I’m reading Stephen Hawking and I understand about 0.052 percent of what he’s saying, but have a few questions that I think will help me understand a lot more of what the big bang is about.

1. My understanding of Hawking is that scientist based the big bang theory on the fact that the universe is expanding. To me that’s very big leap. . How did they get from the phenomenon of an expanding universe to the conclusion that the universe began 10 to 13 billion years ago? there are so many variables that have to be taken into account to make such a calculation—the rate and duration of periodic accelerations, the effects of gravity on acceleration, the effects of collisions on acceleration
2. Is the Doppler Effect the only evidence scientists have that the universe is expanding?
3. How do scientist know what size the universe was when it started expanding? We cannot say how long it took to get from point A to point B if we don’t know what point A was.

The temperature and fluctuations of the cosmic microwave background, the cosmic redshift of supernovas, the structures found in large scale galaxy distributions and the abundance of light elements together give us enough data points to fix the age very precisely, and to be very certain that the universe was once hot and dense.

http://science.howstuffworks.com/diction...theory.htm

I just have to complain about one thing that is conceptually wrong, but creeps into every popular explanation - the expansion being " faster than the speed of light" is not a good description of what happens.

(July 11, 2016 at 3:02 pm)Alex K Wrote: I just have to complain about one thing that is conceptually wrong, but creeps into every popular explanation - the expansion being " faster than the speed of light" is not a good description of what happens.

Why?

(July 11, 2016 at 3:12 pm)RozKek Wrote:

(July 11, 2016 at 3:02 pm)Alex K Wrote: I just have to complain about one thing that is conceptually wrong, but creeps into every popular explanation - the expansion being " faster than the speed of light" is not a good description of what happens.

Why?

Because cosmic expansion, in the language of Einstein's relativity, is not objects moving * through space * at ever greater speeds, but rather space expanding. All distances get multiplied by a factor increasing with time, the so called scale factor. Since nothing really moves through space in cosmic expansion, it only makes limited sense to assign the increase in distance over time to a velocity. If the universe is big enough, even moderate expansion rates will give you effective distance increases per time that would correspond to faster than light velocities. Casting it in that language makes it appear as if there was a contradiction with the cosmic speed limit when there isn't.

I give you an analogy: imagine two snails on a rubber band sitting 2 feet apart. They can only crawl one foot per minute max. Now you pull the rubber apart such that its length doubles in 10 seconds. The snails will now suddenly be 4 feet apart. Did they magically crawl 1 foot in ten seconds each, thus beating their own speed limit? No, the distance between them increases because the rubber stretches, and theirn distance has increased at 2 feet per 10 sec, but at no point did they exceed their max crawl speed on the rubber!

So it would be more accurate to say that the expansion happens faster than the speed of light can propagate information across the area being spread?


I have no fucking clue what I'm saying, but you know that already.

2)

beside the Doppler effect, there is a correlation between dimness and apparent size of the galaxies we see. Hubble Space Telescope can see amazingly faint galaxies and in the pictures they are tiny compared to the bright nearby ones.

And the nearby ones can have their distance measured by techniques not involving Doppler shifts of their light. So, whenever a new telescope reveals more fainter and tinier looking galaxies, a very simple explanation is they are further away than the ones that are brighter and appear larger.

Astonishingly faint galaxies are astonishingly far away.



And just observing a Doppler shift in a galaxy's light isn't the only thing Dopler can do for us. If a star explodes and we note the side of the debris cloud facing us is approaching us at 10% of the speed of light, then we know that perpendicular to a line to us, the debris is also expanding at 10% + 10% (for each side) the speed of light, so if we look again in 10 years and see the debris cloud looks bigger, simple geometry can give a surprisingly accurate distance.

for example:
If I am watching a kid blow up a balloon miles away thru a telescope, and make a rough estimate of how fast kids can blow up balloons, knowing the magnification of the telescope and how big the balloon appears to be getting, I can figure out (if I were younger and remembered high school geometry better) how far away the kid is.

If I just assume all balloons are the eventually the same size, I can figure how far away all the balloons I can see are.

Technique would be similar for cars instead of balloons, stars instead of cars, galaxies instead of stars. If I figure out there are different kinds of stars then I can be more accurate if I figure out what kind of star I'm looking at, same for galaxies, the more I know the more I can find out.

The spectrum of distant galaxies also show absorptions at different Doppler shifts from gas clouds between here and there. And the further out we think we are looking, how about that, more lines of absorption appear because there are more gas clouds along the way.

It all hangs together. We don't see stars that are Cepheid variables in galaxies shown to be too far away for us to see them. So, things we don't see also help. As telescopes improve, we can see Cepheid variables further and further out, lo and behold, they are are consistently distant with the distances already worked out via other means. So stuff we didn't see because it was too far/too faint at one time, that later becomes visible with better equipment helps establish confidence in what was worked out before with lesser equipment.

At some point (I believe the estimate is 30-40 years) we should have equipment to directly detect changes in the Doppler shifts of extremely distant objects that are caused by a possible acceleration affect, or rule out that theory if a decel is detected.

Unlike religion, cosmology doesn't need special pleading, reliance on 'belief', or preconceived dogma to work out things. Someone comes up with an idea, develops an observation strategy to confirm/deny the idea, gets a confirmation observation(s) from somebody else, and you've got something.

Awesome.

(July 11, 2016 at 2:19 pm)Alex K Wrote: The temperature and fluctuations of the cosmic microwave background, the cosmic redshift of supernovas, the structures found in large scale galaxy distributions and the abundance of light elements together give us enough data points to fix the age very precisely, and to be very certain that the universe was once hot and dense.

Remarkable. I’m reading about the CMB right now. So it seems that was your primordial soup of loose fermions and bosons that eventually combined into atoms. I wonder, is the CMB showing up in the red, i.e. moving away? And why is it called recombination, as if it had happened before?

I want to read further to get a better understanding of how the CMB is an “echo of the Big Bang.” So far, my lay conclusion is that the isotropic nature of the CMB supports Jonathan Strickland’s (author of Min’s link) statement that this was not an explosion.

I will look at the other things you listed, but not tonight. Going to bed, g’night. Sleep tight.