Light speed and time

I posted this on another thread but got no response. I am lysdexic and so is my whole famned damily, that is the reason I have trouble with the math.



I would like to ask a question. First I will need to set up three scenarios, these are based on what I know about Einsteins theory stating that traveling at the speed of light will effect time. Although I do understand much of it, I am lost in the math that explains it.

From what I understand:
Einstein worked out his idea with the use of a magic clock. Einstein used a magic clock in his example because if we were actually moving away from the clock we would loose sight of it very quickly. What we see when we look at a clock is not the clock but the light that is reflected from the clock. If we move away from the clock at the speed of light, we would always see the same light particles and therefor time would stop for the people on the ship that are moving away.

Scenario one:
The occupants of the ship leave Earth at the speed of light. To them time has stopped since they are traveling at the speed of light. They travel to a star system that is four light years away.
Results:
To the crew this trip would be instantaneous but to an observer on Earth the trip took four years.

Scenario two:
In this scenario we will use the same set up as in scenario one except we will look at the return journey
The crew leave the new world for the journey home. The crew still see the magic clock back on Earth.
Results:
From an Earth perspective the trip to a new world took four years and the return trip took four years.
The crew of the ship would see this completely different. To the crew the journey to the planet was instantaneous but the return trip took eight years. They are moving toward the magic clock at the speed of light and the light being reflected from the clock is moving toward them at the speed of light. Just as two cars traveling at 55mph collide at the same rate as a single car hitting a wall at 110mph the collision of the light particles would be doubled and therefore time would appear to double for the crew.

Scenario three
For this example I will add two new timepieces, a magic clock on the new planet and a wristwatch on the crew member of the ship. Again we will look at the complete trip to and from the new world
Results:
From Earth the trip to the new world has taken eight years, four years to get there and four years to get back.
To the crew they would look at Earth and time would seem to stop but when they turn around they would see the clock on the new world spinning at twice the normal speed. The wrist watch on their arm would be traveling or ticking by at normal speed/time. To the crew, the journey to the new planet takes four years and the return trip takes four years. The exact same as the witness on Earth sees.

As I said, I really don't know much about Einsteins theory but this seems to present a paradox. I hope that a member of this forum has the knowledge to explain the mistakes in my theory. If I am correct then the whole idea of time traveling at the speed of light is incorrect.

Time dilation is not dependent on observing the "magic clock". It occurs without it.

1) For the crew the rate of time does not change. For "us" the clock on the ship slows down. For "them" our clocks speed up. For them the trip takes four years. From their point of view we have aged more than four years. From our point of view, they have aged less than whatever amount of time it takes them to get to the other star.

2) Same thing. The direction of travel makes no difference. It is the speed that causes the effect.

3) For us, Earth will have aged something more than eight years and the crew will have aged somewhat less than that.

Of course, we are ignoring acceleration and deceleration, which also have an effect on time dilation.

[edit on 8/1/2010 by Phage]

As usual phage has nailed it. Relativity is the key.

I remember arguing the two cars heading towards each other scenario when I was younger. It's counter intuitive, but thats the beautiful head*snip* nature of the subject.

Well that is the part I do not understand. Time is relative to the observer, why is the time I posted not correct? I am actually trying to understand this.
Someone on earth would see time slow for the people in the ship while those on the ship would see earth time speed up? If time is relative to the observer wouldn't the people on the ship see time moving at an increased speed?

I'm not trying to argue here, I am simply having a hard time wrapping my mind around this. I still can't figure out what Hawkings meant when he asked "Why do we remember the past but not the future?" either.

reply to post by Phage


so phage, perhaps you can answer a question i have....

In the deep, dark recesses of intergalactic space, there is a stark absence of matter.

In such an environment, completely devoid of time dilation, what happens to the interstellar traveller? How does their mass impact the time dilation in their immediate vicinity?

the light from other galaxies...how do we age it? The time it taks to traverse the distance from there to here....how do we fix that? Would tthe lack of matter/energy not effect how long it took that light to reach us?

reply to post by ChicUFO

Don't feel bad. It is hard to grasp but it really does happen.

Within a given frame of reference time "flows" at a normal rate. Outside of that frame of reference the rate is variable. A difference in gravity, acceleration (which is actually the same thing as gravity), and velocity will put an object in a different frame of reference from the observer. For the observer of the other frame of reference time in that frame of reference is variable.

Hawking did not originate that quote. I don't know who did but I first heard it when I was a teenager and that was a long time before Hawking wrote A Brief History of Time. It's more of a philosophical question than a physics question but the easy answer is that the future, our future, has not happened yet.

I found this:

And so I learned a lesson
Which I ought to have known before,
And which, though I learned it dreaming.
I hope to forget no more.
So I sit alone with my conscience
In the place where the years increase,
And I try to remember the future
In the land where time will cease.

-Conscience, Charles William Stubbs (1860-1946)


[edit on 8/1/2010 by Phage]

reply to post by Phage


I appreciate that explanation, it is much clearer than your first post in this thread.
I believe that I understand it a little better but I simply have to many questions. I wonder what will become of this theory if Dr Erik Verlinde claims prove to be true. Dr Verlinde believes that gravity does not exist, something I have considered for a while myself.

Gravity does not exist

reply to post by ChicUFO

Time dilation occurs. GPS satellites are adjusted to account for it.

The engineers who designed the GPS system included these relativistic effects when they designed and deployed the system. For example, to counteract the General Relativistic effect once on orbit, they slowed down the ticking frequency of the atomic clocks before they were launched so that once they were in their proper orbit stations their clocks would appear to tick at the correct rate as compared to the reference atomic clocks at the GPS ground stations. Further, each GPS receiver has built into it a microcomputer that (among other things) performs the necessary relativistic calculations when determining the user's location.

www.astronomy.ohio-state.edu...

I think the whole idea is easier to understand if you think of time as flowing or moving at the speed of light. If you travel close to the speed of light, you experience a lot less time because you're traveling almost as fast as time is flowing.

It's similar to watching how much water flows down a fast moving stream in your vicinity. If you're in the river in a canoe traveling about the same speed as the water, the water (or you could say time) doesn't seem to change much (same batch of water is traveling with you). However if you're standing on the shore watching, you see a whole lot of water pass by you.