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Is time an illusion?
closed account (367kGNh0)
| Time is how the universe stops everything happening at once. |
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| The entire point of my previous post was explaining why that's not the case. |
You agreed on it before, but lets go back to the cubic space analogy. If space disappeared, what would be there? A void? No, a void would mean there's volume, meaning there is space. So the time aspect of that spot would remain, but where would it be? Would it be a point that may or may not exist? What's to distinguish that time from literally nothing?
| You're applying a double standard |
Perhaps, I'll argue a few more points a bit more before giving into your view. If we assume that time is simply another dimension of space (as many do), then we can go back to my argument of not being able to have time without the dimensions of space before it. Lets say I had an object in spacetime. This object is a 4D object in space time. As we know, to exist in this universe as an object, you need to have 3 dimensions of space. So lets say we take away a dimension and you go to a 3D object, did you forfeit a dimension in time or space? Can you become a 2D object moving through time?
The nice thing about this argument is that we can assume the object was 4D until that moment. If I were to suddenly lose a dimension of myself, would I become a 3D physical object existing in space but not time? (meaning I would likely stop existing since I don't exist in time) Or, would I become a 2D object in space that moves through time?? Seeing as how it would be impossible to exist as a 2D object in a 3D universe (there will always be a 3rd dimension of you, no matter how thin), that theory sounds dismissable.
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| You agreed on it before |
| So the time aspect of that spot would remain, but where would it be? |
| Would it be a point that may or may not exist? |
| What's to distinguish that time from literally nothing? |
| I'll argue a few more points a bit more before giving into your view. |
| If we assume that time is simply another dimension of space (as many do) |
| Lets say I had an object in spacetime. This object is a 4D object in space time. As we know, to exist in this universe as an object, you need to have 3 dimensions of space. So lets say we take away a dimension and you go to a 3D object, did you forfeit a dimension in time or space? Can you become a 2D object moving through time? |
If God (I don't know who or what else could do such a thing) came down from Heaven and flattened my computer into a less dimensional object, I have no idea what would happen. God's God, so He can do whatever he wants, I guess.
If we're talking within the context of an abstract 4D universe, you can flatten a hypercube any way you like. If you flatten it along the time axis you'll get a normal cube that would exist for a single instant of zero length. If you flatten it along one of the space axes you'll get a plane that would exist for the same amount of time that the cube existed.
By the way, it's not clear to me that spatially 2D objects are impossible in the universe (even our own). 2D objects made of matter are obviously impossible, but just 2D objects in general, I don't think so. At least an argument would have to be made to justify it. Like I said, elementary particles appear to have no dimensions, so a 2D object seems easier to me.
EDIT: By the way, check this out: https://www.youtube.com/watch?v=0t4aKJuKP0Q
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| Do you mean another dimension of spacetime? It's not another dimension of space. We can't move forwards and backwards in time like we can in space. |
Minkowski space - it can be beneficial to view time as another dimension of space at times. I was going to making a point with that, but I didn't.
| It's not my intention to fatigue you into agreeing with me. |
Not that, your points are making sense is all.
| By the way, it's not clear to me that spatially 2D objects are impossible in the universe (even our own). 2D objects made of matter are obviously impossible, but just 2D objects in general, I don't think so. |
0D things exist since they are massless. If you had something that was 2D, it would surely have mass in order to take up 2 dimensions, meaning it wouldn't exist in this universe.
| I issue I have with this thought experiment is that you're first asking me to imagine a physically impossible event (flattening a 4D object into a 3D one), and then asking me to answer what would happen in the actual physical universe. |
I suppose, but I think we've been doing that for a while! Either way, it would seem to make more sense that you can't remove space and keep time. However, I do see your arguments as well. Perhaps there's no way to know at the present time.
| By the way, check this out |
Yes, I've learned about 4D objects on my own time before. A few ways to see a 4D object is to see the shadow cast by it or to "unfold" it. For example, a tesseract would simply be 6 cubes when seen "unfolded", same as how a cube would be 6 squares when unfolded. Another example is seeing how the 4D object would behave as a shadow, the same as how we can cast a shadow of a cube so a 2D person would be able to see it.
However, this 4D and 4D with space and time are not the same thing.
| Minkowski space - it can be beneficial to view time as another dimension of space at times. |
| If you had something that was 2D, it would surely have mass in order to take up 2 dimensions |
| Either way, it would seem to make more sense that you can't remove space and keep time. |
| Yes, I've learned about 4D objects on my own time before. |
| For example, a tesseract would simply be 6 cubes when seen "unfolded", same as how a cube would be 6 squares when unfolded. |
A 4D shape with six cubes would be an infinite cubic prism, I think.
| Minkowski space is a formalization of spacetime. Time is still not a spatial dimension, although it is a dimension of spacetime. |
Yes, but the 4th dimension of time is measured in distance in Minkowski space, as if it were another dimension of space. Not that it is, but that it can beneficial to think of it as such sometimes.
| Oh? What's the volume of a 2D object? |
That's a trick question and I think misses the point. Lets say we did have a 2D object, because we can't take volume it doesn't exist with mass? And lets think about what would happen if we suddenly appeared in a 4D universe. It would be the same as if a 2D person appeared in ours. We would seem infinitely thin in one dimension and we wouldn't have "hypervolume". But does that mean we don't have mass?
| A tesseract would be 8 cubes (or "cells") unfolded...A 4D shape with six cubes would be an infinite cubic prism, I think. |
Yes, 8, my bad. I'd assume it would simply be a different object all together. If we only got 4 squares and tried to make a cube, it would simply be missing 2 sides, but it wouldn't become and infinite square. At least I don't think so.
| Don't get me wrong, we can imagine what such a universe would look like dimensionally, but if we ask about the physics of such a universe, it's all up in the air. Beyond the very basics, like "there is movement" or "there is no movement", the physics can be anything you want, because we just don't know. |
I suppose this means we can't find out. Your arguments made sense and so I'll refrain from assuming time exists within space, but it does still make sense to me.
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closed account (367kGNh0)
| That's a trick question and I think misses the point. Lets say we did have a 2D object, because we can't take volume it doesn't exist with mass? And lets think about what would happen if we suddenly appeared in a 4D universe. It would be the same as if a 2D person appeared in ours. We would seem infinitely thin in one dimension and we wouldn't have "hypervolume". But does that mean we don't have mass? |
If you throw a baseball into a blackhole, it will be interpreted as 2D. According to your logic that ball has a volume of zero.
| Yes, but the 4th dimension of time is measured in distance, as if it were another dimension of space. |
| Lets say we did have a 2D object, because we can't take volume it doesn't exist with mass? |
The closest approach to an argument I have that an elementary particle (such as a quark) exists probabilistically in a region of 3D space, and if you try to take the probability of it existing in a zero volume (such as a point, a line, or a plane), you get zero probability.
| If we only got 4 squares and tried to make a cube, it would simply be missing 2 sides, but it wouldn't become and infinite square. |
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| Distance is a property of any dimension, though, not specifically of space. An offset in a buffer is a distance, but not in space, in bits. |
I suppose, but the unit of measurement matters. In time, we don't say we're 3 yards from yesterday. But in Minkowski space, you get a unit of distance when speaking about time.
| was going to make the argument that mass requires matter and matter requires volume, but after talking here in the office with a physicist, I'm gonna have to go with "we don't know if mass can exist in zero volume, be it zero- or one-dimensional". |
In this universe, matter does require volume. In a 2D universe, I'd assume it wouldn't require volume, only area. But for something in this universe to use up 2 dimensions of space, it would need SOMETHING there to fill that space. That would require mass, but not any mass that could exist within our universe, hence why I'd say a 2D object wouldn't be able to exist.
To me, it's either you have no mass and are 0D, or you have mass and therefore MUST have 3 dimensions. I don't think an in-between stage can exist.
| Fair point. I guess I was thinking about partitioning the space into an enclosed n-volume. |
Yea, I've gotten tripped up a lot too trying to imagine 4D objects.
| If you throw a baseball into a blackhole, it will be interpreted as 2D. According to your logic that ball has a volume of zero. |
Why would the baseball become 2D? Blackholes are 3 dimensional. Once you go inside the black hole your mass might become 0D for a split second when you reach the singularity, but who knows. Certainly no one knows what happens inside of a blackhole.
closed account (367kGNh0)
| Why would the baseball become 2D? Blackholes are 3 dimensional. Once you go inside the black hole your mass might become 0D for a split second when you reach the singularity, but who knows. Certainly no one knows what happens inside of a blackhole. |
Got it from kurzgesagt. We know black holes deterierate over time.
closed account (z05DSL3A)
Do you actual think a black hole is a hole rather that an incredibly dense lump of matter?
| In time, we don't say we're 3 yards from yesterday. |
| In a 2D universe, I'd assume it wouldn't require volume, only area. |
Sure, whatever. Fairy wings can be any color you like.
| But for something in this universe to use up 2 dimensions of space, it would need SOMETHING there to fill that space. |
Perhaps the word "object" is confusing. When I say "object" I'm not referring to something solid, or even necessarily tangible. When I talk about an object I'm talking about anything whose existence can be distinguishe d from its non-existence.
Consider the path of a photon. That would be a 1D object in spacetime. We can't measure the path of a measured photon directly without altering it, but we can infer it by measuring the path of a stream of photons.
So what would be an example of a 2D object in space? Well, since you guys started talking about black holes, actually an event horizon is two dimensional at any given time (it's 3D in spacetime, though). The region of space where a photon can only just orbit the black hole without falling in and without escaping out has no thickness, but it does have surface area. It will usually be some kind of oblate spheroid.
| Well, c suggests an equivalence between distances in time and distances in space. You would actually be about 25.9 billion km from 24 hours ago. |
Well, that proves my previous point of time being treated as a dimension of space in some aspects.
| Sure, whatever. Fairy wings can be any color you like. |
If we don't try to imagine these things we'll never get anywhere?
| Perhaps the word "object" is confusing. When I say "object" I'm not referring to something solid, or even necessarily tangible. |
I understand, the issue is that what could be NOT tangible or a solid yet take up 2D space? The only way to take up dimensions of space is to have mass. And if you have mass, you therefore have 3 dimensions.
| So what would be an example of a 2D object in space? Well, since you guys started talking about black holes, actually an event horizon is two dimensional at any given time (it's 3D in spacetime, though). |
Black holes are 3 dimensional in space.. They are spheres, but nothing reflects off them so you can't see depth and they appear to be 2 dimensional. But as you travel around the black hole, you'll see that it looks like a circle from all angles, hence a 3D sphere.
The only "2D" aspects of a black hole have to do with relativity. At the event horizon, to an outside observer, things never really fall into the black hole, they get infinitely closer then disappear, never seeing them fall inside. And "infinitely closer" means the space they'd take up would be 2D to an observer. Anyone falling inside a black hole wouldn't become compressed to a 2D object because time is moving differently for them. To them, they didn't spend an infinite amount of time approaching the event horizon.
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| Got it from kurzgesagt. We know black holes deterierate over time. |
Sorry, didn't see your post right away. But I think my above paragraph addresses what you've said as well.
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| Well, that proves my previous point of time being treated as a dimension of space in some aspects. |
| If we don't try to imagine these things we'll never get anywhere? |
| Black holes are 3 dimensional in space.. They are spheres, but nothing reflects off them so you can't see depth and they appear to be 2 dimensional. But as you travel around the black hole, you'll see that it looks like a circle from all angles, hence a 3D sphere. |
I'm talking about the event horizon. The event horizon is a boundary between two regions of space. Light within can only go further inside the black hole and light outside can still escape out. A non-rotating black hole could have a spherical event horizon, and if a photon were to graze it just right, the photon could get trapped by the event horizon, and neither escape out nor fall in. It would be an unstable and easily disturbable orbit, though.
| You can treat it as a dimension in that you can measure lengths using consistent units, but that's about where the similarities end. You can't rotate objects perpendicularly to the time axis (all rotations must be parallel), or shift their position along that axis. |
Was never going to go that far with it. It was a point with a flaw in it and so I didn't make it.
| Where will we get by imagining physical laws of hypothetical universes, which we have no way to test the accuracy of? And I don't mean test the accuracy to reality, I mean test the accuracy even within our own minds. |
I suppose, but for the sake of argument you have to bring impossible things up sometimes, simply for the purpose of making a statement. Maybe not possible to test, but it's not like this debate has had only testable theories throughout.
| I'm talking about the event horizon. The event horizon is a boundary between two regions of space. |
The event horizon is simply the point where nothing can escape the gravitational pull of the black hole. If you want to try and pinpoint that location, then sure, you can perhaps call it a 2D position in the sense that its a distance so small that you can neglect it from 3D discussion. But this is not in any sense an object existing in 2D in our universe. This is a concept which can be defined as 2D. But in the real world, there is simply a point in which the gravitational pull makes light speed not as fast as the black hole's terminal velocity. That region is simply where, when crossed, light cannot escape. If we try to indicate the region, we end up with something almost 2D since the region between the photon sphere and event horizon is small.
However, again, this is only true because we are trying to show a concept, not because there's actually something 2D. The divide showing the event horizon can be compared to seeing when a 0 turns into a 1. You say, it's either a 0 (hasn't crossed the event horizon), or a 1 (has crossed the event horizon). There's no "halfway" crossed into the event horizon. You either have crossed it or you haven't, there's no wiggle room. Same with the event horizon, meaning when you try to visualize it, it becomes a 2D surface because you've either crossed it or you haven't.
For example, if at an infinitely precise coordinate in space a radio signal "fully" dies out and I try to reach that coordinate. I've either passed it or I haven't reached it. The only way to be in the coordinate is to be in the middle of it which isn't how it would work in a black hole (light gets sucked in immediately). But to try and see whether I've passed that infinitely precise coordinate or not, you'd have to make a 2D plane, because there's no concept of thickness - after that coordinate there's no radio signal, before it there is. But there's nothing 2 dimensional about any of it, it's our concept which requires 2 dimensions to visualize.
| The divide showing the event horizon can be compared to seeing when a 0 turns into a 1. You say, it's either a 0 (hasn't crossed the event horizon), or a 1 (has crossed the event horizon). There's no "halfway" crossed into the event horizon. You either have crossed it or you haven't, there's no wiggle room. |
But it doesn't matter that nothing can ever be stably inside that region. That region exists. It has a precise physical definition (light will not escape but will not necessarily fall further in).
| But there's nothing 2 dimensional about any of it |
Yes, you can never never put your spacecraft exactly on the sphere. No matter how small you make the antenna, it has non-zero volume. So it's either picking up the signal, and therefore inside the sphere, or not picking up the signal, and therefore outside it. But, again, that's my point. That's exactly what we would expect to see when dealing with 2D objects. If you could park your ship directly on the sphere it would mean one of two things: either you're an invader from Flatland, or the sphere isn't a sphere at all, but a shell.
closed account (367kGNh0)
| Do you actual think a black hole is a hole rather that an incredibly dense lump of matter? |
I didn't say that.
| If you're right on the event horizon you haven't crossed it. You're on it. Obviously a physical object can't be exactly on the event horizon, that's my point. It's a two dimensional surface with no thickness. |
Exactly my point, you're either before or it beyond it. The point here is that if you wanted to map out the event horizon for the entire black hole, it would become a 3D figure you'd look at surrounding the black hole. The only time the event horizon is 2D is when you are looking for it off of a specific point from the black hole.
| So it's either picking up the signal, and therefore inside the sphere, or not picking up the signal, and therefore outside it. But, again, that's my point. That's exactly what we would expect to see when dealing with 2D objects. If you could park your ship directly on the sphere it would mean one of two things: either you're an invader from Flatland, or the sphere isn't a sphere at all, but a shell. |
I think I understand. So the fact that it's not intractable somehow adds validity to its 2D property? The issue here is that, again, it's a concept rather than anything else. If I was floating into space and passed by a planet, I'm either too far to get sucked in or I am too close and get sucked in. The "point" at which I will get sucked in can be represented by a 2D plane or even a dot (1D) for every point along the "event horizon" that I'm passing near.
But what all this is to show is that the event horizon is like an on and off switch, either you've passed it or you haven't - there's no range. If you could somehow see all the event horizons of a black hole, you'd see a sphere encompassing the black hole, not a 2D figure.
However, this is still beside the point. That "point" where the event horizon exists has thickness, from the starting point all the way until you reach the singularity. However, you traditionally only want the exact point where it begins and on a certain point, where there can't possibly be any thickness. So the only reason there's 2 dimensional anything is because of how we are using the concepts and what we are trying to show, not because there's actually something 2 dimensional there.
| The point here is that if you wanted to map out the event horizon for the entire black hole, it would become a 3D figure you'd look at surrounding the black hole. |
https://en.wikipedia.org/wiki/Sphere
| a sphere [...] is a two-dimensional closed surface, embedded in a three-dimensional Euclidean space |
| If I was floating into space and passed by a planet, I'm either too far to get sucked in or I am too close and get sucked in. The "point" at which I will get sucked in can be represented by a 2D plane or even a dot (1D) for every point along the "event horizon" that I'm passing near. But what all this is to show is that the event horizon is like an on and off switch, either you've passed it or you haven't - there's no range. |
So, which part of this do you disagree with? If a point particle can never exist on the event horizon even for single instant of time then either space or time are discontinuous. If it doesn't have zero thickness then we're not talking about the black holes of general relativity anymore.
| However, this is still beside the point. That "point" where the event horizon exists has thickness, from the starting point all the way until you reach the singularity. |
| Do you agree with this?... If you can occupy it at all, then it must be a region of space that exists, right? And it has zero thickness, because an infinitesimally short time before you were before it, and an infinitesimally short time after you will be below it. |
Yes, you have to pass through it obviously. But you move through 3 dimensional space. If you try to isolate a certain amount of space mathematically, you can certainly come up with an infinitely thin slice that would be considered 2D, but that space doesn't exist as 2 dimensions outside of your calculations is what I'm saying. If you tried to make a 2D plane for every possible position in a region of space, you'd have an infinitely long task ahead of you because you'd constantly have a region with 0 thickness, and it would be as if you didn't map the spot at all. Nothing 2 dimensional like this actually exists beyond the math used to explain a concept.
| So, which part of this do you disagree with? If a point particle can never exist on the event horizon even for single instant of time then either space or time are discontinuous. If it doesn't have zero thickness then we're not talking about the black holes of general relativity anymore. |
Perhaps I misspoke. The particle obviously travels through the point of the event horizon. The issue is nothing about this. 2D models of the event horizon are perfectly fine because you want to know where you'd pass it (which only needs 1 or 2 dimensions to represent) at a certain point. But that how we represent it in our calculations of this concept, it's not because there's actually a 2 dimensional object (with or without mass) existing there.
| ??? |
Lets go the planet analogy again (lets assume Earth). At some point, I'm too close to escape the pull of the planet. But there's a range to that. If I'm on the planet, then I obviously can't escape it. If I'm a few miles above the planet, I still wont escape it. The point of the event horizon, where there's a theoretical infinitely thin space indicating it, is to show when the end of freedom, and the start of unwitting gravitational pull into the planet. The 2D representation isn't showing anything special, it's just showing where that point in space is.
You could do this for literally most things. Lets say I want to know where my fingertips end and the vacuum of space begins (Assume I'm in space). I would have a 2D representation of an infinitely thin position. Not because there's some 2D anything there, but because the concept you want to model only requires 2 dimensions.