Why is the observable universe a sphere with us at the center?
In theory wouldn't that mean light(photons) is coming towards us from all directions? Pic related
Because we can see (roughly) the same distance in every direction
so it defines a sphere centered at where we observe from (here)
and yes, that does mean light's coming at us from every direction, but that's nothing particularly dazzling
if you look around you in space there's always going to be stars on all sides of you unless you were at the very edge of the universe for some reason
But how could it be coming from all directions. The singularity had to be at one point in one direction. That's like a grenade going off in front of you and feeling the shrapnel hitting your back
Think of the singularity as the entire observable universe. As the big bang occurs, the singularity expands on all sides, shooting light off in every direction. It's theorized that the universe may be expanding faster than the speed of light. If this is true, the observable universe will always be a sphere to us, as the things casting that light beyond that will be too far to see. The actual shape may be a cone, but we can only see a tiny bubble inside of said cone.
Is the fact that we are roughly in the middle of the observable universe "just a coincidence"? By that I mean: Would it be possible that in a hypothetical universe with the exact same properties as the one we inhabit now, we could only observe 1 m in some arbitrary direction, making it appear as though we were on the edge of the inside of a sphere?
That wasn't a satisfactory explanation for me, nor did my question pertain to the expansion of the universe.
Let me rephrase my question: If you by some magical contrivance were able to teleport to wherever you wanted within the universe, would the edges of the observable universe be equidistant and equal (e.g. 5 m in all directions from the sun and 5 m in all directions from earth) in all directions no matter where you were?
Because it's what you observe. Every observer has his own Observable Universe as a sphere (since the light is coming from all directions) with him at the center, it just happens that all the known observers are at Earth.
Various cosmological horizons.
Alright, I think I understand why nobody understands my question now. It's probably dumb anyway, but whatever:
As far as my limited understanding of astrophysics goes, the remnant electromagnetic radiation from the big bang is mainly in the microwave part of the spectrum, meaning that e.g. any visible light we can observe must've been emitted by some system of classical particles (e.g. a star).
Is it possible to (theoretically) position yourself in such a way that visible light from systems of classical particles (e.g. stars) is further away from you in arbitrary direction than it is in another arbitrary direction?
>Is it possible to (theoretically) position yourself in such a way that visible light from systems of classical particles (e.g. stars) is further away from you in arbitrary direction than it is in another arbitrary direction?
Don't know man. Would be dope as fuck though, I'll give you that
It doesn't have to end, there just has to be some area void of classical particles emitting visible light. With that, I read into your post that it would be theoretically possible, not that we will ever empirically find out.
Also, if you see maps of the cosmic microwave background (CMB), they will appear oval (pic related). I am assuming that this map is from earth's point of view in all directions, and that it is oval due to projecting a 3D visual onto a 2D plane (the picture). Is this assumption correct?
No, the big bang is not a local event it is background cosmology. If you take the modern idea of the big bang the universe was infinite at the start of inflation. That is the modern concept of the big bang, it lacks the idea of a singularity because we simply don't know. If you take the classical big bang singularity then the universe is infinite at any time after t=0. At the singularity itself it is not because all space would be coincident.
Is it also true that this observable light from stars etc is moving away from us in all directions? I recall reading that somewhere and it was hard to envision how that would be given the big bang.
The universe is expanding at the speed of light but not equivalently in all directions. Also, in case some might misunderstand, it isn't the edges of the universe that are expanding, it is the entirety of the universe itself.
The universe won't always look like a sphere. Let's say relative to us, if the space between us and the celestial objects in the upper regions of the observable universe expands faster than the speed of light, then we won't see that part of the observable universe, and it will look like a deformed sphere.
>if the space between us and the celestial objects in the upper regions of the observable universe expands faster than the speed of light, then we won't see that part of the observable universe
No. Many objects have recession velocities much higher than the speed of light. No new information can reach us from them but we can still see them because of the light in transit.
Also there is no evidence for inhomogenous expansion so it is a sphere.
>If the universe is expanding faster than the speed of light, how fucked are we?
Space is expanding uniformly, the farther apart you are the faster you are moving away from each other.
Local gravity also overpowers expansion, so the galaxies near us are not going anywhere (in fact we will collide with Andromeda in 4 billion years).
>No new information can reach us from them
That's the thing, in due time, those objects will go dark forever. When that happens, the spherical shape of the observable universe will change drastically.
Granted, this might take millions, if not billions of years to occur, but it will happen. Also, while there's no direct empirical evidence of inherent homogeneous expansion, the existence of dark energy certainly does it so that some regions of the universe will expand faster than others, so you're wrong there pal.
>That's the thing, in due time, those objects will go dark forever. When that happens, the spherical shape of the observable universe will change drastically.
How? Stop talking out of your ass.
Because the distance between us and those galaxies is fucking enormous. So as our gravitational interaction gets weaker and weaker with distance, the space in between is itself expanding at an increasing rate, and the expansion wins. The space between us and neighboring galaxies, however, is a lot smaller so gravity handily overpowers the expansion and causes them to drift toward us
What do you mean how? Just as stated earlier in this thread, the reason the observable universe is a sphere is because we see light from every direction in the universe, which makes it a sphere.
Now due to the expansion of the universe, there will be a point where light wont be able to overcome the expanding spacetime, and will never manage to reach Earth. Thus X celestial object emitting this light will completely darken out to our observatories. Once we see that a certain region of the sphere is completely dark compared to the rest, then that region of the sphere won't be considered a region of the "observable" universe anymore, and the real observable universe would change in shape to account for this.
There's an infinite, or at least way larger universe out there that we exclude from our observable universe model only because light from that part of the universe doesn't reach us. You'll see that due to the expansion of space, I don't know precisely, maybe in billions or trillions of years, assuming we still exist, our particle horizon will shrink considerably. Our observable universe will go from it is now, to being smaller, to even reaching our galaxy. Long in the future, our observable universe will only be our galaxy! And after that, it will only be our solar system!
This is why it won't remain a sphere forever.
Seriously? They go dark because eventually the expansion of distance between us and those galaxies becomes fast enough such that distance is being "created" faster than the photon can traverse that distance. It'd be like if you tried to run a mile but after you ran a half mile then suddenly it's two miles instead of one, meaning you have 1.5 miles left, and then after you ran another half mile suddenly there's 4 miles, so you have 3 left now. You'll never reach the end
>That's the thing, in due time, those objects will go dark forever.
They'll just fade forever, moving to higher redshift. Only because of the quantised nature of light will they ever truly go dark.
>When that happens, the spherical shape of the observable universe will change drastically.
No. That simply doesn't follow.
>the existence of dark energy certainly does it so that some regions of the universe will expand faster than other
No again. Dark energy is also not observed to be spatially inhomogeneous. No deviation from Lambda has been observed, it's called the cosmological Constant for a reason.
>Now due to the expansion of the universe, there will be a point where light wont be able to overcome the expanding spacetime, and will never manage to reach Earth. Thus X celestial object emitting this light will completely darken out to our observatories.
Yes, and this all happens uniformly across the observable horizon, which is a sphere.
>Once we see that a certain region of the sphere is completely dark compared to the rest, then that region of the sphere won't be considered a region of the "observable" universe anymore, and the real observable universe would change in shape to account for this.
Are you seriously this stupid? It's not like the observable horizon is drawn with a crayon around things we can see. It contains plenty of empty "dark space", because it's about what's possible to observe in principle, not in practice. It's a purely theoretical horizon. Not to mention that because the universe is isotropic, what you're describing can't happen.
So please, stop making shit up and just pick up a textbook. No one is impressed by your lies.
Yes, but not when they recede faster than the speed of light as was claimed.
>Once we see that a certain region of the sphere is completely dark compared to the rest
Expansion is purely a function of distance at these scales. If one part of the sky went dark it would across the entire sky at the same redshift.
In reality the observable universe is not defined by the furthest object we can see. You're misusing nomenclature here. It is derived from cosmological parameters. In standard cosmology it will always be spherical. It doesn't matter if it was just the solar system inside.
It's just as OP's picture shows, yeah, it's not simply a drawn line around what we see, but what we're supposed to see. Our telescopes and observatories are getting better, and we're start to see more distant objects, does that mean our observable universe grows? No, that's not my point.
It's in the fucking name for Christ's sake, OBSERVABLE universe. If there's something we're sure we can't observe due to the expansion of space, then that place isn't part of the observable universe anymore. Of course there's fucking empty space, space isn't entirely filled up with matter, that has nothing to do with what I was saying.
I'll have to take back one thing though. Funny that I had to check up on my own written projects with sources from some time ago to see that myself I wrote that dark energy is spread uniformly in the universe. I assumed that considering there would be larger densities of dark energy, there would also be regions where spacetime expands faster, but that notion seems to be wrong. Completely forgot this notion of the isotropic model of the universe, my bad.
>Our telescopes and observatories are getting better, and we're start to see more distant objects, does that mean our observable universe grows? No, that's not my point.
The point that I was replying to was that the observable horizon will no longer be spherical due to the expansion of the universe, which is doubly wrong.
>If you take the modern idea of the big bang
I would just chuck that right into the garbage, it was pulled from the Vatican library of stolen philosophical works and dusted off by a creepy priest of the church for one reason, they can still say God created it all. It is not a new theory, the original authors were probably just burnt on a stake some time ago. It has little scientific merit, is full of holes and stifles thought regarding more plausible scenarios, like a breathing expanding contracting eternal universe for one.
It's probably unpossible for man to understand the universe until better tools are invented, Hubble was certainly a start, too bad it was hobbled. It is a problem of scale and time that man cannot yet even comprehend let alone make presumptions about but speculation is encouraging.
Please take your ignorance elsewhere. Lemaitre's big bang specifically included a "primordial atom". Such a singularity does not exist in standard cosmology.
Modern cosmology is driven by observational power of models not dogma.
You're talking shit.