# Aging When Travelling

relativity

36 replies to this topic

### #18 OceanBreeze

OceanBreeze

Creating

• Moderators
• 1243 posts

Posted 21 May 2017 - 01:55 PM

But this...

... is time dilation alone, meaning that the journey in proper time would be 377.47 years if length in space weren't contracted, and this...

... is length contraction alone, meaning that the journey in proper time would be 377.47 years if length in time weren't dilated.

Are you saying that both ways of doing it take both time dilation and length contraction into account? It doesn't look like it.

I am saying that the Lorentz transform is used to solve for dilated time, independently of contracted space, AND the Lorentz transform is used to solve for contracted space independently of dilated time.

When used together in a ratio of contracted distance / dilated time, you get the velocity, which is the same for both the travelling observer and the stay at home observer.

You seem to think there is some sort of feedback at work, such that the shorter the distance, the more dilated the time and that is not true. If that were true, then the more dilated the time, the shorter the distance ad infinitum, and you never arrive at a final answer for either time or distance!

### #19 A-wal

A-wal

Creating

• Members
• 1324 posts

Posted 21 May 2017 - 02:18 PM

I am saying that the Lorentz transform is used to solve for dilated time, independently of contracted space, AND the Lorentz transform is used to solve for contracted space independently of dilated time.

Yes but to get the proper time you need both. It's the amount of time (that's dilated) it takes to cover the space (that's contracted).

When used together in a ratio of contracted distance / dilated time, you get the velocity, which is the same for both the travelling observer and the stay at home observer.

Yes exactly.

You seem to think there is some sort of feedback at work, such that the shorter the distance, the more dilated the time and that is not true. If that were true, then the more dilated the time, the shorter the distance ad infinitum, and you never arrive at a final answer for either time or distance!

No, but it looked like he was using one set of equations to get time dilation and working out the journey time from that and then doing the same thing with length contraction without ever combining the two to get the actual proper time that the journey would take.

### #20 OceanBreeze

OceanBreeze

Creating

• Moderators
• 1243 posts

Posted 22 May 2017 - 03:44 AM

Yes but to get the proper time you need both. It's the amount of time (that's dilated) it takes to cover the space (that's contracted).

NO! You do not need both to get the proper time! The proper time IS exactly the same as the dilated time in SR. That is what the link I showed you says, and that is what the math I posted says. You are WRONG.

but it looked like he was using one set of equations to get time dilatioNo, n and working out the journey time from that and then doing the same thing with length contraction without ever combining the two to get the actual proper time that the journey would take.

You do NOT combine the two to get proper time.

You refuse to accept established theory and facts and continue to believe whatever you want, without any supporting references, only the wrongness inside your own head.

It is a waste of time to try and reason with you.

### #21 A-wal

A-wal

Creating

• Members
• 1324 posts

Posted 22 May 2017 - 04:49 AM

Coordinate time and proper time are certainly NOT the same thing in SR!

Velocity is distance over time. Time dilates reducing the amount of proper time and length in space contracts, again reducing the amount of proper time it takes to make the journey. Of course you need to take both into account to work out the proper time of the journey.

### #22 OceanBreeze

OceanBreeze

Creating

• Moderators
• 1243 posts

Posted 22 May 2017 - 08:04 AM

"So the total proper time for observer B to go from (0,0,0,0) to (5 years, 4.33 light-years, 0, 0) to (10 years, 0, 0, 0) is 5 years. Thus it is shown that the proper time equation incorporates the time dilation effect. In fact, for an object in a SR spacetime traveling with a velocity of v for a time Δ T the proper time interval experienced is

$\Delta \tau ={\sqrt {\Delta T^{2}-(v_{x}\Delta T/c)^{2}-(v_{y}\Delta T/c)^{2}-(v_{z}\Delta T/c)^{2}}}=\Delta T{\sqrt {1-v^{2}/c^{2}}}$

which is the SR time dilation formula"

If you disagree, cite your sources (which you do not have or do not understand) I am done wasting my time with a troll boy.

### #23 A-wal

A-wal

Creating

• Members
• 1324 posts

Posted 22 May 2017 - 10:26 AM

But don’t expect A-wal “Mr special relativity” to admit he is wrong. He never does and he never learns

I gave you the link to follow. If that doesn't convince you, I won't waste any more of my time on you.

You refuse to accept established theory and facts and continue to believe whatever you want, without any supporting references, only the wrongness inside your own head.

It is a waste of time to try and reason with you.

If you disagree, cite your sources (which you do not have or do not understand) I am done wasting my time with a troll boy.

Who's the troll? I've been nothing but polite.

Time dilation and length contraction both contribute to the amount of proper time that elapses on the journey because time dilation slows the traveler's watch and length contraction shortens the distance traveled. I would have thought that was obvious.

Obviously an observer at rest in the starting/destination frame will be length contracted and time dilated from the perspective of the traveler as well. It's the acceleration of the traveler that causes the the difference in proper time to make the journey, not the different inertial frames.

To get the proper time of the journey from the traveler's perspective you need to compare difference of the frame that the traveler starts/finishes in with the one they're in during the journey. If you only take time dilation or only take length contraction into account then of course you'll get the wrong answer.

Edited by A-wal, 22 May 2017 - 10:30 AM.

### #24 mrg

mrg

Questioning

• Members
• 159 posts

Posted 22 May 2017 - 10:57 AM

> Who's the troll? I've been nothing but polite.

The difficulty is that you're full of baloney.

• exchemist likes this

### #25 A-wal

A-wal

Creating

• Members
• 1324 posts

Posted 22 May 2017 - 11:16 AM

> Who's the troll? I've been nothing but polite.

The difficulty is that you're full of baloney.

So you think that proper time and coordinate time are the same thing as well?

Would you mind explaining why a difference in the time measured in the new inertial frame and a difference in the distance traveled in the new inertial frame shouldn't both be taken into account to work out how long the journey would take from the perspective of the traveler?

### #26 mrg

mrg

Questioning

• Members
• 159 posts

Posted 22 May 2017 - 11:22 AM

> Would you mind explaining why ...

I would, but then your brain might explode.

Oh ... too late.

### #27 A-wal

A-wal

Creating

• Members
• 1324 posts

Posted 22 May 2017 - 11:26 AM

In other words you have no clue what you're talking about. That's what I thought.

### #28 mrg

mrg

Questioning

• Members
• 159 posts

Posted 22 May 2017 - 11:32 AM

> In other words you have no clue what you're talking about.

Yeah, yeah -- "and yo' momma."

### #29 A-wal

A-wal

Creating

• Members
• 1324 posts

Posted 22 May 2017 - 11:42 AM

Time dilation shortens the distance in time, causing a shortening of the amount of proper time it takes to make the journey.

Length contraction shortens the distance in space, causing a shortening of the amount of proper time it takes to make the journey.

Both are need to be taken into account in order to work out how much proper time the journey would take for the traveler. Do you disagree?

### #30 mrg

mrg

Questioning

• Members
• 159 posts

Posted 22 May 2017 - 11:45 AM

> Do you disagree?

I'd explain it to you but ... you know the rest.

Bored now.  GAME OVER.

Edited by mrg, 22 May 2017 - 11:47 AM.

### #31 A-wal

A-wal

Creating

• Members
• 1324 posts

Posted 22 May 2017 - 11:51 AM

That you still have nothing you can possibly say without making it glaringly obvious that you don't have the first clue what you're talking about, I see.

### #32 spartan45

spartan45

• Members
• 84 posts

Posted 23 May 2017 - 01:40 PM

No he didn't, he left out length contraction. To get the difference in the amount of proper time it would take to make the journey you need to work out out the difference in coordinate time over the distance in space.

Length contracts by the same amount as time dilates so it should take 270 years proper time.

You were right to highlight who measures the proper time and who measures the proper length as it one of the most important things about special relativity.

Non proper length is measured by the spacecraft, because the spacecraft is measuring events that occur in different places with respect to the spacecraft (the spacecraft could be said to be observing moving planets). In the example this gives the spaceship distance meter calculated reading of 264.23 light years from planet to planet. Non proper length is length contraction, shortening of the distance and is designated L.

Proper time is measured on the spacecraft because its clock is at rest with respect to the spacecraft; a time interval measured by a clock which is at rest relative to the observer. In the example the spacecraft clock gives a journey proper time calculated to be 377.47 years from planet to planet and is designated ∆t0.

The spacecraft instrument dashboard would show total journey distance to be 264.23 light years, total journey time to be 377.47 years at a speed of 0.7c. Put these figures directly into the equation: Time = Distance/Speed    (t=d/s)    t=377.47years, d=264.23 light years, s=0.7c

377.47 years = 264.23 light years/0.7c and it all makes sense.

Proper length is the length (distance) measured by an observer (on the planet in this example) between two points (planets), at rest with respect to them. In the example the proper length planet to planet distance measurement is 370 light years and is designated L0.

Non proper time is measured by an observer on the planet in this example, because the events are occurring in a different place (the spacecraft in this example) and the clock on the planet is not at rest relative to the moving spacecraft. In the example the planet clock gives a journey non proper time calculated to be 528.57 years from planet to planet and is designated ∆t.

The observer on Earth would have the following control panel readings:

Total journey time=528.57years, total journey distance=370 light years, craft speed=0.7c

Put these figures into t=d/s gives 528.57 years=370 lightyears / 0.7c and it all makes sense.

### #33 A-wal

A-wal

Creating

• Members
• 1324 posts

Posted 23 May 2017 - 04:59 PM

Ah thank you. I think I see what you're doing.

I might have some follow up questions when my mind isn't so tired.

### #34 A-wal

A-wal

Creating

• Members
• 1324 posts

Posted 24 May 2017 - 09:20 AM

I was looking at from the perspective of someone in the Earth/destination frame and thinking that time dilation and length contraction are both needed to work out the proper time the journey would take but I suppose looking at it from the accelerator's perspective, what they experience is just a shortening of distance in the direction of acceleration so you can work out the distance in proper time just from that.

Acceleration is definitely the most awkward part of SR. Just to see if I'm picturing this right, if you think about what the accelerator sees when looking a clock on Earth (after taking the delay of the journey time of the light into account), the clock would move slowly during the journey until it was 151 years behind once the accelerator reaches the destination, and then (if we use instant acceleration) instantly jump forward 302 years so it's 151 years ahead of the accelerator's own clock.

Then when the accelerator makes the return journey, Earths clock runs slow until the two are in perfect sync when the accelerator reaches Earth but then the Earth clock jumps forward another 302 years when the accelerator accelerates back into Earth's frame?