I know we’re in a meme community but this did get me thinking… Not only is the Earth spinning but it’s also in an orbit around the Sun which is also orbiting around the center of the Milky Way which is moving through space relative to other galaxies and so on.
Do we have enough information to calculate a position in space in the future for Earth without a fixed reference other than current point?
That’s what einstein said. There is no fixed reference frame, but only relative ones. Every “inertial”(meaning, motion without any external force) frame of reference is equally valid as any other inertial frame movibg with respect to it.
But for sure we can tell earth’s orbit is not inertial since circular motion occur, which is due to external force of gravity.
Shouldn’t it be (at least theoretically) possible to find some sort of geometric center where - on average - the rest of the universe is expanding away from?
That could sort of explain why it’s inherently impossible to determine the center - but that doesn’t rule out the existence of a geometric center of the universe, right?
Kiiiind of. I suppose we haven’t definitively ruled out a geometric centre, but it runs up against Occam’s Razor in a really big way. A centre of the universe would require some kind of boundary or edge to the universe, and the physical dynamics of how that would even work are very much non-trivial.
Generally the universe is thought to either loop back on itself like the surface of a globe, or extend infinitely in every direction.
I’m not sure if I follow the balloon analogy. Sure, you can’t find the center on it’s surface. But somewhere within the balloon, there is a center. It might be virtually impossible to determine the center while actively inflating the balloon, but that doesn’t mean there isn’t any center? What makes the rest of the universe fundamentally different from an inflating balloon?
I’m genuinely curious.
With the balloon analogy it’s not about the center of the volume, we ignore the volume and assume that the surface is a 2d universe. That’s what’s impossible to find the center of. I don’t really like that analogy though personally so I’m not going to discuss that one further.
Just think about it this way: the observable universe can only be so big (because when the expansion between two distant enough objects is faster than the speed of light/causality, they no longer have a means of interacting). We don’t observe any sort of obvious boundary to the universe within our visible portion that we might be able to assume a center based on. So it’s not that we know that there isn’t a center (afaik, someone correct me if I’m wrong), it’s that it’s likely impossible know that there is, let alone find it from our position in the universe. So, we might as well assume that it’s all relative.
Imagine you woke up on a raft in the middle of the ocean on an alien planet. It’s foggy, you can’t see stars, you can’t see any landmarks at all. There are other things floating in the water too though. There might be a geometric center to that ocean, but you can’t see it, and you have no other hint at where it is. For all you know, the entire planet is ocean and there’s is no center to find. This is sort of the situation we Earthling are in now, except that at least the the rafter can drift and perhaps eventually find and map out a coast. Because our space-time is expanding, our observable universe will never be bigger than it is now.
OK, so what we discovered was that if we look far into the universe, all stuff is moving away from us (we can measure that using the famous red shift). Additionally, the farther something is, the faster it is moving away from us.
Now the simplest explanation would be that the Earth just happens to be exactly in the middle of this expansion. However, it is much more reasonable to assume our location in the universe is not special in any way and that you’d see things moving away from you if you did these measurements anywhere else. If that is so, the universe is expanding, everywhere. There’s more space in the universe every second and there’s still the same amout of matter, hence it is becoming larger, emptier and colder.
The next step is to look back and think of how the universe looked in the past. Since it’s getting bigger and bigger, it must have been smaller before and if you go back in time enough you’ll find a tiny universe that still has the same total amount of matter in it, just densely packed into possibly just a single point. Hard to say what preceded that moment, but we can predict a universe which started as an incredibly energetic singularity which exploded out and has been growing ever since. We call that moment the Big Bang and if anything, that is the centre from which everything is expanding. Not found somewhere in space but in time.
Back to the balloon analogy, the centre would be the deflated little thing you start with. Maybe a better analogy would be the little clump of molten glass at the end of a glassblower’s pipe. He begins to blow, the big bang happens, expansion starts. Fast forward 13.7 billion years (which happens to be today) - the glass has expanded into a large spherical object and there’s some tiny people living on it.
They only live on the surface of the glass and the sphere is so huge (or they are so tiny) that they can’t even tell that their world is spherical. They measure distances to some other specs littered across the glass and find that they are all moving away from them, faster the farther they are. Their universe is expanding, but where is the centre of expansion? They cannot point to it, because they only live in two dimensions, fully defined by the sufrace of the sphere. But if they could point in a direction perpendicular to all the spacial dimensions they know, they could point to the point where the sphere started, long in their past.
So the right question is not form “where” the universe expands but “whence”. The Big Bang. The very start. Somewhere far in time, which is just another direction, perpendicular to up, left, forward.
I very much appreciate the effort to write your repsonse, and if you’re out of time or energy I completely understand.
So if I’m understanding you right, we’re 3-dimensional creatures living in a 4-dimensional universe, with the 4th dimension being… time? And time behaves completely different from the other 3 dimensions, which is why we can’t just disregard or freeze it when trying to determine a center?
It’s a bit more complicated than that. One of the consequences of theory of relativity was the realisation that time and space cannot be separated and it only make sense to speak of “spacetime”, a four-dimensional continuum rather than just three as we thought until that point. As far as I understand it, time is not really different from the other dimensions, it just seems that way to us.
I heard an explanation that has to do with entropy - the total amount of entropy is always increasing (I’m not going to even try to explain this since I only barely understand that myself) and the act of encoding information (whether we’re talking a brain forming a new memory, a computer storing some data, or me writing this comment) is a process that always increases entropy, therefore any kind of memories can only be of things in the past rather than the future, and so every moment of our lives feels like “now”, the boundary between the written and the unwritten. I don’t think we’re actually moving in time. It’s just an illusion.
That said, while my earlier explanation is simplified and probably contains a ton of inaccuracies, I’m fairly confident it’s accurate in broad strokes. This comment though, I’m not nearly as confident this is the current scientific consensus. Just what makes sense to me, so take it with a grain of salt.
If you’re interested in stuff like this, I cannot recommend The Elegant Universe by Brian Greene enough. Unlike me he’s someone who actually knows exactly what he’s talking about and he explains everything much better than I ever could.
We also get a few glances of the coordinate system that the time machines use in doctor who. It appears to have enough digits for a date/time as well as an X/Y/Z grid coordinate.
I don’t think we have a relative fixed point to go off unless you choose the centre of the big bang. It’s all relative to other things around us which are also moving lol
I know we’re in a meme community but this did get me thinking… Not only is the Earth spinning but it’s also in an orbit around the Sun which is also orbiting around the center of the Milky Way which is moving through space relative to other galaxies and so on.
Do we have enough information to calculate a position in space in the future for Earth without a fixed reference other than current point?
That’s what einstein said. There is no fixed reference frame, but only relative ones. Every “inertial”(meaning, motion without any external force) frame of reference is equally valid as any other inertial frame movibg with respect to it.
But for sure we can tell earth’s orbit is not inertial since circular motion occur, which is due to external force of gravity.
Edit:typo
Shouldn’t it be (at least theoretically) possible to find some sort of geometric center where - on average - the rest of the universe is expanding away from?
Turns out, no; every point is expanding away from every other point, so every point sees itself as the center of expansion.
That could sort of explain why it’s inherently impossible to determine the center - but that doesn’t rule out the existence of a geometric center of the universe, right?
Kiiiind of. I suppose we haven’t definitively ruled out a geometric centre, but it runs up against Occam’s Razor in a really big way. A centre of the universe would require some kind of boundary or edge to the universe, and the physical dynamics of how that would even work are very much non-trivial.
Generally the universe is thought to either loop back on itself like the surface of a globe, or extend infinitely in every direction.
For a geometric center you would need a boundary of the universe
No, for the same reason you can’t find a point a balloon is expanding from on its surface. Everything is expanding everywhere.
I’m not sure if I follow the balloon analogy. Sure, you can’t find the center on it’s surface. But somewhere within the balloon, there is a center. It might be virtually impossible to determine the center while actively inflating the balloon, but that doesn’t mean there isn’t any center? What makes the rest of the universe fundamentally different from an inflating balloon? I’m genuinely curious.
With the balloon analogy it’s not about the center of the volume, we ignore the volume and assume that the surface is a 2d universe. That’s what’s impossible to find the center of. I don’t really like that analogy though personally so I’m not going to discuss that one further.
Just think about it this way: the observable universe can only be so big (because when the expansion between two distant enough objects is faster than the speed of light/causality, they no longer have a means of interacting). We don’t observe any sort of obvious boundary to the universe within our visible portion that we might be able to assume a center based on. So it’s not that we know that there isn’t a center (afaik, someone correct me if I’m wrong), it’s that it’s likely impossible know that there is, let alone find it from our position in the universe. So, we might as well assume that it’s all relative.
Imagine you woke up on a raft in the middle of the ocean on an alien planet. It’s foggy, you can’t see stars, you can’t see any landmarks at all. There are other things floating in the water too though. There might be a geometric center to that ocean, but you can’t see it, and you have no other hint at where it is. For all you know, the entire planet is ocean and there’s is no center to find. This is sort of the situation we Earthling are in now, except that at least the the rafter can drift and perhaps eventually find and map out a coast. Because our space-time is expanding, our observable universe will never be bigger than it is now.
OK, so what we discovered was that if we look far into the universe, all stuff is moving away from us (we can measure that using the famous red shift). Additionally, the farther something is, the faster it is moving away from us.
Now the simplest explanation would be that the Earth just happens to be exactly in the middle of this expansion. However, it is much more reasonable to assume our location in the universe is not special in any way and that you’d see things moving away from you if you did these measurements anywhere else. If that is so, the universe is expanding, everywhere. There’s more space in the universe every second and there’s still the same amout of matter, hence it is becoming larger, emptier and colder.
The next step is to look back and think of how the universe looked in the past. Since it’s getting bigger and bigger, it must have been smaller before and if you go back in time enough you’ll find a tiny universe that still has the same total amount of matter in it, just densely packed into possibly just a single point. Hard to say what preceded that moment, but we can predict a universe which started as an incredibly energetic singularity which exploded out and has been growing ever since. We call that moment the Big Bang and if anything, that is the centre from which everything is expanding. Not found somewhere in space but in time.
Back to the balloon analogy, the centre would be the deflated little thing you start with. Maybe a better analogy would be the little clump of molten glass at the end of a glassblower’s pipe. He begins to blow, the big bang happens, expansion starts. Fast forward 13.7 billion years (which happens to be today) - the glass has expanded into a large spherical object and there’s some tiny people living on it.
They only live on the surface of the glass and the sphere is so huge (or they are so tiny) that they can’t even tell that their world is spherical. They measure distances to some other specs littered across the glass and find that they are all moving away from them, faster the farther they are. Their universe is expanding, but where is the centre of expansion? They cannot point to it, because they only live in two dimensions, fully defined by the sufrace of the sphere. But if they could point in a direction perpendicular to all the spacial dimensions they know, they could point to the point where the sphere started, long in their past.
So the right question is not form “where” the universe expands but “whence”. The Big Bang. The very start. Somewhere far in time, which is just another direction, perpendicular to up, left, forward.
I very much appreciate the effort to write your repsonse, and if you’re out of time or energy I completely understand.
So if I’m understanding you right, we’re 3-dimensional creatures living in a 4-dimensional universe, with the 4th dimension being… time? And time behaves completely different from the other 3 dimensions, which is why we can’t just disregard or freeze it when trying to determine a center?
It’s a bit more complicated than that. One of the consequences of theory of relativity was the realisation that time and space cannot be separated and it only make sense to speak of “spacetime”, a four-dimensional continuum rather than just three as we thought until that point. As far as I understand it, time is not really different from the other dimensions, it just seems that way to us.
I heard an explanation that has to do with entropy - the total amount of entropy is always increasing (I’m not going to even try to explain this since I only barely understand that myself) and the act of encoding information (whether we’re talking a brain forming a new memory, a computer storing some data, or me writing this comment) is a process that always increases entropy, therefore any kind of memories can only be of things in the past rather than the future, and so every moment of our lives feels like “now”, the boundary between the written and the unwritten. I don’t think we’re actually moving in time. It’s just an illusion.
That said, while my earlier explanation is simplified and probably contains a ton of inaccuracies, I’m fairly confident it’s accurate in broad strokes. This comment though, I’m not nearly as confident this is the current scientific consensus. Just what makes sense to me, so take it with a grain of salt.
If you’re interested in stuff like this, I cannot recommend The Elegant Universe by Brian Greene enough. Unlike me he’s someone who actually knows exactly what he’s talking about and he explains everything much better than I ever could.
It’s not, because the space itself is expanding
There is not central point in the universe, and no way to calculate a position. Everything is relatove
Here, that might be interesting to you.
You are not where you think you are
This is why Doctor Who has a time and space machine. Also because the BBC didn’t have the effects budget to show him flying around.
We also get a few glances of the coordinate system that the time machines use in doctor who. It appears to have enough digits for a date/time as well as an X/Y/Z grid coordinate.
I don’t think we have a relative fixed point to go off unless you choose the centre of the big bang. It’s all relative to other things around us which are also moving lol
There actually isn’t a center of the big bang, every point is expanding away equally.
Isn’t everywhere kinda the center?
Effectively, yes
I think you’ll run into the three body problem.