Clocks in space

[MiseryStreak]

OK, I've found the answer, there is a transition point, at round 5 times the radius of the Earth where the velocity effects and gravitational effects cancel out, graph here:

http://www.wolframalpha.com/input/?i=plot+sqrt(1-(...

From yuiop's post here:
http://www.physicsforums.com/showthread.php?t=4743...

So, if your geosynchronous space station is within approx. 5r (Earth Radii) then its clock will tick faster relative to the stationary one. If it is orbiting at greater than approx. 5r then its clock will tick slower.

[Piersman2]

Does this explain why my flight back from Dusseldorf last week landed only 5 minutes after it took off? Despite the flight seeming to last about an hour?

[bulldog5046]

wow, what a fascinating topic!

Something i've never heard of before and a i think i've figured out the logic but would someone mind giving a breif explination as to why this happens?

I'd rather not make myself sound like a complete ass-hat trying to explain the nonsense in my head

[Mr E]

bulldog5046 said:

Something i've never heard of before and a i think i've figured out the logic but would someone mind giving a breif explination as to why this happens?

Such an explanation would not be brief....

[MiseryStreak]

bulldog5046 said:

Would someone mind giving a brief explanation as to why this happens?

Which bit? Time dilation, Special Relativity, General Relativity, or a more particular bit of the stuff discussed so far?

Way too much to answer succinctly here and I would be plagiarising the relevant Wikipedia articles for expedience.

Better to read this first ( http://en.wikipedia.org/wiki/General_relativity ) and follow the hyperlinks on a very long journey!

In a sentence (Where's Gene when you need him?):

Movement in space (up/down/left/right/forwards/backwards) reduces movement in time, so the faster moving clock on the space station experiences less time than the stationary one, so it is slow when they are compared again after its space journey.




P.S. I'm sorry I corrected the typos in your quote, I've got a touch of OCD...

[mattnunn]

Has Gene not been in to explain?

Check out the "Time" thread...

[Gene Vincent]

MS has encompassed it really.

Your existence is an energy quotient, pure and simple and just sitting still, means all your energy is 'spent' just travelling through your local timeframe (in fact every atom of you has its own time frame but we can cope with that and has no significance, just accuracy) so time passes at the speed you have come to expect.

As your own energy quotient is acted upon by other energy moving you through space, less of it is available for your own frame to allow time to pass normally, so it slows, the faster you go the slower time passes as a result of this 'accounting' for your own energy quotient.

Gravity or rather the local energy depletion effect of gravity does the same but in reverse, so as you rise away from the centre of this planet time travels faster, so if you descend deep into this planet (ignoring the heat) time will slow.

[Use Psychology]

awesome, so if i spin round and round in my office chair all day at work, whilst sticking my legs out, my feet will end up significantly younger than my head.

[Gene Vincent]

Use Psychology said:

awesome, so if i spin round and round in my office chair all day at work, whilst sticking my legs out, my feet will end up significantly younger than my head.

Yep. maybe that's why it's so much fun, you have happy, younger feet!

[bulldog5046]

Gene Vincent said:

MS has encompassed it really.

Your existence is an energy quotient, pure and simple and just sitting still, means all your energy is 'spent' just travelling through your local timeframe (in fact every atom of you has its own time frame but we can cope with that and has no significance, just accuracy) so time passes at the speed you have come to expect.

As your own energy quotient is acted upon by other energy moving you through space, less of it is available for your own frame to allow time to pass normally, so it slows, the faster you go the slower time passes as a result of this 'accounting' for your own energy quotient.

Gravity or rather the local energy depletion effect of gravity does the same but in reverse, so as you rise away from the centre of this planet time travels faster, so if you descend deep into this planet (ignoring the heat) time will slow.

I think i'm following.

I believe the part i was enquiring about was time dilation.

My logic was along the lines of, the faster you go, the more time slows down? i guess, until the speed of light where time would stop?

Does Brian Cox cover any of this anywhere? i find him very easy to watch

[Gene Vincent]

bulldog5046 said:

I think i'm following.

I believe the part i was enquiring about was time dilation.

My logic was along the lines of, the faster you go, the more time slows down? i guess, until the speed of light where time would stop?

Does Brian Cox cover any of this anywhere? i find him very easy to watch

http://www.pistonheads.com/gassing/topic.asp?h=0&f=219&t=1184024&mid=240344&nmt=Time%2E

The first post.

[Pvapour]

Gene Vincent said:

bulldog5046 said:

I think i'm following.

I believe the part i was enquiring about was time dilation.

My logic was along the lines of, the faster you go, the more time slows down? i guess, until the speed of light where time would stop?

Does Brian Cox cover any of this anywhere? i find him very easy to watch

http://www.pistonheads.com/gassing/topic.asp?h=0&f=219&t=1184024&mid=240344&nmt=Time%2E

The first post.

& then any faster would theoretically mean you would travel backwards through time, wasn't that Heinsteins theory or Jules vern, mad doc??? sumit like that

thanks for heads up on the book

[bulldog5046]

Gene Vincent said:

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

The first post.

doesnt that contradict time dilation though?

I guess what i should of said is to the observer time would appear to stop, and to the person travelling at the speed of light, everything else appears to stop? maybe?

[V8LM]

Question I had about the two clocks; one in the space craft/airplane and the other on the ground, that I asked my A-level physics teacher who couldn't answer - which one is moving? When the pilot of the airplane is asked by the crew on the ground which clock is running slower than the other, what does he say?

[FarmyardPants]

V8LM said:

Question I had about the two clocks; one in the space craft/airplane and the other on the ground, that I asked my A-level physics teacher who couldn't answer - which one is moving? When the pilot of the airplane is asked by the crew on the ground which clock is running slower than the other, what does he say?

It's been a while since I was interested in this stuff, so happy to be corrected, but this question is aka the twins paradox, where one twin goes off on a journey and comes back younger than the other, but velocities being relative you should be able to define the travelling twin as the stationary one in which case the other one should be younger (I think that's how it goes).

The difference is that one twin experiences the force of acceleration and the other doesn't. When you accelerate you move from one inertial frame to another. The speed of light was X before you set off, and now that you've accelerated to a speed of Y, the speed of light is still X in the frame you occupy (not X+Y or whatever). Which doesn't seem to add up, as a light beam sets off at X and reaches you at X and yet you are moving relative to your starting point - did the speed of light change? By accelerating, you have in a sense dragged along your own local environment with you, and it is not the speed of light that changed, it is the passage of time as measured from one frame observing the other.

To answer your question, and to make it more interesting we can assume that both the pilot and the guy on the ground are in windowless capsules, the pilot would say "did you feel the force of any acceleration?" If the reply is yes, then his clock will show less elapsed time when he returns to the original frame, otherwise the pilot's will. Whilst there is no such thing as absolute velocity, you can measure acceleration quite easily, and hence derive a relative velocity without any external frame of reference (say, by looking out of the window )

[Pints]

Gene Vincent said:

MS has encompassed it really.

Your existence is an energy quotient, pure and simple and just sitting still, means all your energy is 'spent' just travelling through your local timeframe (in fact every atom of you has its own time frame but we can cope with that and has no significance, just accuracy) so time passes at the speed you have come to expect.

As your own energy quotient is acted upon by other energy moving you through space, less of it is available for your own frame to allow time to pass normally, so it slows, the faster you go the slower time passes as a result of this 'accounting' for your own energy quotient.

Gravity or rather the local energy depletion effect of gravity does the same but in reverse, so as you rise away from the centre of this planet time travels faster, so if you descend deep into this planet (ignoring the heat) time will slow.

But why is there such a marked difference when traveling west vs. east?

I don't see how direction of travel can make a difference, given your (rather good) explanation.

[MiseryStreak]

Pints said:

Gene Vincent said:

MS has encompassed it really.

Your existence is an energy quotient, pure and simple and just sitting still, means all your energy is 'spent' just travelling through your local timeframe (in fact every atom of you has its own time frame but we can cope with that and has no significance, just accuracy) so time passes at the speed you have come to expect.

As your own energy quotient is acted upon by other energy moving you through space, less of it is available for your own frame to allow time to pass normally, so it slows, the faster you go the slower time passes as a result of this 'accounting' for your own energy quotient.

Gravity or rather the local energy depletion effect of gravity does the same but in reverse, so as you rise away from the centre of this planet time travels faster, so if you descend deep into this planet (ignoring the heat) time will slow.

But why is there such a marked difference when traveling west vs. east?

I don't see how direction of travel can make a difference, given your (rather good) explanation.

When you travel East you are travelling with the Earth's rotation (anti-clockwise when viewed from the North Pole or 'top') so your velocity is added to the Earth's rotational velocity (approx. 1,000mph at the equator at sea level).
When you travel West you are travelling against the Earth's rotation so your velocity is subtracted from the Earth's rotational velocity.
So if you are in an aeroplane at the equator and travel at (slightly more than as you are at altitude) 1,000mph in a Westbound direction, your velocity is effectively zero RELATIVE to a stationary point on the equator. Therefore, if you have an accurate clock with you, as your velocity is 1,000mph slower than the stationary clock you left at the airport, you will have experienced more time, and when you return after your circumnavigation, the stationary clock will be slow, or behind in its reading.

[Pints]

MiseryStreak said:

When you travel East you are travelling with the Earth's rotation (anti-clockwise when viewed from the North Pole or 'top') so your velocity is added to the Earth's rotational velocity (approx. 1,000mph at the equator at sea level).
When you travel West you are travelling against the Earth's rotation so your velocity is subtracted from the Earth's rotational velocity.
So if you are in an aeroplane at the equator and travel at (slightly more than as you are at altitude) 1,000mph in a Westbound direction, your velocity is effectively zero RELATIVE to a stationary point on the equator. Therefore, if you have an accurate clock with you, as your velocity is 1,000mph slower than the stationary clock you left at the airport, you will have experienced more time, and when you return after your circumnavigation, the stationary clock will be slow, or behind in its reading.

But that's not related to the energy spent travelling in either direction. Do we use more energy when travelling West versus East?

[Alfanatic]

Pints said:

MiseryStreak said:

When you travel East you are travelling with the Earth's rotation (anti-clockwise when viewed from the North Pole or 'top') so your velocity is added to the Earth's rotational velocity (approx. 1,000mph at the equator at sea level).
When you travel West you are travelling against the Earth's rotation so your velocity is subtracted from the Earth's rotational velocity.
So if you are in an aeroplane at the equator and travel at (slightly more than as you are at altitude) 1,000mph in a Westbound direction, your velocity is effectively zero RELATIVE to a stationary point on the equator. Therefore, if you have an accurate clock with you, as your velocity is 1,000mph slower than the stationary clock you left at the airport, you will have experienced more time, and when you return after your circumnavigation, the stationary clock will be slow, or behind in its reading.

But that's not related to the energy spent travelling in either direction. Do we use more energy when travelling West versus East?

It's not 1000mph slower than the clock. It's all relative to the observers, in this case they are you, and the clock at the airport. The clock at the airport witnessed you accelerate to the west. You witnessed the airport clock accelerate to the east. Only one of the two observers expended energy to make this happen. So it doesn't matter if you go around the world. As far as I can tell.

EDIT: Sorry, just seen the evidence on pg 1 to the contrary, so I dump myself in the "I don't get it" camp too.

Edited by Alfanatic on Thursday 23 August 13:50

EDIT 2: Is it centripetal force due to gravity? The airport clock isn't stationary but is in fact constantly changing its direction of acceleration while it orbits the centre of gravity. Meanwhile the plane flying west completes fewer radians than the clock, so in that way experiences less acceleration? If you plotted both paths in a plan view the plane took a straight line point to the end, but the clock did a big S? Bear with me, I a burdened with having to try to understand things in Alfanatic terms

Edited by Alfanatic on Thursday 23 August 14:26

[MiseryStreak]

Pints said:

MiseryStreak said:

When you travel East you are travelling with the Earth's rotation (anti-clockwise when viewed from the North Pole or 'top') so your velocity is added to the Earth's rotational velocity (approx. 1,000mph at the equator at sea level).
When you travel West you are travelling against the Earth's rotation so your velocity is subtracted from the Earth's rotational velocity.
So if you are in an aeroplane at the equator and travel at (slightly more than as you are at altitude) 1,000mph in a Westbound direction, your velocity is effectively zero RELATIVE to a stationary point on the equator. Therefore, if you have an accurate clock with you, as your velocity is 1,000mph slower than the stationary clock you left at the airport, you will have experienced more time, and when you return after your circumnavigation, the stationary clock will be slow, or behind in its reading.

But that's not related to the energy spent travelling in either direction. Do we use more energy when travelling West versus East?

I'm sorry I answered it on my terms. We don't use more energy as such (not in terms of jet fuel) as we are already in motion just sitting on the surface of the Earth, relative to the centre of mass. But ignore the gravity for the moment, as I was talking about the Relative Velocity time dilation experienced by the planes. Let's leave Gravitational time dilation out of this by imagining that the aeroplane is actually cruising at 5,000m and the stationary airport is at 5,000m altitude. The plane takes off by dropping off the end of a runway (no, not a conveyor belt runway!) and remains level throughout its circumnavigation, so the gravity is the same for the airport and both planes.

Now, let's negate the Earth's velocity on its orbit around the sun (which is approx. 67,000mph). We can do this because this velocity is existent on the Earth, the airport and both aeroplanes in the same manner. So in terms of this velocity everything is in the same inertial frame. It's more complex than this but no matter.

So the airport clock is travelling at 1,000mph compared with the North Pole, which is just rotating 360 degrees every 24 hours. A spot on the ice 1m away from the North Pole is travelling at (2 x Pi x 1) = 6.28m per day or 0.0000002m/s. (At 52 degrees North latitude here in Brighton, we are travelling at 615mph - Just multiply the equatorial speed by the Cosine of your latitude).

So two more clocks take off in opposite directions, one in an Eastbound plane, another in a Westbound plane. Both planes travelling at 1,000mph. The Eastbound plane is travelling at 2,000mph compared with the North Pole, the Westbound plane is travelling at 0mph compared with the North Pole (Hey, this is a similar problem to the conveyor belt runway!).

So, in relativistic terms, the Westbound plane is travelling at 0c, the airport is travelling at 0.0000015c and the Eastbound plane is travelling at 0.0000030c.

Therefore:
The Westbound plane clock has travelled the slowest in space (space as in the spatial dimensions!), so the fastest in time and should be the fastest clock, i.e. ahead in time.
The airport clock has travelled the second fastest in space and so should be slower than the Westbound clock but faster than the Eastbound clock.
The Eastbound plane clock has travelled the fastest in space, so the slowest in time and should be the slowest clock, i.e. behind in time.

And experimentally they were this way, in the Hafele-Keating experiment, compared with the 'stationary' clock, the Eastward plane lost 59 microseconds and the Westward plane gained 273 microseconds.

It only seems counterintuitive at first because we think of the control clock (the airport one) as not moving. But we're all well aware that we're moving all the time and when we fly (sorry, flew) by Concord to the States, we would arrive before we left, as we have flown against and beaten the Earth's rotation, so the local time and the sun is further back than when we left. True time travel!