"but Stephen, there are no fixed points in space. Space is relative, meaning you can only define positions relative to other things. You demand the fundamentally physically impossible of me, Stephen."
In the sense that the Cosmic Microwave Background (CMB) is visible from every point in space. No matter where you are you can determine your position relative to the CMB, making it a common reference point for the entire universe.
I understand that it is visible from all of space, but doesn't it look the same from all points in space? Wouldn't everyone looking at it simply conclude "I am at the center of the CMB"? How would you use it to specify a certain point?
Apparently it is just the slightest bit warmer on one side. It's called the dipole of the cmb. I don't fully understand it, but as far as I know astrophysicists don't understand it either. ;-)
But how would you use the dipole to specify where you are? Isn't the dipole the same everywhere? I'd think the dipole could possibly specify a fixed direction, but that's hardly enough to specify a fixed point referencing only the CMB.
Because a while back some people thought that the background radiation was polar or bipolar from which we could infer a center of the known universe resulting from the big bag, however that has since been disproven by comparing different measurements with inconsistent results. There is no direction in cosmic background radiation.
Because it's the leftover heat from the big bang, now just stretched so far it's become static background radiation, but it's always been there — unlike our sun.
Is it tho? Assuming there was a big bang, isnt it fair to call that origin point 0 0 0 in 3D space? Subjective space is relative, but that doesnt mean space itself is relative.
that's not how the big bang works, the whole thing about the big bang is that it was a singularity containing all of space in a single point.
The standard analog is to take a small balloon with dots painted on it, then inflating it. The surface of the balloon is spacetime, and as it shows there is no origin, everything just gets more distant from everything else.
They are only talking about the surface of the balloon. For the purpose of the metaphor only the surface exists. Imagine infinite space. Now imagine we divide infinite space into a grid of 1 meter cubes. Now imagine we double the size of every cube. That's more or less how expansion works, it is an expansion of space everywhere, not outwards like an explosion.
the big bang wasn't an explosion from a point, it was an explosion of a point in space. That one point is still expanding to this day. Everything is moving away from everything else, which wouldn't be the case in an "ordinary" explosion. We are all still in that one point, it's just that that point has expanded. The center of the universe is, in the literal sense of the word "literally", everywhere.
Im kinda trollin at this point, but in an ordinary explosion, in a vacuum without external gravity, everything would indeed have a different initial velocity and direction, so everything would be moving away from everything else.
imagine standing at the side of the explosion looking towards it. some debris will be blown way from you, but some will be coming towards you. You are something, and not everything is moving away from you, some debris hits you in the face. That's an explosion in space.
An explosion of space is defferent. Everything will be moving away from you, regardless of where you are or which side you're facing.
Something wasn't in space and it exploded. Space itself exploded. your argument only holds if you are exactly in the explosion source.
So from wherever you look, the universe is expanding away from you (I.e., other things in it move away from you).
Therefore, you can see that the universe doesn't have a centre. From this and some other a bit more complicated things, one can see that the Big Bang never had a single point but rather expanded everywhere at once when it happend. Although often called expansion from one point that is wrong.
Also technically you would need to give a time dimension as we live in 4D space.
the 0 0 0 0 (spacetime) orientation system would be possible if the universe was a minkowski space and thus flat, but spacetime is curvy due to relativistic effects, which prevents any sort of flat orientation like that
I'm just going to jump on the bandwagon and helpfully say; think of the universe as a large expanding paper bag.
Initially it was flat, but then the bagger expanded it in the third dimension and put bananas in it. Imagine now that you are one of those bananas, but oh no, here comes the 2L Pepsi bottle ready to crush us. Thankfully the bagger takes us out of the bag first, puts the cola bottle in, and then puts us back in on top.
Think of an expanding balloon as the universe, and the paperbag as the expanding multiverse. Now assuming a uniform conservative rate of 1.5 marvel movies a year, how much does the paper bag fill with vomit before the balloon bursts?
Yeah, I believe it was Einstein who showed that space and time are linked together and cannot be separated, although I won't claim to understand that concept.
Proper time is only defined along a timelike world line, e.g. the timeline of a specific reference point / object. It's "objective" in the sense that is true for the reference point, but other reference points may (for example) perceive distant events in a different order
If the speed of light has a max speed, can't we just measure it in all directions to find out exactly how we are moving and therefore get a absolute zero speed?
The earth is rotating, which is a non-inertial reference frame. Fido simply uses its own reference frame, which following the command is now inertial. The result is that Fido is no longer affected by gravity, and slowly floats away just as in the comic
Also, it's a little inaccurate as the dog would be moving at hundreds of thousands of kilometers per hour, either burning up in the Earth's atmosphere or plowing through its surface. Also, I don't think dogs have the ability to do this, so there's that.
because fixed points in space (stationary reference frames) fall inwards into gravity wells as time progresses, Fido, would need to burrow into the center of the earth. Fido should shoot into space like that if told to stay at a fixed point relative to the cosmic microwave background
That dog is suddenly spinning very fast. Breaking physics so hard time doesn't matter. He'll be back on Earth in front of his owner several times before the owner will have had time to react.
"but Stephen, there are no fixed points in space. Space is relative, meaning you can only define positions relative to other things. You demand the fundamentally physically impossible of me, Stephen."
Ah, but using the cosmic microwave background we actually can determine a universal coordinate system to fix a point in space.
Oh, so that's why Earth is spinning!
Yeah, and some asshole thought it'd be cool to put fish in it.
The centre is hot while the outside is cold - that's how we know it's true
Life is naught but a warm burrito on the rotating microwave plate of Earth.
But only related to the cosmic microwave background, which, while more universal than most other reference frames, is ultimately still arbitrary
North is arbitrary as well, that doesn't mean you can't use it for spatial referencing.
Yes, for practical purposes, absolutely! But you're always just aligning with something else moving through space, not space itself
It can be as arbitrary as it wants it still allows you to use relative positioning to determine a fixed point.
That’s a little wordy though, so most people would just say “in space”
that sounds like you're relating your position to something else 😏
Why cosmic microwave background radiation? Is that any less arbitrary than e.g. the sun?
Wouldn't the conversations go like this?
Me: I'm about 2/3rds out the longest arm of my galaxy
Alien: OK
vs
Me: I'm at the place where the CMBR is evenly redshifted in all directions.
Alien: Huh, me too?
Well, it's the only thing we know of that can be used in the whole universe.
Use it how? I've never heard about this, and I can't seem to find anything about it by searching
In the sense that the Cosmic Microwave Background (CMB) is visible from every point in space. No matter where you are you can determine your position relative to the CMB, making it a common reference point for the entire universe.
I understand that it is visible from all of space, but doesn't it look the same from all points in space? Wouldn't everyone looking at it simply conclude "I am at the center of the CMB"? How would you use it to specify a certain point?
Apparently it is just the slightest bit warmer on one side. It's called the dipole of the cmb. I don't fully understand it, but as far as I know astrophysicists don't understand it either. ;-)
But how would you use the dipole to specify where you are? Isn't the dipole the same everywhere? I'd think the dipole could possibly specify a fixed direction, but that's hardly enough to specify a fixed point referencing only the CMB.
Huh, you're right. I guess at a position you can use it to define a point. A point where you don't move in any other direction.
Because a while back some people thought that the background radiation was polar or bipolar from which we could infer a center of the known universe resulting from the big bag, however that has since been disproven by comparing different measurements with inconsistent results. There is no direction in cosmic background radiation.
Because it's the leftover heat from the big bang, now just stretched so far it's become static background radiation, but it's always been there — unlike our sun.
Sure, but it is also expanding equally at all points same as the universe, so how do we define a fixed point in relation to it?
But bjoern tantau said we could - is he wrong?
Is it tho? Assuming there was a big bang, isnt it fair to call that origin point 0 0 0 in 3D space? Subjective space is relative, but that doesnt mean space itself is relative.
that's not how the big bang works, the whole thing about the big bang is that it was a singularity containing all of space in a single point.
The standard analog is to take a small balloon with dots painted on it, then inflating it. The surface of the balloon is spacetime, and as it shows there is no origin, everything just gets more distant from everything else.
Doesn't the balloon have a centre of mass that we can adjust coordinates to.... all the time.... at millions of km per second.
Okay, I see your point.
They are only talking about the surface of the balloon. For the purpose of the metaphor only the surface exists. Imagine infinite space. Now imagine we divide infinite space into a grid of 1 meter cubes. Now imagine we double the size of every cube. That's more or less how expansion works, it is an expansion of space everywhere, not outwards like an explosion.
I've been struggling to not see it as explosion/outward expansion. This really helped!
the big bang wasn't an explosion from a point, it was an explosion of a point in space. That one point is still expanding to this day. Everything is moving away from everything else, which wouldn't be the case in an "ordinary" explosion. We are all still in that one point, it's just that that point has expanded. The center of the universe is, in the literal sense of the word "literally", everywhere.
Like one of those pills you put in water and it turns into a sponge TRex!
Based and T-Rexpilled.
I am the center of the universe. Got it.
Wait until you hear about quantum immortality...
Being the center of the universe, I already assumed I was immortal.
Objectively based solipsism
Im kinda trollin at this point, but in an ordinary explosion, in a vacuum without external gravity, everything would indeed have a different initial velocity and direction, so everything would be moving away from everything else.
imagine standing at the side of the explosion looking towards it. some debris will be blown way from you, but some will be coming towards you. You are something, and not everything is moving away from you, some debris hits you in the face. That's an explosion in space.
An explosion of space is defferent. Everything will be moving away from you, regardless of where you are or which side you're facing.
Something wasn't in space and it exploded. Space itself exploded. your argument only holds if you are exactly in the explosion source.
In space, we're still inside the explosion
So from wherever you look, the universe is expanding away from you (I.e., other things in it move away from you).
Therefore, you can see that the universe doesn't have a centre. From this and some other a bit more complicated things, one can see that the Big Bang never had a single point but rather expanded everywhere at once when it happend. Although often called expansion from one point that is wrong.
Also technically you would need to give a time dimension as we live in 4D space.
Wouldn't that be the case even with a center?
Yes indeed, you could see every point as the universe as its centre (or none of them).
When everything is center, nothing is.
No. The only logical explanation is that I am the center of the universe!
the 0 0 0 0 (spacetime) orientation system would be possible if the universe was a minkowski space and thus flat, but spacetime is curvy due to relativistic effects, which prevents any sort of flat orientation like that
I'm so glad you asked that.
Never had that many comments in my inbox
Think of a balloon expanding. All the dots on the surface are moving away from one another. No dot is the centre.
If they are all moving away from each other, that means if you reverse time they will all converge at a single point, which would be the center.
Every point is that point. Every point would see the whole universe converge on them simultaneously.
I'm just going to jump on the bandwagon and helpfully say; think of the universe as a large expanding paper bag.
Initially it was flat, but then the bagger expanded it in the third dimension and put bananas in it. Imagine now that you are one of those bananas, but oh no, here comes the 2L Pepsi bottle ready to crush us. Thankfully the bagger takes us out of the bag first, puts the cola bottle in, and then puts us back in on top.
And that's why I believe in God
Uh what?
Think of an expanding balloon as the universe, and the paperbag as the expanding multiverse. Now assuming a uniform conservative rate of 1.5 marvel movies a year, how much does the paper bag fill with vomit before the balloon bursts?
27 ducks?
The big bang created the universe within space. Space is literally, just space, an endless empty (as far as we know) vacuum.
No the big bang also created space time. The bang is the bang of space going from a point to infinite 3d space + time.
Yeah, I believe it was Einstein who showed that space and time are linked together and cannot be separated, although I won't claim to understand that concept.
We're currently unaware of any fixed coordinate system for space itself. There may be one, we have no basis of reference for it.
Out of my depth here, but it seems that objective timespace coordinates can be determined while still meshing with relativity.
I'll just leave this here so someone else can explain why I'm wrong:
https://en.m.wikipedia.org/wiki/Proper_time
I know 4D spacetime can be non-euclidean, but I believe those are localized to areas experiencing relativistic extrema.
Proper time is only defined along a timelike world line, e.g. the timeline of a specific reference point / object. It's "objective" in the sense that is true for the reference point, but other reference points may (for example) perceive distant events in a different order
If the speed of light has a max speed, can't we just measure it in all directions to find out exactly how we are moving and therefore get a absolute zero speed?
Pfft! I read about it on a box of cereal 5 minutes ago and think I've come to some novel conclusions.
I had to switch from existential-os. That box was making me sad.
The earth is rotating, which is a non-inertial reference frame. Fido simply uses its own reference frame, which following the command is now inertial. The result is that Fido is no longer affected by gravity, and slowly floats away just as in the comic
This makes me sad.
Also, it's a little inaccurate as the dog would be moving at hundreds of thousands of kilometers per hour, either burning up in the Earth's atmosphere or plowing through its surface. Also, I don't think dogs have the ability to do this, so there's that.
We have never truly tested the limits of dogs. Only the limits of what THEY think we want.
What they want is to be with us, thus they would never use such a power even if they had it.
Good boy. Maybe too good.
because fixed points in space (stationary reference frames) fall inwards into gravity wells as time progresses, Fido, would need to burrow into the center of the earth. Fido should shoot into space like that if told to stay at a fixed point relative to the cosmic microwave background
Which frame of reference though? Also time is a dimension should the dog also freeze in time?
Altitude, latitude, longitude.
Not from Earth, but Sagittarius A*
That dog is suddenly spinning very fast. Breaking physics so hard time doesn't matter. He'll be back on Earth in front of his owner several times before the owner will have had time to react.
I KNEW YOU THOUGHT I WAS GOOD DOG!!!
Does anyone know the artist?
General relativity is for nerds (this is a joke).
I want to see the one where he bores a hole though the center of the earth.
Gooboi!!
Good one!