Thread: the big bang

What is the big bang? I know the general concepts for it but I would like to understand more about what we are mostly certain about and what data we have that makes almost everyone very confident that there was the big bang.

Lets start out with what I think I understand about it.
We have data that every point in the universe is moving away from us.
Since it is not likely that we are in a unique place in the universe that probably means that every point in the universe is moving away from every other point
the farther out you go the faster things ( galaxies ) are moving away from us.
Since things now are moving away from us and will be farther away in the future then things were closer to us in the past. The farther you go back in time the closer things were
We are not sure what is causing the universe to expand and accelerate
The universe is homogeneous and isotropic
The farther we see the farther back in time we can see due to the time light gets here.
There are currently parts of the universe that are travelling away from us faster than the speed of light
There is a cosmic microwave background radiation

Now if all of the mass of the universe was packed close enough wouldnt it form a black hole?

Just a quick comment regarding your last question - "Now if all of the mass of the universe was packed close enough wouldn't it form a black hole?"

The answer to this is no.

A black hole is a region "in" space where spacetime is so warped that even light cannot escape. In the theory of the Big Bang space & time did not exist in the beginning. When the universe started to expand so space-time come into existence. The difference therefore being that If the universe started out from a single point "singularity" this point unlike black holes did not exist "in" anything.

Originally Posted by tom

...
The universe is homogeneous and isotropic
...

Au contraire. The Universe is neither homogeneous nor isotropic. We now know that the Universe has a structure that looks something like a foam. The galaxies form the walls of the bubbles. Few, if any, galaxies exist within the bubble voids.

Originally Posted by MisterMe

Au contraire. The Universe is neither homogeneous nor isotropic. We now know that the Universe has a structure that looks something like a foam. The galaxies form the walls of the bubbles. Few, if any, galaxies exist within the bubble voids.

Hmmmm...and this "foam" being similar in nature throughout and independent of direction one gazes upon it would seem to indicate that, indeed, the universe is both homogenous and isotropic...just saying....

Originally Posted by David E. Eaton Sr.

Hmmmm...and this "foam" being similar in nature throughout and independent of direction one gazes upon it would seem to indicate that, indeed, the universe is both homogenous and isotropic...just saying....

But that is not what homogeneous means. Homogeneous means to have uniform structure and composition. The Universe looks something like a sponge:



That is neither uniform in structure nor composition. Isotropic means the same in all directions. The Dark Matter map of the Universe shows that it is distinctly different in each of the three geometric directions:



If after seeing either of the above images, then you still believe that the Universe is homogeneous and isotropic, more power to you.

it sounds to me like the big bang is basically a REALLY big explosion. so big it's taken 13 billion years(so far) to cool down. that being said an explosion has to have a point of origin somewhere.

Originally Posted by Joe McCarron

it sounds to me like the big bang is basically a REALLY big explosion. so big it's taken 13 billion years(so far) to cool down. that being said an explosion has to have a point of origin somewhere.

yeah but not really an explosion ... here are a few of the issues.

If all of the mass of the universe was compacted close enough ... it would itself be a black hole and could not escape.
For an explosion there is an initial acceleration only and it would actually slow down due to gravity. However our universe is increasingly accelerating
There is no center point ... the entire universe is expanding in all directions ... everything is accelerating away from everything else in every direction.

Originally Posted by tom

yeah but not really an explosion ... here are a few of the issues.

If all of the mass of the universe was compacted close enough ... it would itself be a black hole and could not escape.

Tom, you're thinking in terms of what you know because you live IN the Universe. Your supposition assumes that there is something outside of the Universe for which to escape into.
Not necessarily.
If all the matter in the Universe was "Compacted" as per prior to sudden expansion- There would not be a Black Hole. A Black Hole can only exist In SpaceTime and AS a distortion of SpaceTime.
With the entire Universe "compressed," there is no gravity, no SpaceTime and no "mass or matter" as these constructs could not appear until a few billionths of a second after the sudden initial expansion.

Originally Posted by tom

There is no center point ... the entire universe is expanding in all directions ... everything is accelerating away from everything else in every direction.

Infinite but bounded or finite but unbounded?

Originally Posted by Neverfly

... ' Infinite but bounded or finite but unbounded' ?

... and thankyou for prompting my censorial cortex... if I have one..

If the universe was ever in a smaller space than the expanding mass it is now... then a argument for 'finite but unbound' is made.

For it to be infinite but bounded the observed expansion must not be so... as that would seem untrue. I am of the understanding we have little or no choice.

The universe is finite but unbound. Thats working on the principle that a infinite universe could not be contained in a smaller space..

for that to happen it must be finite. That a eccelorating expansion is evident then unbound \infty seems logical...

Originally Posted by MisterMe

But that is not what homogeneous means. Homogeneous means to have uniform structure and composition. The Universe looks something like a sponge:

::snip::

If after seeing either of the above images, then you still believe that the Universe is homogeneous and isotropic, more power to you.

What would it mean, if the Universe were homogenous?

If a swimming pool were filled with milk, would it be homogenous? What about starbucks foamed milk?

Serious questions, seriously.