Did Anyone Get Confused By The Wording Of The Time Dilation Question (1 Viewer)

[Affinity]

Originally posted by Morgantic
Guys... the answer is 8.77777777.....
The spaceship has moved towards the speed of light, therefore undergone relativistic effects. So the time on earth is 16.77777777 when the ship arrives at this imaginary star, but because the star is 8 lightyears away from earth (0.8c x 10 years), the clock will only show 8.7777777 from the perspective of that spaceship at that star, because the light of the clock travels at the speed of light like all light

Whoever argues that it is the earth that moves is an idiot, as no energy is put into the earth to accelerate it to these speeds, otherwise the earth would gain a lot of mass by relativity for no specific reason and with no energy input to itself.

The BOS is crap, that question didn't give enough information to fully understand what was happening, neither did it give a correct answer.

paragraph 1:

sentence 1: everything undergoes relativistic effect.
sentence 2: you're confused with your distances. it's 8 lightyears for the spaceship but it's 80/6 = 13.3 light years for earth.
and
The derivations for those relationships in the lorentz transformations are slightly more complex than just thinking about the lag that light requires to travel.




paragraph 2:

general comments:

You should already know that mass is not absolute, the mass of something is lightest when observed from it's own frame. Earth will not gain mass from the earth's point of view even if it's the earth which moved and the earth will always be heavier than it's rest mass to the astronaut in the spaceship.

back to your point on acceleration, the question stated that the ship travelled at 0.8 c and the journey took 10 years as seen on the spaceship. acceleration and other weirdo general relativistic effects is not an issue here, time is measured after the spaceship is accelerated.

paragraph 3:

hmm no comment on that, perhaps I agree in secret

 

[Affinity]

I hope BOS could now see the problem of taking out too much maths from physics and replacing them by words

 

[NSBHSchoolie]

Might I just add the question doesn't mention acceleration at all? It says nothing about leaving earth at rest...you can safely assume he starts at 0.8c. Then when he gets to the star, there is no turning around, no stopping mentioned. Therefore...special relativity.

D.

 

[toknblackguy]

no...it's a thought experiment, and u don't think outside ofthe question, ie don't think about how he managed to get to 0.8c, or how the hell he is able to look at the earth's clock!

however, special relaitivty is all that holds, but this means that because he is in an inertial frame of reference, he could be moving at constant velocity or not at all!
therefore, when he looks at earth, he would see the earth disappearing at 0.8c. hence, this "moving" FOR has time going slower. HENCE B!!!

 

[Kent_Cadarn]

It all depends on what we consider the rest frame, since the questoin asks for it from the perspective of the astronaut and 10 years have past and this is the rest frame.
so t = 10 and tv = 16.7.
Time is dilated i.e. gets bigger, it doesn't contract like length. This is a straight forward question that only gets hard when you think "what if"

 

[walla]

I'm going to summarise, in very rigorous logic, the "B" argument, some "D" idiot tell me where you disagree...

1) We assume that we are ignoring acceleration

2) Therefore we approach the question with special relativity

3) Given that approach, both the spaceship and the Earth are inertial frames of reference. Neither is more special than the other - both are undergoing relative motion. You cannot say that the Earth is still and only the spaceship is moving. We will not argue on this point.

4) As we are approaching it from the spaceship's perspective, we assume the astronaut thinks (s)he is stationary and the Earth is moving at 0.8c relative to the spaceship.

5) According to relativity, a stationary observer seems time run slower in an inertial frame of reference moving relative to themselves.

6) Hence, the astronaut sees time run slower on Earth than their onboard clock.

7) So if they see 10 years pass onboard, and time on Earth runs more slowly, less time has passed on Earth. Hence the answer is less than 10 years. Sub it into the equation and you get B.

Where do you disagree? If it's (3) then don't even bother posting a reply...you can keep your wrong opinion to yourself. If you see a problem somewhere else please point it out.

 

[Belle]

I have a suggestion....

This whole argument is not going to get anywhere because no-one from either side is going to back down. Which is fair enough I suppose, each side has their arguments.

But why don't we just leave it until the marking guidelines come out, then we can see which side is wrong in the BOS opinion and THEN argue your hearts out.

But this is really quite pointless. And besides, can I remind everyone that this question is worth all of ONE MARK! Does it really matter enough to devote all this argument to??

 

[toknblackguy]

of course it does!
because as we all should know by now
B IS CORRECT!!!

 

[freaking_out]

look ppl, stop fighting over 1 mark!!! the markers when they release their answers, then we'll go and fight.

physics is over everyone- OVER!!!!- so just let it go.

btw, it was D!!! (J/K)

 

[Bannanafish]

Originally posted by Kent_Cadarn

Time is dilated i.e. gets bigger.

hahahahah i rest my case

 

[Morgantic]

Originally posted by Affinity
sentence 2: you're confused with your distances. it's 8 lightyears for the spaceship but it's 80/6 = 13.3 light years for earth.

Yeah, I realised that last night, which would mean that it would be 3.3 years on the clock, according to that set of logic at least

Originally posted by Affinity
You should already know that mass is not absolute, the mass of something is lightest when observed from it's own frame. Earth will not gain mass from the earth's point of view even if it's the earth which moved and the earth will always be heavier than it's rest mass to the astronaut in the spaceship.

I always assumed that if you were close to the speed of light, you would possess increased mass and that's why you can't get above 'c'.


Anyway:
Ship clock slow - the distance is 13.3 light years, that means that when the ship arrives, it will see the light that left earth 13.3 years before it left. If the clock on earth shows 16.7 when it arrives, then the ship will actually see 3.3 years.

Earth clock slow - the distance is 4.8 light years, so it takes light 4.8 years to get there. So 10-4.8 = 5.2 years into the journey on the ship's clock that the light left earth. Dialate that by the fact that the earth's clock is slower and you get 3.12 years.

Tell me where I'm wrong with those (I'm sure I am), but as far as I can tell none of the answers took into account that light isn't instantaneous.

 

[LadyMoon]

It kinda stupid because one must also take into account that if an astronaut is to look outside through the window (given that he has a very powerful telescope) the time it takes light from earth to acutally reach him.
think abt it we see supernoveas that happened hundreds of years ago, beacuse only now light has reached us. Same thing with observing universe in "prehistoric times", if we can see a distance of 18 billion lightyears then we can see how the universe actually began. ---this is actually true for those of you dont know. Scientists have been trying to see into the past, by looking into the distances.
So if you apply the same concept to this astronaut case: then it will take a further 8 years before light from eart can actually reach him and tell him the time on earth at the particular moment!!! So if he wants to know the time on Earth at the time he arrives on the other planet, then he must wait 8 years and look out the window!!

regardless the answer to this question, you must agree it makes you scratch your head alot!

but anyways the answer is D anyway...look at my explanation on pg7.

 

[LadyMoon]

Damn! Morgantic beat me to this!

 

[Morgantic]

Oh well, at least we're in agreement on the point that light moves at the speed of light instead of at some crazy, magical, instantaneous value that the BOS seems to believe.

Does anyone know someone who is a physics nerd for a living and could sort their way through this mess. I seriously don't believe its B, but then again I have no case against it because its still plausible.

CURSE HSC ENGLISH FOR MAKING ME READ ENDER'S GAME!!!!!!!

*cough*, well yes, that's why I believe its D, because of Ender's Game and a few physics videos I saw

 

[Affinity]

byt subtracting 13.3 by 16.7 you're using galilean transformations, and in the speed of light doesn't remain constant for this, violating assumptions for special relativity

 

[Constip8edSkunk]

lol i didnt do changing worlds, but i actually thought enders game was an alright book... but how does it have anything to do with physics? with the instantaneous communication over billions of lightyears and all....

 

[dieselboi]

I had B! I believe it is right because i reasoned it the same way several of you have. In inertial frames of reference the earth will appear to be moving away as observed from the spaceship. therefore the spaceship is stationary and earth has a speed of 0.8! i was very confused and was gonna put D, but i thought the BOS wouldn't put something that easy in there (me is a complex thinker!) so is solved it and i got B... Lets hope the B'S are right. who's with me???

 

[Morgantic]

Originally posted by Affinity
byt subtracting 13.3 by 16.7 you're using galilean transformations, and in the speed of light doesn't remain constant for this, violating assumptions for special relativity

So what is it? 8 years as I said previously and you flamed me for? Or is light instantaneous like the BOS assumes? Whatever it is, stop flaming my posts and be constructive by correcting them, since no-one else seems to know the truth.

I also don't see how I'm violating any assumptions of special relativity by calculating distance in light years and saying light would take that many years to travel that distance, isn't that the point of the measurement?

 

[Dave_B]

Originally posted by LadyMoon
Hang on!
According to this:
"If the observer sees something to take 10 seconds according to his watch, then he sees the clock inside the train go 6 second.
If the passenger sees something to take 10 seconds according to his clock, then he sees the watch on the observer to go 6 seconds."

So say the astronaut travells to a distant planet at the speed of 0.8c and it takes him 10 years (relative to him). According to your explanation he would look out the window, look at the clock on Earth and see it show only 6 years....ok?
Now the astronaut comes back to Earth, suppose he doesnt land yet he looks at the clock on Earth, and again according to your explaination, he should now see the clock on earth show 12yrs. And the onboard clock on the space craft 20yrs.

Here comes the good part!
Now the astronaut gets out of the spacecraft and lands on earth! So according to the twin paradox the Time on Earth is actually faster than the time on the spacecraft.
So you are actually saying that when the astronaut gets out of the spacecraft and looks at the clock on Earth he sees it as 33.33 years????

LOL
Your explanation is funny!

but he can't go back to earth, cos that would mean he would have to decelerate, and we all know that cos its a special relativity question there is no acceleration.



the astronaut will look at the clock on earth, and see time dilation, as in less time has occured.

AT THE SAME TIME

an observer on earth will look at the clock on the space ship, and see time having dilated.

Thats the paradox of it all.


the theory of General Relativity (which is NOT in the syllabus) solves the argument you are talking about

 

[Affinity]

"little knowledge is a dangerous thing"

-what have the physics syllabus done to us?