Okay, so apparently near the beginning of the big bang, everything was condensed into a singularity (or something similar), and then it all "exploded" away. That's the layman's afaik.
But if all of the energy and mass was condensed into such a small region of space, how come gravity didn't just pull it all back together again? It's not like the shit could travel faster than the speed of light, and the density was practically infinite
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Read about cosmic inflation. It really did expand faster than the speed of light.
That's why people talk about the observable universe and the unobservable universe.
How long would it have to inflate faster than the speed of light until all the matter and energy wouldn't be able to condense into a black hole anymore?
And in black holes, even light can't escape, and in a black hole is just a fraction of the mass and in a much larger space, how in the world all the matter and energy be able to escape the gravitational pull, even if the universe expanded faster than the speed of light
One of the most important implications about evidence of faster-than-light expansion is that it's a very strong indicator that the physics which describe now universe almost fully do not accurately describe such a period. So it doesn't even really make any sense to ask why it didn't turn back into a black hole, as we really don't understand why it did anything then (or at least, I haven't heard that there's an accepted model of physics for this time period.
Moreover, the faster-than-light dynamics I think of also as being generally motivated by stemming from the ultra-high-energy small-space physics of the very early universe, and even according to classical physics, gravity usually loses in small spaces. So it's not obvious that what you're proposing should happen would, even under current physics.
Finally, as a last bit of consolation, there is a property of differential equations that for a system which does not obey the conservation of energy, the system's behaviour is time dependent, and vice-versa. So if you want to think about the fact that energy seems to have been created at some point between now and time zero, then the math actually requires that equations which work now do not have to work then at all.
*now describe the universe
too much iterative editing. Also I'm missing a close-paren, but I don't think that will trip anyone up too much.
These are questions no-one really knows the answers to.
The reason for the postulation of cosmic inflation is to solve the Horizon and Flatness puzzles caused by assuming that the Universe began with a hot Big Bang. Which in turn is just an assumption based on the fact that we observe galaxies to be redshifted, and thus the space between us and the galaxy itself must be expanding.
To ask detailed questions about what gravity was back then is a bit meaningless too, because it was so incredibly hot at the instant of creation that all four forces were (hypothetically) unified into one big force with massless bosons.
So maybe gravity didn't work as it does now that early and thus inflation was allowed to happen. We can only speculate.
That was very insightful, thank you.
Wikipedia also has this "During inflation, the metric changed exponentially, causing any volume of space that was smaller than an atom to grow to around 100 million light years across in a time scale similar to the time when inflation occurred (10−32 seconds)."
So I guess I'm sorry for asking such a stupid question, it's just something that's been bothering me since my high-school physics teacher couldn't give a proper answer years ago
Np m8, school teachers are the worst. This is stuff I've only learnt recently at University and even then the lecturer could only ever wave his hands at it.
FYI the wikipedia page is full of great stuff, unsurprisingly. The stuff on de-Sitter space is particularly illuminating.
I'm still puzzled, as I'm reading on, it kind of feels conflicting to me,
>Further studies have since shown the expansion to be highly isotropic and homogeneous, that is, it does not seem to have a special point as a "center", but appears universal and independent of any fixed central point.
Wouldn't highly isotropic and homogeneous, combined with the big bang happening at one single point in space mean that there is an actual center?
If it's isotropic and homogeneous then the space right after the big bang must have expanded uniformly in all directions, leaving the origin spot of the big bang right there in the center, I don't know if my illustration is even logical now that I think about it, hell
To add, if all objects are moving away from us with speeds proportional to their distance, wouldn't that simply solidify the expansion, and in regards to the center, well, imagine it as a ball, getting ever smaller and smaller as the universe expands, it would still be there right at the center, but measurements would always be able to pinpoint it, no matter how large the distances between things grow.
Yeah I've been reading this for 20 minutes ago, it's a welcome change from maths pages, where if you don't understand it, wiki won't help, and if you do, the wiki is practically useless except for looking up some formulas or algorithms
Ahh!! Now you've made the classic "layman's" misunderstanding of believing the Big Bang to have taken place at a specific point in some abstract space. That simply isn't the case!
The Big Bang happened everywhere if that makes sense. Every single point in the Universe is expanding away from every single other point.
The analogy that made it clear to me was that of a balloon being blown up. Our Universe is the surface of the balloon. So if you were to draw two dots on the balloon when it's deflated and then blew it up the points would appear to be moving away from each from the point of view of these points. Yet the balloon isn't expanding from a singular point in that surface dimension.
The trouble with this analogy is people then assume that the Universe must be expanding into another space in a higher dimension, which is a bit of a stretch.
Does that kind of make sense?
Furthermore, it's not like we're all expanding from a single central point. If we were that would be very easy to see. Instead, in every direction we look, galaxies are receding from us at speed obeying [math] v = H_0 d [/math], where [math] H_0 [/math] is the Hubble constant and [math]d[/math] is their distance from us.
What line of thinking reaches the conclusion of Dark Energy? I mean, something is expanding the universe, but why does it have to be energy?
It's a placeholder term for whatever is driving the expansion. Just in the same way Dark Matter is used as the term for whatever caused galaxies to spin in the way that they do.
Check out these papers to see why (in my opinion) both i) Dark Matter and ii) Dark Energy are easily explained without making a load of new shit up:
i) arxiv.org
ii) arxiv.org
It does make a lot of sense but it leaves me with a problem, that there was already space before the big bang, or rather, at least some space, if we consider a singularity, that's a single point in space and then everything expanded away from it (the singularity being as small as in planck scale or who knows maybe even smaller), or if there already was space, then, well, yeah, there wouldn't be a center, but I was under the understanding that there wasn't any space beforehand.
Now that I think of it, even disregarding big bang entirely, if the expansion of the universe is isotropic and homogeneous, wouldn't that imply that it's a perfect (x), where x is sphere, or hypercube, or who knows, or could it still have those properties and be be an imperfect shape?
Oh, well that (maybe) uncomplicates things, I'm just a layman with no background in physics, it just seems weird to me, like it shouldn't be this way
I'm also assuming the formula you gave is not the full one, since every object has it's base speed, but then again I assume we can calculate that by removing the redshift factor and then calculating things.
From what I have gathered, the maths didn't add up, and there had to be something there to provide enough mass for the equations to add up
Yeah so now you're asking questions that physics can't solve. We can't answer what is outside of our Universe because we belong to it, and thus cannot leave it. You start entering the realms of philosophy and religion, which isn't particularly scientific.
The homogeneity and isotropy of the Universe is a global phenomenon/assumption. Clearly it isn't both since we exist, the point is that if you zoom out enough it will begin appearing as such. This is required because we observe the Cosmic Microwave Background to be (almost) homogeneous and isotropic. Thus the Universe must be also, since the CMB is a snapshot of the Universe after photon decoupling/freezeout.
Finally, that formula just for the recession speed. The full formula is:
[eqn]
\mathbf{v}_{rec}=H\mathbf{r}=\mathbf{v}_{pec},
[/eqn]
where [math]\mathbf{v}_{pec}[\math] is the 'peculiar' velocity, i.e. due to motion about some centre of mass, and [math]H[/math] is now the Hubble parameter that depends on time.
ahh fucked that equation up, rip
hopefully you get the gist regardless
Ah sorry, didn't realize I was delving into philosophy. The entire thing just kind of seems not right to me for some reason and I can't explain it.
And thank you for taking the time to answer the questions, I did get much out of it.
>tfw when reading about the edge of the Universe
I hate it
I just tell people that it bends into itself
No one knows because the Big Bang theory is flawed, incomplete solution to an incomprehensible problem. Take it, and pretty much all astrophysics on a galactic scale, as little more than nonsensical conjecture.
>The universe is expanding
>Logic suggests that perhaps it was expanding back then too
>Flawed solution
>I see a ball rolling down the street
>Logic suggests that perhaps the ball was always rolling down the street
>Flawed solution
A ball can stop rolling for a multitude of different reasons. The universe? Not so much.
>If I invent an invisible, undetectable dark aether the universe can expand forever!
>Perfect solution
Dark Energy =/= The Big Bang theory
Like we don't know how it happened but it's pretty obvious it happened
There's nothing preventing the contraction of the universe via gravity other than "increasing acceleration caused by dark XYZ"