Author Topic: Build a time machine (Read 800 times)

SageFIN · « **Reply #15 on:** May 10, 2005, 06:20:04 PM »

Quote

Originally posted by NUKE
I don't get it. What if she had a super telescope and watched the earth's rotation and traveled away at the speed of light. She observes the earths physical rotation and times her return to coincide with one rotataion. One physical rotation.

How could the the earth have rotated more than one time for the people on earth as well? Or did she not see the other rotations?

That's what I'm getting at, time as measured by the rotation of the earth for both people. How could they be different?

Because Sally shouldn't measure the passage of time by the rotation of Earth (around it's axis or around the sun, whichever) but by some accurate timepiece that is travelling with her in the rocket. Were she to look at the Earth with a powerful telescope, she would see that it goes around faster than usually.

So, both the spacefarer and the groundpounder observe equal number of rotations of Earth. For the fellow in the spacecraft, they just seem to go by in a shorter time.

Darkish · « **Reply #16 on:** May 10, 2005, 06:20:21 PM »

Ok.. the problem is with the issue of observation, and that is the heart of relativity.

Think of it this way.. you're on a train and toss a ball up and catch it: to you the ball went straight up and down - to someone looking into the window as the train passed the ball was also moving along at 60 mph as well as going up and down.

So you can have one event that looks very different depending on where you're observing.

NUKE · « **Reply #17 on:** May 10, 2005, 06:24:34 PM »

Quote

Originally posted by Darkish
Ok.. the problem is with the issue of observation, and that is the heart of relativity.

Think of it this way.. you're on a train and toss a ball up and catch it: to you the ball went straight up and down - to someone looking into the window as the train passed the ball was also moving along at 60 mph as well as going up and down.

So you can have one event that looks very different depending on where you're observing.

I understand that. What I don't understand is the given example of Sally travelling away at high speed, for what seems like a year for her, but in reality was ten rotations of the earth both for her and the people on earth.

The rotations of the earth cannot change physically for either of them. So for either person, 10 rotations went by regardless of how it was percieved by either one.

Darkish · « **Reply #18 on:** May 10, 2005, 06:26:50 PM »

Sage nailed it.

Gh0stFT · « **Reply #19 on:** May 10, 2005, 06:26:53 PM »

Nuke: :"She observes the earths physical rotation", , she cant,
imagine she have to fly at light speed, or at least very close to it.
So light from the back (i.e: earth) is not visible or at least they
would look strange. The light frequencies go from visible to ultraviolet or beyond, length-shrunk images, distorted by aberration and bizarre time effects.

ah and btw an very easy describing of the theory of relativity is something like this:
Moves the earth around the moon? or the moon around the earth?
a person sitting on the earth will see the moon travel,
a person sitting on the moon will see the earth travel around.
]

ChickenHawk · « **Reply #20 on:** May 10, 2005, 06:32:32 PM »

Quote

Originally posted by Darkish
The thing is Nuke, that for the girl in the ship the Earth went round the sun only once.. is all relative see.

No, for the girl in the ship the Earth went around the sun 10 times but did it 10 times faster than normal (ten times in one year.)

What I find interesting is that for particles traveling near the speed of light, the universe around them is much much slower. So in effect, they can travel the length of the galaxy in minutes rather than tens of thousands of years.

So does that mean it wouldn't take four years at the speed of light to reach Alpha Centari?

Did it really take billions of years for the light of a distant star to reach Earth?

Perhaps a resident physicist could shed some light on the subject.

eskimo2 · « **Reply #21 on:** May 10, 2005, 06:36:08 PM »

Quote

Originally posted by NUKE
I understand that. What I don't understand is the given example of Sally travelling away at high speed, for what seems like a year for her, but in reality was ten rotations of the earth both for her and the people on earth.

The rotations of the earth cannot change physically for either of them. So for either person, 10 rotations went by regardless of how it was percieved by either one.

Yes, 10 Earth years went by for her too. But, she only aged 1 year and experienced a year's worth of happenings. Think of all she could have earned on interest, and she's only a year older!

eskimo

Gh0stFT · « **Reply #22 on:** May 10, 2005, 06:37:46 PM »

Quote

Originally posted by ChickenHawk
What I find interesting is that for particles traveling near the speed of light, the universe around them is much much slower. So in effect, they can travel the length of the galaxy in minutes rather than tens of thousands of years.

So does that mean it wouldn't take four years at the speed of light to reach Alpha Centari?.

No, thats exsactly the relativity theory, it depends from the point of view.
For the Person inside the starship, 1 lightyears is 1 lightyear.
He would travel 4 Years to AC.

NUKE · « **Reply #23 on:** May 10, 2005, 06:39:30 PM »

Quote

Originally posted by ChickenHawk
No, for the girl in the ship the Earth went around the sun 10 times but did it 10 times faster than normal (ten times in one year.)

What I find interesting is that for particles traveling near the speed of light, the universe around them is much much slower. So in effect, they can travel the length of the galaxy in minutes rather than tens of thousands of years.

So does that mean it wouldn't take four years at the speed of light to reach Alpha Centari?

Did it really take billions of years for the light of a distant star to reach Earth?

Perhaps a resident physicist could shed some light on the subject.

That's a good explaination. It is very interesting to think about travel near the speed of light.

Just think, if we where able to lauch a ship from earth, travel to Alpha Centari and return at near the speed of light, all the people on earth may well have been long dead upon your return.

So in order for the people on earth and science to advance or learn from your experiences, they would have to wait generations, while meanwhile as you returned, techology on earth will have far surpassed it's state from when you left.

SageFIN · « **Reply #24 on:** May 10, 2005, 06:41:50 PM »

Quote

Originally posted by ChickenHawk
No, for the girl in the ship the Earth went around the sun 10 times but did it 10 times faster than normal (ten times in one year.)

What I find interesting is that for particles traveling near the speed of light, the universe around them is much much slower. So in effect, they can travel the length of the galaxy in minutes rather than tens of thousands of years.

So does that mean it wouldn't take four years at the speed of light to reach Alpha Centari?

Near the speed of light it would take less than four years, as observed by the travellers. If observed from Earth, the trip would take slighty longer than four years.

GhostFT: The traveller in the spaceship would see the distance to Alpha Centauri shortened by the Lorentz contraction.

This is why muons can penetrate so deep into the atmosphere despite having too short of a half life to otherwise get much anywhere -- they move so fast that the distance appears contracted to them. The other side of the coin is that from the perspective of an observer on the surface of the Earth, the passage of time of the muons is slower, and thus it balances out.

Quote

Did it really take billions of years for the light of a distant star to reach Earth?

It did, from our perspective.

Holden McGroin · « **Reply #25 on:** May 10, 2005, 06:42:07 PM »

If you cannot get the time dialation of Sally, Nuke, you're really going to have a fun time with this.

Two spaceships pass each other in deep space. Relative to each other each is traveling at the near speed of light. Each can truthfully say that they are the inertial reference and the other is speeding along.

Relative to ship a, ship b is aging more slowly.

Relative to ship b, ship a is aging more slowly.

NUKE · « **Reply #26 on:** May 10, 2005, 06:45:20 PM »

Quote

Originally posted by Holden McGroin
If you cannot get the time dialation of Sally, Nuke, you're really going to have a fun time with this.

Two spaceships pass each other in deep space. Relative to each other each is traveling at the near speed of light. Each can truthfully say that they are the inertial reference and the other is speeding along.

Relative to ship a, ship b is aging more slowly.

Relative to ship b, ship a is aging more slowly.

I understand the relative motion and how it depends on your perspective. I just need to get drunk and listen to some Hank to let it all sink in I guess

p.s., who got Sally preggers?

Gh0stFT · « **Reply #27 on:** May 10, 2005, 06:53:43 PM »

Holden McGroin i love such examples, but dont forget, we dont
travel at light speed and i doubt we will evar.
So, no lightspeed = no time travel and no headache from
freakin RT questions

...back to my whiskey glas

WMLute · « **Reply #28 on:** May 10, 2005, 08:08:57 PM »

still waiting for someone to show me how time is a force, as opposed to a measurment.

john9001 · « **Reply #29 on:** May 10, 2005, 08:34:55 PM »

it's already been proven, two syncronized atomic clocks, one kept on earth the other sent into orbit, after landing the orbiting clock, the two clocks showed different times.