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Author Topic: Does time dilation alter the rate at which a body accelerates to light-speed?  (Read 8853 times)

Offline ukmicky

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When mass is accelerated time dilation occurs in regards to the object thatís accelerating
Causing time to slow down for the object thatís accelerating compared to everything else in the universe [8D].

So if i wanted to work out how much time it would take me and my rocket to accelerate to a specific speed nearing the speed of light in a vacuum, would the effect of time dilation effect the answer regarding how long it would take?
And if so does that mean the more i accelerated and the faster i went the greater time dilation would occur so the longer it would take me causing a never ending fight between acceleration and time.

Iím slowly coming to terms with time dilation but not quite there yet :)
« Last Edit: 13/04/2012 20:44:51 by chris »


 

Offline DoctorBeaver

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Re: time dilation
« Reply #1 on: 03/06/2005 13:33:01 »
To the object being accelerated time passes at the same speed as when that object was at rest. It is an observer outside of the object's frame of reference who notices the dilation. Therefore if you are on a spaceship that accelerates to near C, then returns to your point of origin 5 years later by your reckoning, to someone who stayed at the point of origin it would have been much longer than 5 years. So, in your calculation you need take no notice of time dilation.
If, however, you wanted to do the calculation from the perspective of someone remaining at the point of departure, then yes you would have to take it into account.
 

Offline ukmicky

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Re: time dilation
« Reply #2 on: 04/06/2005 01:44:08 »
Right I enter a competition to be the first man to travel at 250.000 mph over a prescribed distance.
Now as Arizona isnít big enough for my attempt I have no alternative but to do it in a rocket ship up in space
Iíve got to do a round trip of 4 million miles with no stopping or slowing and as Iím traveling at 250.000 mph (easy one to calculate) we on earth have worked out that my ship should cross the Finish line within 16 hours and in doing so I will win the cup for being the fastest man.
So I say goodbye to the scantily clad women and the worlds press assembled for my departure, Jump into my rocket where I accelerate to the above speed and cross the start line as I begin my journey
 
Now for me and my rocket after 16 hours of traveling I cross the finish line and end my journey.
 Now for me its taken 16 hours as first worked out. But for the people I left back on earth due to time dilation its taken say 20 hours meaning Iíve missed my welcome home party and in their perspective have failed in my attempt because I didnít return within 16 hours meaning my ship must have been  traveling less than 250,000 mph .

Now apart from the man who waited,  Telling me that life's a bitch
Would that be a good description of time dilation?
 

Offline gsmollin

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Re: time dilation
« Reply #3 on: 04/06/2005 05:47:34 »
Not quite. The observers will see you go around the course of 4,000,000 miles at 250,000 mph and so take 16 hours to complete. You will see the course length shortened by the Lorentz length contraction, and measure less than 4,000,000 miles to travel, so you will measure less than 16 hours to complete the course. Incidently, the observers will see your spaceship foreshortened by the Lorentz length contraction.
« Last Edit: 04/06/2005 05:49:05 by gsmollin »
 

Offline ukmicky

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Re: time dilation
« Reply #4 on: 04/06/2005 14:51:57 »
maybe one day i'll get there. back to my studies.
this subject can be soooooooooooo confusing
« Last Edit: 04/06/2005 15:13:05 by ukmicky »
 

Offline ukmicky

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Re: time dilation
« Reply #5 on: 05/06/2005 01:07:32 »
gs and doc thankyou for your imput but im confused
the doc above says
It is an observer outside of the object's frame of reference who notices the dilation.
but gs you say
The observers will see you go around the course of 4,000,000 miles at 250,000 mph and so take 16 hours to complete. so  going buy that statememt the observers are not seeing any dilation.
i know its down to my ignorance and im not understanding something quite right
so arrrrrrrrrrrrghhhhhhhhhh
how about an easy explanation of how it all works which includes Lorentz length contraction
 

Offline DoctorBeaver

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Re: time dilation
« Reply #6 on: 05/06/2005 14:22:06 »
Hey - what do I know? I'm a psychologist!
Both GS & I are correct. Maybe I wasn't very clear with what I said.
Say you sychronise watches with someone who will remain at home & you set off on your journey. To you it will have taken 16 hours for you to return & it will also be 16 hours for the person who remained at home. But when you compare watches, yours will be behind the person who was stationary.
 

Offline gsmollin

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Re: time dilation
« Reply #7 on: 05/06/2005 16:07:45 »
This problem is easiest to explain just the way I explained it. The course is measured by observers at rest to the course. It is 4 million miles long. You are moving at 1/4 million mph as measured by the observers at rest, so you take 16 hours to complete the course. What could be simpler?

Now you, inside the spaceship, are moving during the race, so your time is dilated. You take less time to complete the course than the observers at rest will observe. When you exit the spaceship, your watch is behind the obervers'.

During the race, you see the length of the course shortened by the Lorentz length contraction. This has to coincide with the time dilation, because you are going to finish sooner than the observers at rest measure. In fact, the time dilation formula in SR is derived from the Lorentz length contraction formula, so they are different ways of saying the same thing.
 

Offline DoctorBeaver

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Re: time dilation
« Reply #8 on: 05/06/2005 17:26:08 »
Mind you, at only 250,000mph there won't be much dilation
 

Offline chimera

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Re: time dilation
« Reply #9 on: 05/06/2005 20:29:57 »
Clocks also vary with the height you hang them, strangely.

The living are the dead on holiday.  -- Maurice de Maeterlinck (1862-1949)
 

Offline DoctorBeaver

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Re: time dilation
« Reply #10 on: 05/06/2005 21:28:31 »
quote:
Clocks also vary with the height you hang them, strangely.

Of course they do. Gravity affect time
 

Offline chimera

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Re: time dilation
« Reply #11 on: 05/06/2005 21:54:04 »
Also has to do with the energy you 'store' in the clock by elevating it, I read.

The living are the dead on holiday.  -- Maurice de Maeterlinck (1862-1949)
 

Offline DoctorBeaver

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Re: time dilation
« Reply #12 on: 05/06/2005 22:05:26 »
Did you also know that a kettle of hot water weighs less than a kettle with the same amount of cold water?
 

Offline chimera

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Re: time dilation
« Reply #13 on: 06/06/2005 09:56:57 »
Water expands when it's hot, so that would figure.

The clock story is different, though, and has to do with speed ofcourse. One reason is that if you hang a clock on top of the Empire State building, it will run slower than one on the ground, since it describes a bigger circle caused by the earth's rotation.

You can only measure such slight effects with the most accurate clocks now available, made of a sapphire ring that is made to 'ring' with an incredible pure 'note', running accurately to better than one part in 100 trillionths of a second, albeit only for 300 seconds, then it goes unstable. Made by an Australian, I believe, coincidentally called Blair, so good luck in finding stuff on him in google... :)

The living are the dead on holiday.  -- Maurice de Maeterlinck (1862-1949)
 

Offline DoctorBeaver

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Re: time dilation
« Reply #14 on: 06/06/2005 13:22:39 »
Sorry, I meant a kettle of how water weighs MORE.
The kettle thing is to balance E=MC2. Hot water has more energy so M must increase to keep the equation balanced
 

Offline merarischroeder

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Re: time dilation
« Reply #15 on: 10/04/2012 01:53:29 »
Quote
The kettle thing is to balance E=MC2. Hot water has more energy so M must increase to keep the equation balanced

I have serious objections to such assertions! (But someone may prove me wrong)

When you heat the water, you are not adding mass! You are adding energy. If you are suggesting that when you add heat energy, you keep the heat energy but also gain mass, then you have discovered perpetual energy.

You can't assign E in an equation and convert to m, but still have 100% of E! And how does this conversion take place? What's the process?

The equation - E=mc2, doesn't mean that energy has mass, but rather energy can potentially be "converted" into mass. There's a fundamental difference!
 

Offline merarischroeder

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Re: time dilation
« Reply #16 on: 10/04/2012 02:40:05 »
Quote
But someone may prove me wrong

I think I can (being myself), having just finished reading the wikipedia article on E=mc2.

It appears that the formula does imply concurrent equivalence, that is, you may measure energy as energy or mass, because they are physically the same thing. One does not convert from mass to energy, they are concurrently the same.

Another example, is that a tennis ball travelling at the speed of light would be measured in the relative frame of reference as having infinite mass. Therefore it can be measured as having infinite mass as well as travelling at the speed of light (kinetic energy).

So there you go, if there's another ignorant person such as me out there that gets confused, hopefully they find this and don't have to waste as much time as I did to come to the answer.
 

Offline MikeS

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Re: time dilation
« Reply #17 on: 10/04/2012 08:18:39 »
It might just be worth pointing out that if you accelerated up to the speed of light time for you would ultimately stop.  You would not be aware of it as time would seem to be passing as normal in your own local reference frame right up to the point where it stopped.  At which point you wouldn't be aware of anything, as you wouldn't be aware of anything, as you...
« Last Edit: 10/04/2012 08:36:50 by MikeS »
 

Offline imatfaal

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Re: time dilation
« Reply #18 on: 10/04/2012 12:11:33 »
Ok - a hot kettle will have slightly more mass (as long as no steam has escaped) 

And Mike - please not on the main board.  There is no real consistent or reliable model for massive objects travelling at light speed (psst cos they don't!)
 

Offline MikeS

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Re: time dilation
« Reply #19 on: 10/04/2012 15:54:28 »
imatfaal

We all know they don't.  I only mentioned it because some people are under the mistaken impression that time dilation approaching c is not a real effect.
 

Offline yor_on

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Re: time dilation
« Reply #20 on: 10/04/2012 18:14:37 »
No, times arrow will locally tick the same for you always. No matter how close you get to lights speed in a vacuum. You can't get to light speed being made of matter so what happens there is a moot thing for us mortals :)

But you can get infinitely close theoretically, and doing so you will find your wristwatch to be the same relative your heartbeats, as when back on Earth.  You will also find yourself growing old in the usual manner, to finally die.
 

Offline MikeS

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Re: time dilation
« Reply #21 on: 12/04/2012 06:22:32 »
yor_on
What you say is true but it seems to me to me to rather miss the other side of the coin.

If you are in a spaceship travelling at 0.9999999999999999999 c for you traveling for 1 year in your time you would have traveled for an effectively infinite time in elapsed time.

At what point and in who's reference frame can you finally be considered to be dead?
 

Offline MikeS

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If you had a cat in a box in a spaceship travelling at 0.9999999999999999999 c is it alive or dead? ;-)
 

Offline imatfaal

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If you had a cat in a box in a spaceship travelling at 0.9999999999999999999 c is it alive or dead? ;-)

Quote
In fact, the mere act of opening the box will determine the state of the cat, although in this case there were three determinate states the cat could be in: these being Alive, Dead, and Bloody Furious.

    -- Schrodinger's Moggy explained (Terry Pratchett, Lords and Ladies)
 

Offline yor_on

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Ahh Imatfaal, it seems as we have the same exquisite taste in good literature :)
My next cooperation will be named 'Towel inc'
 

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