# The Naked Scientists Forum

### Author Topic: How does time change as one approaches the speed of light?  (Read 11728 times)

#### LetoII

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##### How does time change as one approaches the speed of light?
« on: 18/05/2012 01:05:29 »
I'm having trouble understanding what the speed limit means because as far as i understand it works like this: as you speed up time slows down on board. Thus if you measure speed by distance moved / time than doesnt this allow you to override the speed of light?
« Last Edit: 19/05/2012 15:48:44 by chris »

#### imatfaal

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##### Re: speed of light question
« Reply #1 on: 18/05/2012 11:51:22 »
Nope.  If I watch a space ship zoom past at a high relative speed - the time on it will be dilated from my perspective, but the length will also be contracted.  On board the ship nothing has changed.  Everyone still measures c to be c

#### LetoII

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##### Re: speed of light question
« Reply #2 on: 19/05/2012 09:24:57 »
thank you very much, however out of your answer a long existing question was brought back to life.
when you say lenght will be contracted you refer to the ship right? Is it however only contracted in lenght?

#### simplified

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##### Re: How does time change as one approaches the speed of light?
« Reply #3 on: 19/05/2012 18:34:48 »
thank you very much, however out of your answer a long existing question was brought back to life.
when you say lenght will be contracted you refer to the ship right? Is it however only contracted in lenght?

Refraction of  local motions creates length contraction.Interaction of kinetic energy and time makes speed.Change of a parity of kinetic energy and cooperating time makes refraction.Directions of local movements concerning the general movement define abilities of the energies to cooperate with time.
« Last Edit: 19/05/2012 18:41:18 by simplified »

#### Phractality

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##### Re: How does time change as one approaches the speed of light?
« Reply #4 on: 20/05/2012 01:09:22 »
I'm having trouble understanding what the speed limit means because as far as i understand it works like this: as you speed up time slows down on board. Thus if you measure speed by distance moved / time than doesnt this allow you to override the speed of light?
As you accelerate close to the speed of light, the distance to your destination shrinks. If the distance was 10 light years, and you accelerate quickly to .9 c, the distance will shrink to 4.36 ly, and clocks at the destination will advance by 5.64 years while you are accelerating. You then coast 4.36 ly in just 3.92 years by your clock. While you are decelerating at your destination, the distance returns to 10 ly, and clocks at your starting point advance by 5.64 years. Now the stationary clocks at both ends show 11.11 years, but your clock shows 3.92 years. To you, it seems like you went 2.55 c. But to stationary observers, you only went .9 c.

#### LetoII

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##### Re: How does time change as one approaches the speed of light?
« Reply #5 on: 21/05/2012 01:08:55 »
that's an amazing way of describing travel at light speed Phractality. Thanks for your time and knowledge.
- Since the distance shrinks for me at lightspeed is it safe to say it's the universe itself that shrinks in respect to my speed? So not just the space between me and the destination.
- since you explain it in this fashion do you believe it's possible to go beyond light speed?

#### Phractality

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##### Re: How does time change as one approaches the speed of light?
« Reply #6 on: 21/05/2012 04:11:38 »
Since the distance shrinks for me at lightspeed is it safe to say it's the universe itself that shrinks in respect to my speed? So not just the space between me and the destination.

From your perspective while you are traveling at .9 c, the whole universe is contracted in the direction of relative motion. Galaxies which were 10 billion light years away when you were still become 4.36 billion light years away in the time it takes you to accelerate to .9 c. If you reached .9 c in .001 year, those distant galaxies got closer at a rate of 564,000,000,000 c. However, that is not considered to be a velocity.

Meanwhile, from a "stationary" observer's perspective, YOU are shrunk in the direction of travel.

- since you explain it in this fashion do you believe it's possible to go beyond light speed?

The speed limit applies only to how fast you can pass things, and it is measured in the observer's meters and seconds. In your reference frame, you are passing things at .9 c; in a "stationary" observer's reference frame, you are passing things at .9 c.

I have my own way of explaining WHY matter cannot go faster than light; in a nutshell, matter IS light; but that belongs in New Theories. Faster than light communication is probably also impossible. There is some evidence that it may be possible for cause and effect to be connected instantaneously (in a preferred reference frame), via quantum entanglement, but this can only be verified after a light speed delay.

#### LetoII

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##### Re: How does time change as one approaches the speed of light?
« Reply #7 on: 21/05/2012 19:33:08 »
My own view of matter is that matter is light and space, but like you said that's a whole different section.
What i still have a tough time understanding though is how a human going at .9 C could be doing just fine while at the same time its impossible to go faster than the speed of light.
while accelerating all thats required for the humans well being aside from radiation protection is a low enough acceleration so that he doesnt get too much G to handle.

#### Phractality

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##### Re: How does time change as one approaches the speed of light?
« Reply #8 on: 22/05/2012 05:45:47 »
while accelerating all thats required for the humans well being aside from radiation protection is a low enough acceleration so that he doesnt get too much G to handle.

We could withstand considerably greater acceleration if we could be frozen solid. Then, we still have the problem of different parts of the body being different densities. Filling the lungs with a special fluid helps.

Another problem is the conservation of momentum and energy. The most efficient propulsion system that can be postulated would convert matter and antimatter to a laser beam at 100% efficiency.

In Earth's reference frame: The ship's rest mass is M0; Gamma of .9 c is 2.294, so the momentum of the ship would be p = 2.294 M0 * .9 c = 2.0646 M0c. The momentum of the laser beam would be equal and opposite the momentum of the ship. The rest mass of fuel converted to the laser beam would be p/c = 2.0646 M0.

If you want to decelerate to zero at the destination, you have to have 2.0646 M0 of fuel (in the ship's reference frame) remaining after you reach .9 c. So you have to consume 2.0646 * 3.0646 M0 to get started and 2.0646 M0 to get stopped. Your fuel's rest mass at the start would be about 8.4 M0.

If you plan to make it a round trip, carrying your fuel for the return trip with you, then you must begin with roughly 70 M0 of fuel. If your engines have constant thrust, this makes your starting acceleration 64 times slower than your ending deceleration at Earth.

Efficient laser drive engines are probably centuries away. When we do get them, we'll have to be careful not slice the Earth in two with our exhaust.
« Last Edit: 22/05/2012 05:49:32 by Phractality »

#### LetoII

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##### Re: How does time change as one approaches the speed of light?
« Reply #9 on: 22/05/2012 10:39:50 »
last thing i heard of concerning "freezing" us is glassification, it seems to be the best shot at freezing us in time. that should work :)
back to the scenario though, even though mass increases in our equations when we speed up this doesnt seem to affect any humans inside the vehicle at all. doesnt this mean we have to clarify this mass increase more clearly than we currently do?

#### Phractality

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##### Re: How does time change as one approaches the speed of light?
« Reply #10 on: 22/05/2012 16:33:45 »
even though mass increases in our equations when we speed up this doesnt seem to affect any humans inside the vehicle at all. doesnt this mean we have to clarify this mass increase more clearly than we currently do?
We have been discussing that issue at
On the concept of relativistic mass.
In the reference frame of the ship, there is no mass increase.

#### LetoII

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##### Re: How does time change as one approaches the speed of light?
« Reply #11 on: 23/05/2012 02:31:51 »
taking relativistic mass into account you can explain things like:
- why it's more efficient to accelerate slowly than doing it very fast
- how it is that although there is more mass added in equations it takes the same effort / fuel to add acceleration no matter what the current speed.
right?

#### flr

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##### Re: How does time change as one approaches the speed of light?
« Reply #12 on: 13/06/2012 19:35:25 »
Refraction of  local motions creates length contraction.

Refraction? Refraction of what?

#### The Naked Scientists Forum

##### Re: How does time change as one approaches the speed of light?
« Reply #12 on: 13/06/2012 19:35:25 »