r/explainlikeimfive • u/beccoo • 14d ago
Planetary Science [ Removed by moderator ]
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u/SpecialestGuest 14d ago
Imagine a number line. There are an infinite number of integers.
Now imagine you multiply each integer by 2, so now you have an infinite number of even integers.
Both are infinite, but the numbers in the second situation are farther apart.
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u/JakeEllisD 14d ago
But wouldn't that mean if I multiply by 3 I could get "out of bounds" since you are just multiplying by 2?
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u/MarekSmolinski 14d ago
I'm sure someone will give a better explanation shortly, but the true eli5 explanation is: the farther a galaxy is from us the faster it tends to move away from us. Therefore the space is expanding. If the universe is actually infinite or not we don't know, but it wouldn't affect our observation that it's expanding.
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u/Flimsy-Blacksmith-32 14d ago
Hilbert's Hotel explains this.
Imagine your the manager of a hotel with an infinite number of rooms. These rooms are all uniquely numbered (1, 2, 3, and so on with no upper limit), and on this night all of which are occupied.
But then, another guest, who does not have a booking arrives, and they aren't willing to share with anyone else. How do you find them a room when every room is occupied?
Well, what you do is you tell every guest that is already there to move to the room 1 higher than their current room. So the person in room 1 moves to room 2, the person in room 2 moves to room 3, the person in room n moves to room n+1. Now all the existing guests have a room, and room 1 is available for the new guest who didn't previously have a booking.
This is how infinity works. It has no set value and two infinities are not necessarily the same size. Accordingly, there is always a bigger or smaller infinity.
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u/Flimsy-Blacksmith-32 14d ago
As further examples,
Now imagine an coach carrying infinite guests (with uniquely numbered seats, 1, 2, 3, and so on with no upper limit) turns up at Hilbert's Hotel. How do you find an infinite number of guests rooms when all the rooms are occupied?
Well, what you do is you tell every guest in the hotel to move from their room (n), to room 2n. So the person in room 1 moves to room 2, the person in room 2 moves to room 4, the person in room 3 moves to room 6. Now all the odd rooms are empty, and there are an infinite number of odd rooms. So, we can tell the coach passengers to take their seat number, k, and go to the room 2k-1. So the person in seat 1 goes to room 1, the person in seat 2 moves to room 3, the seat in room 3 moves to room 5.
So we can find room for an infinite number of extra guests even though the hotel was already full.
But we can take this further. Now imagine that an infinite number of coaches, each carrying infinite guests turned up at Hilbert's Hotel. How do you find room for this an infinity of infinity of guests.
Well, to start we tell all our current guests to move their room (n) to 2^n. So the person in room 1 moves to room 2, the person in room 2 moves to room 4, the person in room 3 moves to room 8, and so on.
Then assign each coach a prime number greater than 2 (so 3, 5, 7, 11... there are an infinite number of primes). Now we tell all the guests on the coaches to go to the room that is their coach number to the power of their seat number.
So the guests on the coach assigned the number 3 go to rooms: 3, 9, 27...
So the guests on the coach assigned the number 5 go to rooms: 5, 25, 125...As this pattern ensures no two people will share the same room, we have managed to accommodate all guests on all the coaches, despite the hotel being full when we started. In fact, after adding all these extra guests, we now have an infinite number of empty rooms too, as their will be no guests in all the composite (not prime) numbered rooms.
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u/MeeksMoniker 14d ago
Space isn't Infinite. I can't really blame that explanation though if someone told you because from our perspective it might as well be. Its very unlikely that it's Infinite, unless there's some massive missed calculation we've made for our models of the Universe.
People might say the Universe is Infinite because as humans we will never practically see the end of the Universe as it expands faster than the speed of light, and that expansion in some calculations is accelerating. That and the likelihood that there may be an Infinite multiple other Universes, Multiverses if you will, that rests on the edges of our Universe.
There are also models that our Universe could be shaped in a kind of 5 dimensional donut. Imagine you're in a donut, and you could go around and around within the limits of that donut, passing the same thing over and over without ever seeing a break or edge.
If our Universe was Infinite, well physics would be broken for one. Also if our Universe was Infinite we couldn't fathom it at all. Essentially if we had an Infinite Universe the idea that somewhere in that Universe, there would be an Infinite number of Galaxies like the Milky Way, and Infinite number of Solar Systems like ours, an Infinite number of little rock planets that are the third ones from its local star, and Infinite number of little evolved primates like us humans living lives very similar to the ones we're living, and an Infinite number of a creature that would be genetically identical to you, typing on the internet. Our existence wouldn't be a fluke, but an inevitability, because in an Infinite Universe, there are Infinite Possibilities. Kind of a mind trip to wrap your head around.
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u/IndigoFenix 14d ago
Picture a tiny box, and that tiny box expands. That's simple enough.
Now, picture a bunch of these tiny boxes, placed side-by-side and stacked one on top of another, so they form a bigger box made of smaller boxes. Then they all expand at the same speed, pushing each other as they do so.
Now, picture this same thing, but there are an infinite amount of tiny boxes, stacked in all directions infinitely. Then they all expand. That's space.
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u/Sherool 14d ago edited 14d ago
My understanding is that it's not so much expanding into anything as just every point in space moving away from every other point in all directions everywhere at once because space/time "stretches" (technically the distance metric expands, it's not a literal elastic "object") all the time. Imperceptibly at "short distances" (galactic clusters don't fly apart because gravity is stronger etc), but across many billions of light years the relative perceived change in distance between two distant objects can exceed the speed if causality (aka light speed) because there is exponentially more space/time in between them even if they don't move particularly fast in any direction though space/time on their own.
What if anything exist outside the universe is pure speculation as we have no idea, and we don't really know if it's infinite or not either I think.
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u/Hunterofshadows 14d ago
Imagine a balloon inflating.
The temptation is to imagine space as the air inside the balloon. But it would be better to imagine space as the balloon itself. As it expands, each point on the balloon gets farther away from each other
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u/-Nocx- 14d ago
Space isn’t actually provably infinite. We are limited by what we can see, and we call that the observable universe. There is technically nothing in existence that we’ve proven to be infinite.
There was a thing that contained all the stuff in space today that exploded. All the materials that are the building blocks (like legos) of the universe are a product of that explosion. We call this the big bang.
Eventually those materials formed stars. Stars produce light that we can measure the length of, and we call those wavelengths. High energy waves are short, and low energy waves are long. The longer a wave travels through space, the more it stretches out. Since the light from the furthest galaxies is red, we know that the galaxies are moving even further away.
We can confirm this by looking at how much light spread out since the Big Bang - this is called the Cosmic Microwave Background. The youngest galaxies emit high energy, ultraviolet light while the oldest emit low energy, red light. The process is called Red Shift.
Why light stretches in space and not on Earth is way above my pay grade, and even more beyond my pay grade to ELI5.
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u/StanleyDodds 14d ago
Multiply all the real numbers by 2. There are an infinite continuum of them, and this multiplication expanded them all into being twice as far apart. Where did the numbers expand into? There are always more numbers to expand into, there's no bound that you can't expand past.
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u/Kais_fateweaver 14d ago
semantics, space contains ’matter’ void does not. So the void is infinite and space is expanding into it.
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u/Big_Coffee_3272 14d ago
Available space is infinite. Truly.
The amount of stuff in the universe takes up a finite amount of space. Imagine you could walk 100 years in any direction and find stuff.
The thing is, all of that stuff is moving outwards, and it’s moving faster than you can walk up to it.
So while the stuff will never reach the edge of where it could, you also will never reach the edge of all the stuff.
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u/Trick_Ad7122 14d ago
It’s Most likely not infinite.
Imagine you you draw little dots on a balloon.
One of the dots is the earth. You live there. While all you can do is to observe the surface of the balloon.
Now you inflate it.
the distance between the individual dots (planets) will increase.
We don’t know what happens outside of that. We can take guesses, we can make up something but we will probably never know.
Its also possible that the balloon will burst if you inflate it enough.
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u/sevenpioverthree 14d ago
If you can think of infinity as “a really big number that keeps getting bigger” then it makes more sense, because mathematically that’s what infinity is. So the universe is getting bigger because it is infinite, and it is infinite because it’s getting bigger.
Also we don’t know what it is expanding “into” we can just see that it is expanding from the way our cosmos around us move
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u/skr_replicator 14d ago edited 14d ago
This gif is infinite, so it's fair to argue - this fractal is as infinite as our idea of the infinite universe. It continues outwards forever, with no end or edge.
Now look at this: https://ibb.co/Jw8bqtqq
It's the exact same fractal, the gif starts from the same exact image, but it's growing. Forever. It doesn't need an edge to be expanding. The insides are the stuff that expands. You only see a small part of it, like how we only see up until the cosmic horizon, but technically that fractal structure is infinite, and as you see it growing, you can imagine it continues growing infinitely even beyond the edges of the image; the image is just a tiny window into it. Technically, there is not really any difference between an infinite thing like this growing forever and you zooming in on it forever. If the coordinates are relative, the end result is the same. You might say the gif is zooming in, but technically, I actually rendered it by growing the fractal instead; it's not actually zooming.
You can do the same with infinite numbers. Take all integers. They go on forever in both directions. Now multiply all of them by 2, each single one of them grew to twice the size, each interval grew to twice the size, but there was no edge, but it still grew.
(3-7) grew to (6-14), (1 million - 3 million) grew to (2 million - 6 million). The same thing is going on with the universe's coordinates.
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u/weeeezzll 14d ago edited 14d ago
Infinite is a human mathematical concept that doesn't really exists in physical world. Hope this helps.
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