analogies to represent ideas.

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ramsncardsfan7 t1_j1e0y0q wrote

Why do I see experts saying the universe wasn’t actually a singularity at the time of the Big Bang?

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zoicyte t1_j1e1yw1 wrote

Well strictly speaking a singularity is just a breakdown in the known laws of physics. something has to be down their, we just don’t know really what, or how it behaves.

Why did expansion start? Where did it all come from? What came “before”, to the extent that statement even has any meaning? These questions are at the very bleeding edge of theoretical physics and aren’t really testable yet.

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[deleted] t1_j1e2uq7 wrote

I wonder whether they ever will be. Our ability to peer back in time relies entirely on what we can see and the radiation we can capture and analyze. Looking back far enough, it all becomes opaque because "first light" hadn't happened yet. Perhaps some new tech will throw the doors open some day, but if we cannot see past a certain point, and that point happened after the "bang," then we will never know what came before the opaqueness.

For that reason, I don't know for sure that the singularity has any merit. If we run the clock backwards we get a singularity, but since we can't see past a certain point, we don't actually know whether singularity is a real concept.

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zoicyte t1_j1e3hmo wrote

It’s not just about looking “out there”, a lot of the early-universe physics are probed in high energy particle colliders. It’s mostly about understanding quantum effects at that point.

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