# Question about time

1. May 17, 2005

### Nightsky

I don't have a mathematical background (Am acctually still in gr.10 in high school) but the universe has always interested me. I was thinking recently about time. If time slowed down, we would not be able to tell. Since everything would slow down in our mind.. We could not tell. What if time stopped. What do you figure would happen at that point.

By the way, I am new here. Hello everyone :-) I will maybe pop a math question into the math homework section sometime as well.

2. May 17, 2005

### Rebel

It is supossed that the time slowing keeps the same into your brain (if not you die in the process) if you agree that the laws of physics are the same independent of the system of reference. So you wouldnt experience it. If time stops in all frames of reference, there will be not universe (there would not be physical process),nor observers, if you are talking about one universe. (alhotugh the bad it seems like idea) thats the point to start with the idea developed from some people that there is not a point of "starting" of time.

Last edited: May 17, 2005
3. May 18, 2005

### Crosson

Because you say "the universe has always interested me" I will add that what you said about time applies to space also. If everything in space is expanding, it is impossible to tell.

Well, the universe is expanding, but the reason we can tell is that objects (like us) are not expanding with it.

4. May 18, 2005

### Enos

If time stops everywhere and starts again there will be no evidence that it stopped in the first place. When time stops so will all thought processes and all motions. But personally I'm not a big fan of time because it's trying to kill me.

Last edited: May 18, 2005
5. May 18, 2005

### Mortimer

You notice timeflow by motion and change. Motion is expressed as $$\Delta x/\Delta t$$ so in fact the actual timespeed is irrelevant for the calculation of motion as long as for every $$\Delta x$$ there is a matching $$\Delta t$$.
This remains valid even for $$\lim_{\Delta x, \Delta t \to 0}\frac{\Delta x}{\Delta t}$$ (you end up with 0/0 but this can be solved using l'Hopital's rules). So even if time stopped, we would not notice it.

Last edited: May 18, 2005
6. May 18, 2005

Staff Emeritus

It does NOT remain true in the limit. Limit of quotients is NOT the quotient of limits. This is the whole point of the limit concept and epsilontics.

7. May 18, 2005

### Nightsky

ok

Well I know that time slows down as we approach the speed of light. The universe had supposedly started as a singularity (this is the theory anyway) And our galaxy alone is quite a few LY in diameter. I am wondering if anyone knows how fast the earth is moving (Not just in orbit around the sun) this would include the rate at which our galaxy is moving. I would immagine we are moving near the speed of light due to the rapid expansion of the universe.

Is it possible that if you sat perfectly still in a dead area in the universe not under any influence of gravity or speed. And than came back to earth, would you... be in the future? Or just you and the atoms in your body would have aged faster? Roar its so confusing, yet so interesting :(

8. May 18, 2005

Staff Emeritus
Any serious textbook of calculus aimed at math students instead of engineers should have a discussion of the issues. Until the 19th century the idea that you got a derivative by dividing "little nothings" was common, and much derided by philosophers like Berkley. Then gradually the problem was understood and brought under control. In spite of the notaion, dy/dx is not a quotient, it is the limit of quotients whose numerators and denominations are finite numbers, not zero. Weierstrasse intorduced his epsilons and deltas in order to make these ideas rigorous.

9. May 18, 2005

### nwall

There are two ways to answer this: 1) There is no such thing as "sitting still". 2) You are always "sitting still". The second is really the most accurate way to say it. According to the general principle of relativity, "All Gaussian co-ordinate systems are essentially equivalent for the formulation of the general laws of nature" (Einstein, Relativity: The Special and General Theory, 108). Basically, what this means is that in order to say how "fast" you're moving, you have to pick something in the universe and say, "That's standing still." Then using this place you call "still" you can then state your velocity. Another approach would be to just claim that you are standing still, then you can base all velocities on your frame of reference.

However, as to the expansion of the universe, refer here: https://www.physicsforums.com/showthread.php?t=74478