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"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."
We're currently unaware of any fixed coordinate system for space itself. There may be one, we have no basis of reference for it.
Ah, but using the cosmic microwave background we actually can determine a universal coordinate system to fix a point in space.
cosmic microwave
Oh, so that's why Earth is spinning!
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.
Yeah, and some asshole thought it'd be cool to put fish in it.
that sounds like you're relating your position to something else 😏
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.
I think they mean it would be "Stay at this exact point in the CMB rest frame" but not "in space" because the "space rest frame" is nonexistent
That’s a little wordy though, so most people would just say “in space”
Why cosmic microwave background radiation? Is that any less arbitrary than e.g. the sun?
i mean if we were to communicate with aliens in another galaxy it would be the "least arbitrary" one
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?
I'm at the place where the CMBR is evenly redshifted in all directions.
that's not a place that's a frame of motion (i think)
the only issue is it's hard to define an origin for that frame, so yeah it's not gonna be all that useful indeed
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
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.
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?
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.
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
I've given up trying to explain it to people as an explosion. Media and innate biases make people view that word as a "kaboom" and form a mental picture.
I tell people that the universe was likely always infinite. In the beginning it was infinitely dense and essentially a singularity, but that singularity wasn't a point in space like a black hole, it was a everything and everywhere. The universe was ultra dense, infinite energy, then all at once, the whole thing got bigger like the infinite hotel paradox, an infinite space can get bigger. So all the whole infinite space just stretched out in all directions, making space open up and the energy less dense.
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.That's absolutely right; there's no special origin point in space where the Big Bang began. However, there is a specific reference frame that the Big Bang occured in, which we can measure by looking at the redshift of the cosmic microwave background left over from it. The solar system is currently moving at around 600km/s relative to that.
Interestingly, this is actually an expanding reference frame due to the universe's expansion, so two observers locally at rest relative to it will each see the other moving away.
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!
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.
So from wherever you look, the universe is expanding away from you (I.e., other things in it move away from you).
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.
So from wherever you look, the universe is expanding away from you
Therefore, you can see that the universe doesn’t have a centre.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
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.
The big bang created the universe within space.
This is not the accepted model, it wouldn't work with our current observations. There was no "outside" space before space started expanding. When the universe was smaller, it was also infinite but an infinitely dense medium with nothing outside of it. The whole universe was infinitely dense energy, there was no "outside" or "inside" to speak of, even the geometry of spacetime was infinitely distorted, so there was no "before" or "after" states for literally anything.
Time and space didn't begin until the expansion event. At that point, if it were possible to be an observer, it would seem like suddenly everything stretched away in all directions from all points, and this allowed interactions and events to start occuring, which we mark as the passage of time.
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.
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.
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