Friday conumdrum with DDD - The twin paradox, help!

DonDaddyD

OK so I took public transport todayand was reading the Metro.

There was this interesting piece about the 'twin paradox' and time being relative to speed.

Besically it went on to explain why a person moving away from Earth at 80percent of the speed of light will return younger (than someone on Earth, that is exactly the same age as them, a twin for example).

I actually can't comprehend the mechanics of this and need it explained (you can draw on references or examples that I can understand like comic books and Star Trek).

In my mind if you move away from Earth at any speed below the speed of light* you just get to the destination quicker, your body doesn't stop ageing normally relative to the entire Universe and your Omega space watch doesn't suddenly move more quickly. You stop turn around and when you return (assuming travelling at the same speed), everything is relative and all that happens is people on Earth say "bloody hell that was quick". - This may go against Einstein's theory of relativity.

I'm to understand that the theory works on the basis that in this instance people on Earth are subject to their own passage of time ( a bubble which is moving more quickly) and the person on the ship is subject to their own (which is moving more slowly than Earth's despite them travelling faster). But time is a constant and the only variable is our perception of its passage the physical implications shouldn't change. If it takes 50yrs to get to A (no matter how quickly) 50yrs will have passed as a whole - except for things travelling multiple times faster than light.

Help!

*Because at the speed of light things get screwy - like if you and a beam/wave of light - say daylight - travel from the sun to the Earth and you get their before it, have you beaten time/gone back in time?

jonginge

If it takes 50yrs to get to A (no matter how quickly) 50yrs will have passed as a whole - except for things travelling multiple times faster than light.

50 years of whose time? It's a personal thing, which is the point of the twins paradox


Edit: things travelling multiple times the speed of light? Not outside of sci-fi. (Let's not go to Bell's theorem)

asprilla

http://www.bbc.co.uk/iplayer/episode/b0 ... Episode_1/

Marvel as they demonstrate the theory of relativity by flying an atomic clock around the world.

OK, it's not 80% of the speed of light, but any difference in speed makes a difference; that's why cycling makes you live longer.

GPS sats need constant clock corrections because they are orbiting at about 18,000mph (or something like that, I forget the exact figure).

jonginge

Muon decay half-life was a good confirmation of time dilation in special relativity: http://en.wikipedia.org/wiki/Time_dilation

wgwarburton

Hi,
Let me see if I can oversimplify without actuallly being incorrect :-)

As you approach the speed of light, time slows down. So if you put a clock in a box and send it on an out & back trip at that sort of speed, less time will have passed inside the box than will have passed here on earth during the period it was away.
The perception will be the same but the actuality will be different, time being relative to the observer. You need to accept that time can be elastic to grasp it, I think.

Cheers,
W.

asprilla

WGWarburton wrote:

Hi,
Let me see if I can oversimplify without actuallly being incorrect :-)

As you approach the speed of light, time slows down.

The effect is caused by any relative change of speed or local gravitational effects, it's just that we'd have to get close to the speed of like in order for the effects to be visable to the human eye.

DonDaddyD

JonGinge wrote:

If it takes 50yrs to get to A (no matter how quickly) 50yrs will have passed as a whole - except for things travelling multiple times faster than light.

50 years of whose time? It's a personal thing, which is the point of the twins paradox


Edit: things travelling multiple times the speed of light? Not outside of sci-fi. (Let's not go to Bell's theorem)

My understanding:

Time is a Universal constant, 50yrs here is 50yrs there and things that age slowly over 50yrs will do so. 50yrs moving at close to the speed of light will still mean that the human body ages 50yrs relative to the a human body ageing 50yrs that isn't moving close to the speed of light, surely? No?

The only way to not be subject too time is to remove the physical body from it, which is to move faster than light because light and time are relative (I feel I'm getting into time travel here). Basically all things within the Universe are subject to its rules/physics.

I'm cracking this, I tells you!

jonginge

DonDaddyD wrote:

JonGinge wrote:

If it takes 50yrs to get to A (no matter how quickly) 50yrs will have passed as a whole - except for things travelling multiple times faster than light.

50 years of whose time? It's a personal thing, which is the point of the twins paradox


Edit: things travelling multiple times the speed of light? Not outside of sci-fi. (Let's not go to Bell's theorem)

My understanding:

Time is a Universal constant, 50yrs here is 50yrs there and things that age slowly over 50yrs will do so. 50yrs moving at close to the speed of light will still mean that the human body ages 50yrs relative to the a human body ageing 50yrs that isn't moving close to the speed of light, surely? No?

The only way to not be subject too time is to remove the physical body from it, which is to move faster than light because light and time are relative (I feel I'm getting into time travel here). Basically all things within the Universe are subject to its rules/physics.

I'm cracking this, I tells you!

No

DonDaddyD

WGWarburton wrote:

Hi,
Let me see if I can oversimplify without actuallly being incorrect :-)

As you approach the speed of light, time slows down. So if you put a clock in a box and send it on an out & back trip at that sort of speed, less time will have passed inside the box than will have passed here on earth during the period it was away.
The perception will be the same but the actuality will be different, time being relative to the observer. You need to accept that time can be elastic to grasp it, I think.

Cheers,
W.

The passage of time flows differently at different points. So its not a straight string but a shape with corners and each corner the speed at which time flows is different to the straight parts of the string. We can bend the string to create our own corners. I kinda get that.

OK so the clock. The clock is in a box its ticking relative to the outside World. It's sent around the Earth at just below the speed of light. It get back the clock less time has passed for the clock than the outside World. Becuase time flows more slowly as it approaches the speed of light....

I think the question is then, why does time move more slowly the faster you approach the speed of light?

DonDaddyD

JonGinge wrote:

DonDaddyD wrote:

JonGinge wrote:

If it takes 50yrs to get to A (no matter how quickly) 50yrs will have passed as a whole - except for things travelling multiple times faster than light.

50 years of whose time? It's a personal thing, which is the point of the twins paradox


Edit: things travelling multiple times the speed of light? Not outside of sci-fi. (Let's not go to Bell's theorem)

My understanding:

Time is a Universal constant, 50yrs here is 50yrs there and things that age slowly over 50yrs will do so. 50yrs moving at close to the speed of light will still mean that the human body ages 50yrs relative to the a human body ageing 50yrs that isn't moving close to the speed of light, surely? No?

The only way to not be subject too time is to remove the physical body from it, which is to move faster than light because light and time are relative (I feel I'm getting into time travel here). Basically all things within the Universe are subject to its rules/physics.

I'm cracking this, I tells you!

No

OK but why is time not a universal constant. What would you say are the Universal constants? I always understood them to be time light/dark and gravity. Which in turn shapes the one major rule that all enegy is transferable...

jonginge

DonDaddyD wrote:

JonGinge wrote:

DonDaddyD wrote:

JonGinge wrote:

If it takes 50yrs to get to A (no matter how quickly) 50yrs will have passed as a whole - except for things travelling multiple times faster than light.

50 years of whose time? It's a personal thing, which is the point of the twins paradox


Edit: things travelling multiple times the speed of light? Not outside of sci-fi. (Let's not go to Bell's theorem)

My understanding:

Time is a Universal constant, 50yrs here is 50yrs there and things that age slowly over 50yrs will do so. 50yrs moving at close to the speed of light will still mean that the human body ages 50yrs relative to the a human body ageing 50yrs that isn't moving close to the speed of light, surely? No?

The only way to not be subject too time is to remove the physical body from it, which is to move faster than light because light and time are relative (I feel I'm getting into time travel here). Basically all things within the Universe are subject to its rules/physics.

I'm cracking this, I tells you!

No

OK but why is time not a universal constant. What would you say are the Universal constants? I always understood them to be time light/dark and gravity. Which in turn shapes the one major rule that all enegy is transferable...

Time is personal. Speed of light is a constant everywhere, in every inertial reference frame.

Read the "Simple inference of time dilation due to relative velocity" section of the wiki page link I posted for an answer to the last question you posed in response to Buns

asprilla

Well gravity isn't constant because it varies according to distance and mass. The speed of light isn't constant either; the speed of light in a vacuum is but it moves slower though a medium such as glass or water.

PBo

The clue is in the word "relativity". Time is constant in your own frame of reference, but your are comparing two frames of reference which are at different speeds relative to each other. The stay at home twin's interpretation is that the space ship twin is moving relative to him. But it is equally valid to say that the twin and the space ship- from their own frame of reference- are still, but the earth and the twin travelled away ( in the opposite direction) before coming back. So two frames of reference. Time is constant for each, only within that frame of reference. The relative "speed" of each clock depends on the velocity difference of the two frames of reference. The nearer that velocity is to the speed of light, the bigger the difference in clock speed, that one twin sees when looking at the other. Their own clock- too themselves- still seems constant.

jonginge

Asprilla wrote:

Well gravity isn't constant because it varies according to distance and mass. The speed of light isn't constant either; the speed of light in a vacuum is but it moves slower though a medium such as glass or water.

Yes, depends on magnetic permeability and electric permittivity of the medium. Leads to interesting effects like Cerenkov radiation...

Kieran_Burns

JonGinge wrote:

Asprilla wrote:

Well gravity isn't constant because it varies according to distance and mass. The speed of light isn't constant either; the speed of light in a vacuum is but it moves slower though a medium such as glass or water.

Yes, depends on magnetic permeability and electric permittivity of the medium. Leads to interesting effects like Cerenkov radiation...

and rainbows

jonginge

Kieran_Burns wrote:

JonGinge wrote:

Asprilla wrote:

Well gravity isn't constant because it varies according to distance and mass. The speed of light isn't constant either; the speed of light in a vacuum is but it moves slower though a medium such as glass or water.

Yes, depends on magnetic permeability and electric permittivity of the medium. Leads to interesting effects like Cerenkov radiation...

and rainbows

Indeed.

DonDaddyD

OK I'm readingup on this time thing.


Other issue, Universal contansts in the fact that there is no negative concept. I always thought that:

Light/Dark is a constant in the sense that it is a form of matter/energy, which in itself is a constant

Time - There is no negative concept of time I.e. it doesn't travel backwards.

Gravity - whether it is 0 or 100 exists and there is no negative

Please shoot these down, I'm in learning mood. None of the DDDness.

g00se

OK - this is a good description of what you're talking about. I heard it a few months ago.

Time is the forth dimension and we're travelling through it. We can't 'see' the forth dimension but we experience travelling through it as time.

To help visualise it, remove our normal third dimension and think of us living on a two-dimensional flat plane (a piece of paper). Now, time is us moving up...

Now - this is the good bit...

EVERYTHING is travelling at the speed of light. Generally, we're travelling through the forth dimension at that speed - so we're travelling through time at the speed of light.

Now, nothing can go faster that the speed of light. So if we move somewhere in our three dimensions, then we are not going quite as fast through the forth dimension. But with the speed of light so fast, our relative slowdown in the forth dimension is not noticeable.

Think of the 'remove the third dimension' example. if everything is flying up at the same speed (going through time) - if something veers to the left but stays at the same speed, then it won't be rising as fast as everything else.

As I said, this isn't noticeable at 'normal' speeds due to how bloody fast the speed of light is - but if something's speed approaches that order of magnitude going sideways, progress through time is noticeably slower (from the view of others).

Phew....!

spen666

DonDaddyD wrote:

....
I actually comprehend the mechanics of this and need it explained (you can draw on references or examples that I can understand like comic books and Star Trek). ....

I may be stupid DDD, but if you comprehend it, why do you need someone to explain it to you now?

DonDaddyD

Sorry typo.

So we are travelling through time.

The closer we get to the speed of light the faster we travel through time.

Is distance a factor? Or is it a metaphysical concept in that distance doesn't have to be actually travelled the movement is time itself?

Are light, time and speed all relative?

mkirby

g00se wrote:

Now, nothing can go faster that the speed of light.

Thats not strictly true, light itself can go faster then c when passed through the correct medium. You cannot accelerate a body with mass up to the speed of light. If you want an object with mass to be at c or above then it must come into existance at that speed (which is never going to happen). However it is theoretically posible to have some form of massless particle that cannot carry information be born at a speed greater than c. No idea if any have been found but i remember reading about them in new scientist.

Then there is also quantum coupling but that will really bend your brain.

neiltb

DonDaddyD wrote:

Is distance a factor? Or is it a metaphysical concept in that distance doesn't have to be actually travelled the movement is time itself?

distance is just time at a speed, so it's there already.

As for the non mass can exceed c, never got that. if t cars approach each other, each travelling at 30m/s, then closing speed is 60 m/s. In the LHC they accelerate particles close to c (?) say 0.8c if I had one going the same speed the other way what gives?

desweller

It's worth point out that there are probably only a few thousand people on the planet who genuinely understand Einstein's Special and General Theories of Relativity. So, while lots of people might be able to quote the predicted effects in layman's terms (as they have been frequently written about), very few will actually be able to help you understand why it works.

You can try reading the Wikipedia articles(Special and General), as they are written in clear language, but the concepts are not simple and there is not really a way of simplifying them. They do not correspond with our everyday observed examples of Newtonian physics, so you have to be prepared to accept some pretty counter-intuitive things.

If you're not a particle physicist by trade, then chances are you probably won't understand. I'm an engineer, and I am used to using higher mathematics to analyse problems, but this one is beyond me.

Kieran_Burns

So we are travelling through time.

No. We exist in time.

The closer we get to the speed of light the faster we travel through time.

With the limitations of the above: no - it's the other way around: time appears to pass at the same rate to us, but more slowly to others

Is distance a factor? Or is it a metaphysical concept in that distance doesn't have to be actually travelled the movement is time itself?

No. You have to start looknig at the concept of spacetime (the old rubber sheet analogy)

(as alluded to above) You need to see time as a dimension, not as a duration. As an object you can be be measured in 3 dimensions, height, breadth, depth but you can also be measured in time. You need to see yourself as an event within spacetime, not as an object in space

g00se

DonDaddyD wrote:

Sorry typo.
The closer we get to the speed of light the faster we travel through time.

Nope - the opposite - the faster we go (in our three physical dimensions), the 'slower' we go through time.

DonDaddyD wrote:

Is distance a factor? Or is it a metaphysical concept in that distance doesn't have to be actually travelled the movement is time itself?

Only in that it is a measure of our movement in our three dimensions. As we travel through time (at the speed of light) we don't travel any distance as we understand it in three dimensions (assuming we are standing still within those three dimensions).

DonDaddyD

Des,

I'll have you know I have over 5000 comic books, where I specialise in cosmic storylines and clocked up several yrs arguing about incontinuity physics on comic websites. I've also built a scaled model of the Star Ship Enterprise A and D as well as a Ferengi Maurader and a Klingon Bird of Prey (lovel ship). I have a full understanding of warp drive, hyperdrive, quantum slipstream and transwarp. I even drew a blue print for a basic matter/antimatter reactor in my early teens.

I'm well versed on the concept of paradoxes, big bangs, particle physics and the transferance of energies. I've dabbled in the mystic arts, astrology, mythology and genetics.

And I'm a Lt Commnder grade 8 on Star Trek Online.

I'm sure I'l crack this Einstein thing.

So OK maybe a little DDD.

But seriously Des, thanks for the links and the perspective.

g00se

Kieran_Burns wrote:

You need to see time as a dimension, not as a duration. As an object you can be be measured in 3 dimensions, height, breadth, depth but you can also be measured in time. You need to see yourself as an event within spacetime, not as an object in space

Now, they gets into the funky event-time thing. As we 'pass' through time as a dimension, it

would suggest that our future is pre-ordained - like walking down a road, you know where you are going to end up.

A theory is (as I understand it as a layman) that there are an infinite number of universes to cover every possibly outcome of every possible action. So (bringing it back to commuting) when you get to a red light, there is a universe where you stop, and a universe where you jump it. And if you jump it, there is a universe where you get across and a universe where you get hit by a car etc... Each of these possible events has a probability of occurring so our travel through time is a probability-based journey through multiple universes.



Think of space-time as a flip book. Each page is our three dimensions (two dimensional in this case so we can see time). Close the book and the width of the book is time. You can flick the pages and see the universe move through time.

But for every possibly event, there is another book - and we jump between books as every indeterminate thing occurs.

Kieran_Burns

Goose - you're referring to wave function collapsing upon the interaction of an individual on the Universe.

I see it as the other way 'round from your supposition: the infinite number of possible Universes collapsing into the one actual one that becomes reality when the action is completed. Infinite possibiliites in life, one reality: whatever you make of it.

Kieran_Burns

At this point DDD will leap in with IDIC 8)

mr_poll

"Time?
Time is an illusion of the mind - lunchtime doubly so".

- Ford Prefect

Doesn't help matters I just love the quote.

DonDaddyD

IDIC?