Garbles18

I am curious how it can be stated that the universe was like (insert state) at 10 E -34 seconds after the Big Bang when the concept of time would have a completely different meaning at that time. Relativity has shown that time changes for something based on the velocity of that thing. Whether you accept inflationary model or not, the universe was obviously moving very fast for a period of time after the Big Bang.

If this doesn't make sense, let me put it this way. What does 10 E -34 seconds mean at that time? Do they mean 10 E -34 of our present day seconds? Or do they mean 10 E -34 of how ever long a second was in that instant? Because I don't see how one second can have the same meaning for that instant in time as it does to us on Earth now.

eh

Keep in mind that relatvity predicts the laws of physics will be the same to all observers. So no matter what speed you are going, the laws of physics hold true.

The early universe likewise should act according to the same physics we have today.

Garbles18

Well, what I'm saying is that even though the physics would be the same, how would time be effected? It's like the idea that if you get in a rocket and fly around at the speed of light for what you believe to be a year, a lot more time would actually pass on Earth. Time goes slower for things moving faster. So, if the very early universe was expanding so incredibly fast, what does it mean to say that something happened at such and such time immediately after the Big Bang?

In other words, what frame of reference are they using? Since time slows down when something speeds up: did 1 second actually take a really long time in the first several moments of the Big Bang; did 1 second actually take 1 second; or does 1 second even have any real meaning since we base time off of the oscillations of an atom that didn't even exist in the first moments of the Big Bang?

AtomSmasher

I believe the reference frame is that of an external obsever with time being relative to what it is now. Therefor the observer would be outside the inflating universe and time would be relative to his own frame of reference. It would be rather complicated to model realistic observations from within the inflating universe, so we ignore quite a few relativistic effects when describing the universe. That's just my take, I'm no physicist but I bet you'd get some good answers in the cosmology forum on www.physicsforums.com.

cfgauss

The "observer" would just be someone that's hanging around amidst all the stuff going on. There's no problem with doing that. In fact, it's "really" no different than describing what happens to an exploding star (but more complex, obviously).

capnkirk

Gauss,

What we really need here is some input from knowledgeable sources...I peeked at your profile and see that you are a theoretical physics major. with an interest in astrophysics. PLEASE, help us out here by pointing out the misunderstandings about relativity. Most people believe almost as mny myths about relativity as they do about religion! I, as an engineer trained in physics but not in relativity, would gladly defer to someone who can speak more authoritatively than I can. :notworthy

Garbles18

So, my next question is: If the times of post Big Bang events are found from an objective frame of reference, how do they calculate when things occured when they are a part of the system? It seems to me that everything we can observe in our universe and extrapolate back to the Big Bang would be skewed by how time changes as you get closer to the Big Bang. So how do they seperate themselves from that to make objective calculations?

cfgauss

Well, if you really want to understand it you've got to get a textbook in it and go through it; any explanation short of that will leave you (at least partly) confused.

But let me try to illustrate several important points:

Try to think of "time" not as time, but as a special axis on a coordinate system on which we always move on with a nonzero velocity. You can interpret this geometrically as a graph on some x,t coordinate system, or as several "snapshots" of something in space. Thus, when an object is effected by time dilation it is going faster or slower through this "time-axis." Now, this does not necessarily represent how things actually are in relativity (it's actually more along the lines of what I think should be emphasized more in Newtonian physics), but it does give a nice intuitive foundation to build off of.

Now, also remember that problems only start to arise in which relativity is needed when you try to talk about something that is (or was) "over there," instead of something that's "here." In fact, many relativistic things look much like they should according to Newtonian mechanics! For example, if I send a space ship on a round-trip to Alpha Centauri, 4 light years away, at 90% c. The people on Earth watching them go away will see things exactly as Newtonian mechanics says so! They will see the space ship take, as Newtonian mechanics says, about 18 years. However, the people onboard the ship will claim that only about 8 years have passed. The reason for this is that, like I said, the problem only occurs when you try to talk about someone "over there." (A bit tangent to this, time dilation is only caused by velocity, it is not affected by acceleration, jerk, or anything else! Although the equations get uglier, because you have to sum up a bunch of dilations for 'each' velocity it's at.)

It's the same thing with the big bang. There's no problem with us talking about it, using "our" time and everything. The only problem would occur if we were to ask a particle created in the big bang how old it was!

Does that make any sense?

If you want a great introduction to relativity, I *strongly* suggest:
"A Journey into Gravity and Spacetime" by John Wheeler.
It is a most excellent book!

If you want a great text in it, I suggest "Spacetime Physics" by Taylor and Wheeler. You can find both on amazon.com.

Shake

I've read some stuff by Wheeler before. He's very good at explaining these sorts of things even for those of us who aren't physicists.

Garbles18

Okay, I understand your point that asking a particle created at that time how old it is would create a problem because it would have a different frame of reference than us. And I realize that a large part of my problem of understanding this is that I don't know how exactly calculations were made about events after the Big Bang. Do the books you suggested talk much about the specifics of Big Bang or are there books that focus more on it without being 100% math?

Thank you for the suggested reading. I will read the Wheeler books when I get a chance and hopefully that will help me in my understanding.