Monday, June 05, 2006

An Introduction to Relativity

Einstein’s Theory of Relativity (both Special and General) are widely misunderstood concepts. This episode is going to present the basics of Relativity in a (hopefully) coherent and understandable manner. There will be no Creationist claim this week, as explaining Relativity should take all of our time today.

An Introduction to Relativity

Having trouble imagining time dilation? Check this out. This site is also great for understanding the Lorentz Contraction and the Twin Paradox.

8 Comments:

Blogger isefra said...

I'll definitely have to listen to that.

7:11 PM  
Blogger LushJ said...

Thanks for this fascinating breakdown of Relativity- I'm having problems with the "time" of "space-time" though. Logically, the time that light takes to travel through various situations (around a massive object like a sun or a black hole) doesn't affect the action of the images that it's depicting. For instance, if I'm on the other side of an eclipse break-dancing, I still dance at the same speed, but the image of me takes longer to reach Earth.

Where's the connection between what route light takes to reach the observer and "time"? I understand that relativity says that travelers @ the speed of light will age more slowly than the rest of us, but why?

Or is it just the appearance of slower/faster aging? If so, why does this matter?

P.S.- As a mid-30s person who thinks the intelligent design people are ridiculous, I really appreciate your from-the-ground-up approach to these blinkered fundamentalists. My wife is a devout x-tian and has no problem balancing her faith with evolution. I don't share her faith, but I share her belief in the scientific method.

1:16 AM  
Blogger Lucretius said...

The image of you can be warped when it arrives at an observer when there is a gravitational field between the two of you. Also, multiple images of the same object can be made as they are warped around such a field. If you look up "Einstein Ring" or "Einstein Cross" on a google image search you can see this for yourself.

The connection between the route light takes and time is this: because light is the cosmic speed limit, nothing can travel faster than it. This means, logically, that changes in time are decided by light — if it wasn't, light would travel back in time because it outpaces everything else. For instance, if time was decided by the electron, the photon, which travels faster, would get things done before the electron. If the electron decided time, the photon would go back in time because it is quicker.

Remember that time is all relative. If nothing in the universe moved, time could not exist. The reason people age slower when they are moving is this: the photons they emit take a longer path to an observer than they would if the person didn't move. They take a triangular path instead of a straight back and forth one — meaning more distance covered. Light needs to travel longer to "update" the image of the person you see. Yet, light decides time, and so the person does actually age slower. Odd thing to remember is that in the moving reference frame, the standing person ages slower, and they age normally.

Who really ages slower? Well, as long as one of them doesn't ever go back to find out, we have to say they both age slower. If one turns around, they lose their special reference frame treated by Special Relativity. They can tell they are moving — the one who turns around ends up aging slower due to the different times of redshift/blueshift that occur. I would look up the Twin Paradox on wikipedia and some other sites if I were you if you want to better grasp the idea.

Point is, we have empirically tested this concept of slower aging with atomic clocks flying in planes. Those that flew higher up ticked slower than those closer to the Earth due to the different strength of the Earth's gravitational field at the different heights.

I hope some of this helped, write back if you need any more help or didn't get what I wrote.

9:54 AM  
Blogger LushJ said...

Thanks for the quick thorough reply. I understand that HOW we measure time is affected by special relativity.

I just don't understand the connection between measuring the passing of time and the actual passing of time.

For instance, you have Tim or Mim or whomever in the car and on the porch, in their different references, fine. Physically, does one or the other age more quickly or more slowly? Do their bodies decay/age at different rates due to special relativity? I've always heard that if one travels at the speed of light towards another solar system, you age much less quickly than the people on earth.

3:32 PM  
Blogger Lucretius said...

The age we measure is necessarily tied to the actual aging of the person, otherwise we would find a violation of the inertial reference frame. If we measure someone aging at a slower rate, and yet their heart does not synchronize with that rate, then they can tell they are moving, and this violates the Inertial reference frame required by Special Relativity.

Light carries the information. The rate at which the information is exchanged is not simply an "illusion" — it actually IS, in this case, the rate of aging. Thinking that the person's aging is somehow the same is relying on the idea of absolute time. However fast light travels is how fast information can be exchanged. The information doesn't just provide the "appearance" of slower aging — the aging is actually slower. Again, we can't think in terms of absolute space and time. Einstein showed these don't exist.

5:17 PM  
Blogger LushJ said...

Gotcha. This explains it. I can't say I understand why, but I understand what Relativity says regarding time.

Thanks!

12:41 PM  
Blogger Punti said...

i was led to believe that the act of accelerating away from Stationary Sam (and back) would make Sam's twin "traveling Tim" return looking younger than Sam upon their reunion because Sam aged faster ?
...even if Tim closed the door on his way out & Sam wasn't able to observe Tim's travel ? (leaving light out of the equation).
P.S. They use to think that nothing could travel faster than sound !
If matter pops into existence: does its grav field instantaneously pop into existence...or does it reach out at the speed of light ? if grav field instantaneously pops into existence...then it exceeds the speed of light !
if grav field could be focused & used to pull/ accelerate a body then that acceleration would not be limited to the speed of light (as are std methods of propulsion) thereby allowing one to exceed the spd of light. What woul happen if you ran into a spec of dust @ the speed of light? Does anybody on this planet do work on gravitational anomoly generators ? Matter popping into existence: see "Big Bang"

2:20 PM  
Blogger Vito said...

I believe your questions can be answered by the scientists working on the hadron accelerator.

9:08 AM  

Post a Comment

<< Home