Has Universe a "center" ?

N_Molson

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I've been absorbing documentaries and other data about cosmology for over 10 years, and now I'm stucked with a question, which AFAIK, might be the limit of our current knowledge about the Universe.

For a long time I was certain that the "Big Bang" was pretty much a big explosion. At first there was a "singularity" (pretty much an infinitely small geometrical point, no idea why or what went there, possibly something from another dimension) of near infinite density and energy, that "blew up" and created Space, Time, Weak Nuclear & Strong Nuclear fundamental forces that rule everything we can observe. I can understand that. Also the recent "Dark Matter / Dark Energy" discoveries show that, unlike what we could expect, the "bubble" of matter created by the Big Bang won't collapse after the initial momentum is depleted, but will continue to expand forever (as it seems that on a huge scale, "void" between objects pushes them further away more than Gravity can attract them). I can conceive that too, the Universe we know might end "spaghettified" by a slow but infinite acceleration. OK, fair enough.

But now comes the trouble.

1. Astrophysicists say that the Universe is like 13.7 billions years old. Beyond that is the "Planck Wall", which is a bit like an "inverted black hole event horizon" to me, and that is anyways quite close from the Big Bang "t0" instant.

2. Light speed is a constant, and everything we look at is actually "delayed". Even the Moon image we see in the sky is like 1 second old. And I don't take into account what happens between our retina and our brain vision, memory and "get everything together" centers, which takes some additional nanoseconds. So when we watch from the Earth the stars / galaxies / anything around us, it's pretty much a sailor with binoculars scanning the horizon. There's a limit beyond which he can't see. In the sailor case the cause is Earth curvature, in the star-watching case it's because there's nothing older than 13.7 billons light-years, and then it's like an horizon for us as speed of light is finite.

3. From there I would expect :

3a. That the "Big Bang" "explosion" detonated from a point in the Universe we would define as V_(0, 0, 0) relatively to the Universe in physics.

3b. That all the matter, antimatter, energy, anything released from there can't be further away from that V_(0, 0, 0) than a 13.7 billions light-years limit, which happens to be the speed of light (nothing can travel faster than the speed of light, remember ?).

4. There's a contradiction. Our radiotelescopes "see" or rather hear stuff in every direction, in a 13.7 billions light-years "bubble" around Earth.

5. We should be the center of the Universe. That's impossible. The mere fact people once believed Earth was the center of the Solar System is a proof to say that. And from what I can see in documentaries, most scientists say that the Universe is, as far as we know, infinite. So what's ? I am wrong assuming that the "Big Bang" happened at a V_(0, 0, 0) "point" and instead was something "global", infinite and undetermined in space (and time) ? This is a bit mind-blowing. If there are other "dimensions" from other "Big Bangs", might them simply be around on the same "plane", possibly intersecting with ours, but for now out of visual range (13.7 billions light-years) ?

Any help welcome. :facepalm: :hailprobe: :rofl:
 
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Loru

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3. From there I would expect :

3a. That the "Big Bang" "explosion" detonated from a point in the Universe we would define as V_(0, 0, 0) relatively to the Universe in physics.

3b. That all the matter, antimatter, energy, anything released from there can't be further away from that V_(0, 0, 0) than a 13.7 billions light-years limit, which happens to be the speed of light (nothing can travel faster than the speed of light, remember ?).

Space itself is not subject to lightspeed limit. As far as we know it it might be expanding much faster and "carry" farthest galaxies so they apparently move away faster than speed of light (their light got so redshifted it dissapears altogether similar to object at the event horizon)

We don't know total energy big bang had so while we have reasonable estimation of total energy in our visible bubble, we have have no idea how big entire universe is. Actually if it's big enough it might be even closed (3d surface of 4 dimensional sphere) and due to it's size we don't see curvature.
 

N_Molson

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Space itself is not subject to lightspeed limit.

Thanks, that really unlocks most of the issues I had. If initial expansion had no finite speed, indeed we can't know the size of the Universe. :thumbup:
 

jroly

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I did read an article explaining that people can not understand the big bang and the creation of the universe because everything we know and ever experienced is cause then effect. Obviously if nothing existed prior to the big bang, then there was first an effect and then everything followed cause then effect. So effect->cause->effect->cause->etc.

Everything must proceed something, but at the beginning something happened which did not proceed something.
 

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Well the bang created the universe by essentially expanding all space outwards for the aforementioned singularity, which rate is expanding for some reason. So you could say every spot in the universe is the location of the big bang's singularity. As far as we understand it anyway.
 

Linguofreak

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Thanks, that really unlocks most of the issues I had. If initial expansion had no finite speed, indeed we can't know the size of the Universe. :thumbup:

Also, the expansion doesn't really have a "speed" at all. It's more that in a given amount of time a given distance in space will grow by a certain amount. The primary factor in the cosmological redshift is not the recessional velocity of the galaxy that emitted the light, it's the photons being stretched to longer wavelengths as the space they travel through expands (indeed, the farthest galaxies are at redshifts that would correspond to velocities much faster than light if the redshift were indeed a Doppler shift due to recessional velocity).
 

Unstung

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I highly recommend watching these videos:
https://youtu.be/aPStj2ZuXug
https://youtu.be/JDmKLXVFJzk
https://www.youtube.com/playlist?list=PLsPUh22kYmNA6WUmOsEEi32zi_RdSUF4i

Space itself is not subject to lightspeed limit. As far as we know it it might be expanding much faster and "carry" farthest galaxies so they apparently move away faster than speed of light (their light got so redshifted it dissapears altogether similar to object at the event horizon)

The expansion has been calculated, one survey found it to be 74.2 ± 3.6 km/s/Mpc. More distant galaxies are receding faster. It turns out that the expansion of the universe is accelerating, caused by dark energy.
 
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n72.75

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The universe, as far as we can tell has 0 curvature which means it is infinite.

The universe has always been infinite; it's the density of "space" that's changing.

So every point in the universe appears to be the center to any observer. And the observable universe will appear to be approximately the same size to them.
 

Matias Saibene

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Space itself is not subject to lightspeed limit.

200 years later, and a Universe cheat...

latest


or worst better...

axiom_at_warp_speed_by_m_0cleanerdroid-d4lhrlz.png


remember use sunglasses.
:cheers:
 

Linguofreak

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The universe, as far as we can tell has 0 curvature which means it is infinite.

The universe has always been infinite; it's the density of "space" that's changing.

So every point in the universe appears to be the center to any observer. And the observable universe will appear to be approximately the same size to them.

Not strictly true: it could be a hypertorus, which would also have zero curvature and would be finite. But whatever the size if the universe, it is much larger than the observable universe.
 

Fizyk

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Not strictly true: it could be a hypertorus, which would also have zero curvature and would be finite.
What sometimes makes scientists dismiss the hypertorus possibility is that it would not be isotropic (you would have to travel further in some directions to go back to the starting point than in other ones). If we want to have flat, isotropic universe, AFAIK it has to be infinite, unfortunately.
 

Urwumpe

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What sometimes makes scientists dismiss the hypertorus possibility is that it would not be isotropic (you would have to travel further in some directions to go back to the starting point than in other ones). If we want to have flat, isotropic universe, AFAIK it has to be infinite, unfortunately.

Well, if it is a sufficiently large hypertorus, the differences would only be noticeable in larger scales, like galaxy clusters.
 

Fizyk

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Well, if it is a sufficiently large hypertorus, the differences would only be noticeable in larger scales, like galaxy clusters.
We do explore larger scales, for example via baryon acoustic oscillations, so my guess would be that effects caused by non-isotropicity (is that how you say it?...) would already be noticed if they were there. I'm not sure, though.
 

Urwumpe

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We do explore larger scales, for example via baryon acoustic oscillations, so my guess would be that effects caused by non-isotropicity (is that how you say it?...) would already be noticed if they were there. I'm not sure, though.

To make it clear, I am just pulling a leg here a bit: There is no hypertorus that can't be made so large, that its effect could not be hidden in the measurement errors of any observation. You just make it more infinity-like.

You could only be sure that the universe is NOT infinite, by measuring its limits, not the other way around by proving it is not limited by not finding a limit yet. (In the worst case, we could just be probing around from the limits all the time and thus be failing to see them)

Again, it is a bit of an attempt by a non-scientist to be scientifically funny, so don't get mad about me.

Though I must say: It would be really funny if everything we see in 13 billion light years distance is just our own place in the solar system from different perspectives...
 

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What sometimes makes scientists dismiss the hypertorus possibility is that it would not be isotropic (you would have to travel further in some directions to go back to the starting point than in other ones). If we want to have flat, isotropic universe, AFAIK it has to be infinite, unfortunately.

I think cosmic inflation solves the flatness problem without requiring an infinite universe.

Actually, I may be thinking of homogeneity rather than isotropy.
 
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N_Molson

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So, from what I read here, the answer to the answer to the original question is "Rather no" I guess. Just some like infinite fabric of Space/Time (yeah, rather a baloon)... :hmm:

But still... at some point, like a few nanoseconds after the initial Bang, the Universe had some kind of finiteness ? Well, back then it meant nothing, because Time and Space themselves were insanely "compressed" so to say, but could we say from our today's perspective something like "at t+0,000...0001 seconds, the Universe had merely the size of our Solar System, then a tiny interval later, it had the size of the Milky Way, etc... ?" :hmm: :hmm:

Or am I summing up potatoes and carrots, so to say ?
 

Urwumpe

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So, from what I read here, the answer to the answer to the original question is "Rather no" I guess. Just some like infinite fabric of Space/Time (yeah, rather a baloon)... :hmm:

But still... at some point, like a few nanoseconds after the initial Bang, the Universe had some kind of finiteness ? Well, back then it meant nothing, because Time and Space themselves were insanely "compressed" so to say, but could we say from our today's perspective something like "at t+0,000...0001 seconds, the Universe had merely the size of our Solar System, then a tiny interval later, it had the size of the Milky Way, etc... ?" :hmm: :hmm:

Or am I summing up potatoes and carrots, so to say ?

Well, remember: Everything expands the same way, so the Bang happened literally everywhere we know. Giving the universe some kind of size is pretty hard since we only know what we see and this view is likely just a small cross section of the whole universe.

If everything you know about space is within this universe, its hard to tell how large it is.
 

N_Molson

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Right, so I think what mislead me is some 3D animations showing a flashy point expanding into an energy ball that explodes in clouds of atoms. After all, a monitor only displays 3 dimensions (height, width + time), so it's an horrible tool to explain such an complex phenomenon. They have to take shortcuts. :hmm:
 

Linguofreak

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But still... at some point, like a few nanoseconds after the initial Bang, the Universe had some kind of finiteness ? Well, back then it meant nothing, because Time and Space themselves were insanely "compressed" so to say, but could we say from our today's perspective something like "at t+0,000...0001 seconds, the Universe had merely the size of our Solar System, then a tiny interval later, it had the size of the Milky Way, etc... ?" :hmm: :hmm:

When such things are said, they refer to the observable universe: the set of points in the universe for which it is possible for light from those points to have reached us since the big bang. The observable universe is, was, and always will be finite as the speed of light is finite and there has only been a finite amount of time since the big bang. We don't know how much else there is beyond that, though we have some clues that the universe as a whole, if finite, is at least immensely larger than the observable universe.
 
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