Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Rincewind on 01/10/2005 15:23:15
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I think the generally accepted interpretation of relativity says that when you go faster your time slows down. So, for example, the astronauts who went to the moon and back are slightly younger than other peeps who were born at the same time but stayed on Earth.
I was thinking, if a ship and some light left a planet then the ship came back, having aged less than the people on the planet, wouldn't the distance the light had travelled have to be different as well? Either that or it would have to have travelled at a different velocity for those on the planet and those on the ship, right?
Am I making some kind of basic error here?
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Hi andrew and welcome to the forum (good choice)[:)]
I was going to anwser your question but i tend to make basic errors also, so instead of trying.
If you wait a little while one of the many clever people on this forum will get back to you.
Or If you google time dialation and Relativistic Length Contraction you should also get an explanation. [:)]
A couple of links given basic explanations
http://en.wikipedia.org/wiki/Length_contraction
http://www.glenbrook.k12.il.us/gbssci/phys/mmedia/specrel/lc.html
http://www.glenbrook.k12.il.us/gbssci/phys/Class/relativity/U7l4e.html
Michael (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Frofl.gif&hash=481319b762ee9d57cda15e90d2e83ee6)
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Hello Micheal, nice to meet you:)
I like your comment about 'clever people':D
About length dilation...
...if the spaceship and the people who stayed end up on the planet at the same time and they could agree on how far away the light was, but not on how much time had passed, surely that means they wouldn't agree on a velocity?
Or does the light travel a different distance across space for each PoV but somehow end up in the same place?
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Rince/Andrew,
welcome to the best science forum on the net.
I'm not sure I understand your question.
Correction - I AM sure - I DON'T understand your question.
Could you give a more precise example? (e.g. who leaves what location when, where do they go, when do they return, where does the light beam go, etc.)
If you can make the example more specific, maybe I can give you an answer.
(And after that, maybe someone else can come along and give you a CORRECT answer.) [:)]
1.618033989 - everyone's favourite number!
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Okay, just answer this first and I'll decide if the rest of my question is worth answering:
Did the astronauts who went to the moon age less during their voyage than people who stayed behind on Earth, even if by a tiny amount.
(According to the theory of relativity)
Cos if they did... well, we'll get to that if they did.
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Cheers mate Thats any easy one,I'm good at the easy one's.[;)]
Yes they did age less in respect to the people they left behind on earth, but it was probably no more than seconds as the speed that their ship was travelling wasn't very fast in relativity terms.
Time is only RELATIVE to the observer.(RELATIVITY)
Different observers can observe time differently to each other.
If you were on earth and you could magically with no time delay see a clock in a fast moving spaceship, the faster the better,you would see their clock running slower than yours on earth[:)]
RELATIVITY CALCULATER LINK BELOW
http://www32.brinkster.com/snefru/space/srcalc/srcalc.htm
Michael (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Frofl.gif&hash=481319b762ee9d57cda15e90d2e83ee6)
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Yeah, ukmicky's right.
So ... what about the rest of your question, rincewind?
Solvay.
1.618033989 - everyone's favourite number!
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So if a beam of light left earth at the same time as them, and they went to the moon and back, they would then be able to agree with the folks who had stayed on earth about how far away the light was right?
The light is a certain distance, at this point, from the planet Earth, yeah?
So if they can agree on how far away the light is, but not how much time has passed, how can they agree on a speed of light (which is always constant. That's like a fundamental thingummy of relativity)?
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I mean, if they were going away from me, then I can understand their clocks going slower, but if they were coming towards me wouldn't their clocks go faster and catch up again? Logically speaking.
I know the equations call for the squares of velocities to be used which makes it (apparently) a scalar quantity and therefore independant of direction. But I'm not sure the maths hooks up with common sense on this one.
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Explanations are now getting harder. Let’s see how well I do
Their are two frames of reference here the first one is yours and the earths which as far a you and the earth is concerned remains constant,(no time dilation) and the second one is the spaceship that is speeding through space, and is now experiencing time dilation.
Time dilation slows down time for the observer experiencing it compared to there original frame of reference, which in this case is Earth
Your frame of reference won't change, its there frame of reference on the ship that is changing, they are the ones that have left you and the earth frame of reference and therefore it is them that is experiencing the effects of relativity.
For their time on the space ship to catch up with your time on earth,you and the earth would have to experience time dilation which you can't because the earths speed of travel through space remains constant.
Hmmm. It’s a bit long winded. Where’s my mistake, there’s got to be one coz it’s me.[:)]
have I gone wrong anywhere. or missed anything.
ps i quite enjoy trying to learn all this stuff. So be kind[:D]
Michael (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Frofl.gif&hash=481319b762ee9d57cda15e90d2e83ee6)
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Andrew - I understand your question now, and it's a good one. In fact, it's quite tough.
Michael's answer is absolutely right (as far as I can tell - although I'm no expert), but I'm not sure it really addresses the specific point in your question (i.e. just how far will the light ray have travelled, according to the each observer's calculations).
Will have to think about this one.
1.618033989 - everyone's favourite number!
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For them to get correct anwsers they have to make there calculations differently
The people on earth would make their calculation as normal.
The people who have returned from space would have to make their calculation taking into account the effects of relativity.
Both sets of people should then agree on everything.[:)]
Or am i still not understanding the question right.
Michael (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Frofl.gif&hash=481319b762ee9d57cda15e90d2e83ee6)
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Michael - you're absolutely right (again). But the question is HOW do they make their calculations?
Andrew(Rince)'s question, as I understand it, can maybe be represented as follows:
At noon, an earthling shoots off a photon of light into space, and simultaneously an astronaut shoots off to the moon.
At 10pm (earth time), the astronaut returns. But the astronaut's watch reads 9pm (say), due to relativistic time dilation.
Now, the earthling and astronaut are together again and share the same inertial frame of reference again. So they'll both agree about how far away the photon of light is - it's 10 billion km away (roughly - the speed of light is a bit over 1 billion kph).
So the problem is: the earthling says the photon has travelled 10 billion km in 10 hours, but the astronaut says it's travelled 10 billion km in NINE hours. So the astronaut thinks the light has travelled at a faster rate!
This problem has been driving me quite mad for several hours. But I think I might have a resolution now:
From the astronaut's point of view, the photon has NOT travelled in a straight line. The distortion of the astronaut's spacetime (due to her acceleration) means that, in the astronaut's 9 hours, the photon has only had to travel 9 billion km through the astronaut's spacetime.
Does this make sense to anyone? Can anyone tell me if that's (sort of) right or not?
And can anyone explain HOW to calculate the distance the photon travels through the astronaut's spacetime (in simple terms - i.e. without having to take a full course in general relativity)?
I sort of understand the maths of special relativity (where velocity is uniform), but I can't work out how to take into account the acceleration (i.e. the astronaut stopping and turning around at the moon).
Ta.
Solvay.
1.618033989 - everyone's favourite number!
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Hey Paul I seem to be getting good at this, maybe we should collaborate and come up with the new theory of everything.
You can be my research assistant.[:D][:D]
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As for your question maybe your trying to complicate things to much, your need to simplify things and take the journey as a whole rather than in stages.
Michael (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Frofl.gif&hash=481319b762ee9d57cda15e90d2e83ee6)
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Depends ... how much are you willing to pay for me to be your research assistant?
I need to read up more on relativity though - I suspect I still don't really understand it.
1.618033989 - everyone's favourite number!
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Now I’ve thought about the question a bit more, I think you’re right Michael – I’m overcomplicating things. Maybe it can be simplified this way:
While the astronaut is travelling, she sees the length (dimension in the direction of travel) of the earthling’s frame of reference contracted by a factor of 0.9 (i.e. same as the time dilation factor).
So while the earthling sees the photon travelling 10 billion km, the astronaut sees it travelling (inside the earthling’s reference frame) a distance of only 9 billion km. So she calculates the correct speed of light (9 billion km in the earthling’s frame divided by 9 hours in the earthling’s frame).
When the astronaut comes to rest (i.e. is no longer moving from the earthling’s point of view), she’ll agree with the earthling that the photon is 10 billion km away. She’ll just have a different perspective on how it got there!
(They must agree that the photon is 10 billion km away when they’re both at rest: if the photon hits a mirror at that point, and the astronaut and earthling stay still while they wait for the photon to return, they’d both see it arrive back at the same time, 10 hours later).
But I’m still not sure I’ve really “got” it – it smells funny to me. Can anyone tell me if the above reasoning is right or not?
"The early bird may get the worm, but it's the second mouse who gets the cheese."
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Mm, yeah, I suspected length dilation would be relativity's explanation, here's what I have to say about that:
There are a certain (well, random actually but with the law of averages and that...) number of quantum fluctuations in a given area of space. If you perceive that area to be squidged (as with the moving astronaut) you would perceive a higher density of quantum fluctuations, no?
If you were moving, the rest of the universe would have a higher KE relative to you so this could account for the higher number of quantum fluctuations except that a vacuum has no mass with which to 'hold' kinetic energy, but then neither does light, and that has kinetic energy so... bleuuurgh, I dunno.
But, I've thought about this alot, and I am as sure as I can be that relativity should be symmetrical. Your time should balance out and when you return to the same point in space, your time should be the same as those who remained there. I cannot understand how a theory of relativity can produce this objectivity. That is, that something which is 'moving' (in inverted commas because it all depends on the inertial frame) will lose time. That suggests to me that if you reversed the inertial frame (centred it on the 'moving' object rather than the 'stationary' one), it would be the 'stationary' object that lost time.
It's been suggested to me that acceleration is the key, but if that's the case why don't the equations take any notice of acceleration (I'm sure there are more advanced equations I haven't encountered yet that do apply to accelerating objects but the point is you can work out time/length dilation just from knowing the relative velocity of two objects, which one accelerated is irrelevant).
My answer is that velocity is unimportant, what matters is displacement. For every 300,000km you travel away from an object you lose a second, for every light-second you travel towards an object, you gain a second. How does that sound to everyone? (Don't worry about upsetting me if I'm wrong, as long as you explain why I'm wrong simply enough for me to understand, it'll stop me thinking about it and the whole reason I'm here is so that I can stop thinking about this and move onto something new to wonder about). Perception is reality in this case.
We could argue that when we see light from a distant star, it's a thousand years old, or whatever, but I would argue that as the light has been moving at the speed of light and therefore experiencing no time, saying it's old and far away is saying the same thing twice, and not truly understanding the nature of time as a dimension which passes through every point in 3D space. It would be more correct, in my understanding, to say the star is a thousand light years away, but what we're seeing is what is happening, not what was happening a thousand years ago. And if we could travel there in an instant we would journey a thousand years into the star's future, but looking back at our planet we would see it a thousand years before we left.
And this is real. And this is true.
Looking at space, the distance you are from something can always be worked out. If two of it's coordinates are 0,0 and the third is, say, 5, then no matter how you twist these dimensions your distance can always be worked out to be 5. I think the same is true when you account for the fourth dimension, and your distance can be measured either in kilometres (each=1/300,000sec) or seconds (each=300,000km) and these two units are interchangeable.
Someone should have sorted me out on this a long time ago, but the few I've managed to discuss it with (I'm sure you're all familiar with trying to discuss relativity with non-physicists) haven't shown sufficient understanding to convince me. One of them holds a 2:1 in physics but was satisfied once he could do the maths and didn't really seem to associate the maths with reality, but the fault's probably mine.
Appreciate the time you've spent already btw, Solvay:)
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In relativity, if you travelled a vast distance across space at close to the speed of light you would be a long way from where you started, okay, simple enough. If someone wanted to come after you, they could, and they would see you again, but if you were to travel back to them, they would have died hundreds of years ago. What kind of sense does that make?
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Originally posted by Rincewind
My answer is that velocity is unimportant, what matters is displacement. For every 300,000km you travel away from an object you lose a second, for every light-second you travel towards an object, you gain a second.
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Hi rincewind
As you know Im not and expert and will never be[:(],but what happens when an object travels around an object instead of away from it like the GPS satellites, which are now younger than they would be if they remained on earth?
Because these satellites are in constant motion around the earth the effects of relativity must be accounted for to maintain their positional accuracy. The newer satellite’s have three atomic clocks with an accuracy of 1 SECOND in a million years and have to continually communicate and adjust their times with earth base clocks because the satellites are in constant motion and due to relativity are running slower than atomic clocks on earth.
From what your saying if you turned the satellites around and sent them the opposite direction around the earth they would then make up any time lost when they were moving the other way and would be running faster than they were.[:)][:)]
Michael (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Frofl.gif&hash=481319b762ee9d57cda15e90d2e83ee6)
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Oh, is that really true? Damn.
Someone (a physics student) once told me that time dilation had never been proved, that for every experiment which had backed up relatavistic time dilation there had been several which had had the opposite result. That's what got me thinking along these lines.
My last two posts were a bit dodgy cos I was very sleep deprived but it's been something that's been playing around in the back of my mind for a while. I feel like it's been resolved now and I can get on with not worrying about relativity - there are far cleverer people than me who can do that:)
I still don't really understand why one thing (the satellite) counts as moving, and its time goes slower, while the other thing (the Earth) counts as stationary though. I guess the satellite is accelerating faster in gravity because of its lower mass but, as I said before, acceleration is not taken into account in the time/length dilation equations.
On top of that, relativistically speaking, a body doesn't accelerate in gravity, does it? It just travels in a straight line through warped space time.
Is that it? Is it because the satellite is travelling further through space time, getting to the same place. It's not accelerating, it's just travelling faster and further in a straight(ish) line, and that's why its time runs slower.
OK, if relativity is right, why can't they just program the correct time dilation into the atomic clocks so that they run at the right speed with respect to Terran clocks, why do they have to keep in communication?
I can't really get my head around circular motion very well. I guess an inertial frame can't be rotating because things obviously change when you're spinning, but what are you spinning relative to if there's no ether? How does the body or the particle or whatever know that it's spinning? Is it relative to the gravitational gradient maybe? These are questions that didn't really bother me when I was doing physics at school but I've wondered about it a lot since. I mean, a fundamental misunderstanding of what rotation is measured relative to or how rotation is measured could account for dark matter or dark energy or both, ay? It could, I'm not saying it will.
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Space travel accelerates the ageing process and is well documented, the body undergoes a massive acceleration of the age related illnesses we will all become familiar with.
So, the space travel actually aged their bodies faster than if they had stayed on Earth.
Secondly, the 1969 alledged lunar landing had the computer capabilities of a modern day pocket calculator. Given the difficulties NASA has in saending astronauts into space, let alone landing them on the moon, I have to admit to being very suspicious about the USA Government telling a few porky's. Furthermore, the footage of the early moon landing is highly suspect now that technology to evaluate it properly has moved on.
So In all probability and relativity to your question, the hypothesis of relativity is relatively wrong in this case at least.
"The explanation requiring the fewest assumptions is most likely to be correct."
K.I.S. "Keep it simple!"
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Did the americans land on the moon? well the russians believed it.and i believe it. oh and all the evidence as far as i'm concerned has proved it. so yes we did land on the moon.
And when we send men to mars,the sceptics will be out again saying the same things.
I believe this topic has also been discussed on this forum before.
Michael (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Frofl.gif&hash=481319b762ee9d57cda15e90d2e83ee6)
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Alrighty then, on your belief the Americans landed on the moon so they did. Wouldnt stand up in a courtroom Michael.
I have also seen the evidence and agree with the points raised about land marks in different places in relation to the angle of the photographs, the direction of shadows, the speed at which the doust moves when impacted by the astronauts feet, etc etc.
"The explanation requiring the fewest assumptions is most likely to be correct."
K.I.S. "Keep it simple!"
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hey you know that quantum laws dont have to obide by classical laws.
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Apologies in advance, but this may be a long posting - so I'll split it up into sections.
Firstly, Andrew K Fletcher:
Is there any chance you could post your conspiracy theory under another topic? Maybe create a new topic or resurrect an old topic where this has been discussed before (as Michael has pointed out)?
I don't mean to sound rude - I'm interested (though sceptical) re: what you have to say on the conspiracy theory, and I'm sure there are others who would be interested in debating it - it's just that the current topic is relativity, and going off on such an unrelated tangent will make the topic very confusing and impossible to follow.
Thanks.
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Secondly, Rincewind:
Some interesting challenges to relativity theory. Keep them coming, they’re getting me to really use my brain (for a change).
Re: the idea that displacement, not motion, causes time dilation – I think Michael’s example of circular motion dealt with that. (Nice one Michael – I wish I’d thought of that myself.)
Re: acceleration can’t be the key – hopefully you’ll find the following link as useful and interesting as I did. (The logic in this web page looks right to me, but I may be missing something.)
http://www.incentre.net/tcantine/TP.html
Re: symmetry in relativity – there IS symmetry in relativity.
You need to get past the notion of ABSOLUTE time and ABSOLUTE space (which relativity says don’t exist), and accept that all we can do is measure the DIFFERENCE in lengths between points, and the DIFFERENCE in times between events.
Relativity is symmetrical in that it says that two observers stationary relative to each other (and ignoring the gravitational field too, to be pedantic) will measure the same rate of ticking of a clock as each other. Their clocks may have different starting times (9pm and 10pm), but so long as they’re stationary, their clocks will advance at the same rate.
I’ve a feeling (but I can’t prove it … until I’ve studied relativity more) that the symmetry in relativity would be destroyed if time slowed down when an astronaut is moving away from you and sped up when travelling towards you – such that their clocks read the same time again when they rejoin each other. ((Maybe an example of circular motion would help here too, Michael??))
Symmetry in physical laws can be expressed mathematically by saying that some quantity or other is conserved – i.e. that the quantity is “invariant” (doesn’t change).
You’re right that in normal (“Euclidean”) space - in the absence of motion or gravity - the distance from the origin is “invariant” under rotation. Mathematically, this is expressed as the invariance of the “Interval” I, where:
I^2 = x^2 + y^2 + z^2.
(That’s just Pythagoras’ rule for a hypoteneuse in 3 dimensions, by the way.)
In relativity, the invariant “Interval” I is calculated as:
I^2 = x^2 + y^2 + z^2 – (c.t)^2
(No, don’t ask me how they derive that.)
The fourth term above, the (c.t) term, is basically agreeing with what you said earlier - that a time difference of 1 second can be treated as equivalent to a length/displacement difference of 300,000 km along a space dimension. But this (c.t) term is NEGATIVE in the above equation, not positive – which (I think, maybe?) sort of explains the counter-intuitive nature of relativity. (For example, it means that a rotation of the axes - due to motion – leads to time differences dilating and lengths contracting, rather than length and time keeping their normal relations to each other.)
Maybe I’m not actually helping here (someone who doesn’t really understand what he’s talking about quoting mathematical formulae at you) – but you started it with your (0,0,5) coordinates! [:p]
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Finally, can I suggest a couple of good (and cheap) books if you really want to get your head around relativity.
“Six Not-So-Easy Pieces” by Richard Feynman is a collection of 6 lectures (from the Feynman Lectures in Physics Vols I and II) that give an excellent grounding in relativity (and symmetry). It uses some “high school” maths, but I imagine it’s still useful even if you skip a lot of the maths.
(I’ve recently finished reading it. Obviously, I plan to read it a second time, in the hope that I'll actually understand it better on a second reading!)
And I've just started reading "Understanding Einstein's Theories of Relativity" by Stan Gibilisco - it looks very good too (simple explanations and lots of diagrams).
Right, I've written enough now to send everyone to sleep, so it's time for me to shut up again.
"The early bird may get the worm, but it's the second mouse who gets the cheese."
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To the question : Is relativity wrong ? Probably the answer should be that relativity is wrong for macroscopic objects. No macroscopic objects have ever been observed to travel anywhere near the speed of light , so none of the things to do with relativity need apply. The earth itself is revolving around the sun at about 28,000 m/sec. which is about 0.00009% of the speed of light , at these speeds the effects of relativity are negligible. Relativity does apply to sub-atomic particles and a lot of evidence has been found in support of it . For instance electrons accelearted to near the speed of light show an increase in mass of 11,800 times the electron at rest. And sub-atomic particles formed as a result of cosmic radiation striking the earth's atmosphere have been found to have life times 6 times as long as those made in the laboratory because they were travelling through the atmosphere at near the speed of light. Relativity is more to do with objects travelling at relativistic velocities , than with ordinary objects travelling at ordinary velocities.
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McQueen,
just because the effects of relativity are hard to measure (because they're so small) for macroscopic objects doesn't mean that relativity is "wrong" for macroscopic objects and only applies to sub-atomic particles!
Also, don't forget general relativity (GR). Special relativity (SR) only covers uniform velocities, but Einstein extended it to accelerated motion and gravity via GR. And the effects of GR have been experimentally verified (e.g. bending of light rays passing near the sun, oddities in the orbit of Mercury).
But then, while SR does apply to sub-atomic particles, they can't find a way of making GR work with such quantum particles (the elusive "theory of everything" / "quantum gravity").
"The early bird may get the worm, but it's the second mouse who gets the cheese."
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Paul ( Solvay 1927)
It was not my intention to say that time dilation only worked at the sub-atomic level , what I did want to say was that the effects are so small , that they are almost neglible in any real terms for instance in the example given in the starting post of the thread, time dilation for the astronauts might mean an increase in life time of about 0.0000001 secs , ( see : http://www.btinternet.com/~j.doyle/SR/sr4/sr4.htm ). On the other hand these figures are still understandable , if we take the matter wave associated with a car weighing 1 ton and moving at 10 km/hr we get a length of 10 ^-38m(approx.) which is totally unacceptable.
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Why is that unacceptable? When you say matter wave, does that mean the electromagnetic wave associated with the car's kinetic energy?
Excuse my ignorance:)
Solvay, so basically it's like adding the time coordinate to the space ones if time were an imaginary dimension and space's dimensions were real (as in imaginary/real numbers). Funky. Hm, I think that's what I thought. I mean I hadn't expressed it mathematically, or realised that it meant that time was imaginary but that when something was further away from you it was behind you in time, in a manner of speaking, and that if it moved toward you it would move forward in time to meet you.
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Andrew (Rince)
Matter waves , ( I feel ) are unacceptable because in terms of reality they represent infinities. It is unrealistic to talk of waves 10^ -38m long. ( and this for an object only weighing 1000 Kg and traveling at 10Km/hr ) Now if you look at Einstein’s equations they are always within reason. Even an object moving at a few millimeters a second would come within realistic ( excuse the pun ) limits.
Your second comment dealing with time co-ordinates , is interesting. (This applies to Solvay too. ) Personally ( and this is not saying much ) I do not believe in General Relativity. For me the space time continuum , represents a state where the speed of light can be exceeded. Imagine the scene in a fairly restricted space such as earth , dimensions no longer exist , because you can be in any place you want faster than you think, It would make no difference if you are in Rome or London because you could get there faster than thought , in fact you could be in both places at once ! Time would no longer exist. In such a situation you could be taking off from Heathrow to the States , and arriving there ( at Heathrow ) in another plane , just as your plane is taking off . So theoretically you could be in two , three or four places at the same time. What is amazing is that QM supports this view in its “Many World’s Theory. In truth reality is not like that. Everything observable in the Universe is governed by the limitations imposed by the speed of light. So , although space and time may in fact be , in some as yet not understood manner , related , it certainly would not have anything to do with gravity , which I believe , is a function of the ether.
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Rinceandrew - re: your comments on time being (at least mathematically) like an imaginary dimension - as in SQRT(-1) - that sounds sort of right to me.
"The early bird may get the worm, but it's the second mouse who gets the cheese."
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But, doesn't it work out that the mass of a body tends to infinity as it's velocity tends to the speed of light? Or is that a false assumption that I've picked up from somewhere? (I've done a lot of learning by talking so I'm never quite sure of my facts)
I think we could reach the speed of light if we somehow, rather than adding extra kinetic energy, we converted our rest mass into pure kintic energy or em radiation or whatever you want to call it, then managed to re-focus it, re-congeal it, turn it back into rest mass basically (a la Star Trek). But I don't think we can go faster than it. But I'm open to argument, no TOEs or GUTs have shown up yet:)
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quote:
But, doesn't it work out that the mass of a body tends to infinity as it's velocity tends to the speed of light? Or is that a false assumption that I've picked up from somewhere? (I've done a lot of learning by talking so I'm never quite sure of my facts)
Correct the relativistic mass of the object will become infinite if it approaches the speed of light.
Michael HAPPY NEW YEAR (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Fparty-smiley-012.gif&hash=844994fd61764508c533537d6874634d)
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Hey Mickey, you're still here:)
and Solvay, I followed that link about time dilation (you've probably forgotten about it by now but if you do remember...). At first I thought it wasn't relevant because the example isn't a return trip, it's one way. Then I thought it might kinda make sense. Then I thought it wasn't really relevant because a fraction of a second later the rest of the train or whatever would catch up and, I suppose the average amount of time your body, or your brain, or whatever parts of your brain perceive time, or your watch, or your radiation meter, has experienced as to how much time has passed. And my point was that if you got back to the same place, you'd be back in the same time as the people who hadn't moved. Otherwise what's that coordinates thing all about? I don't think that link really addresses that, but it took some brain bending to get me head around it so I'm not sure I've got it right.
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Cant remenber mate but i do remember you[:)]
Michael HAPPY NEW YEAR (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Fparty-smiley-012.gif&hash=844994fd61764508c533537d6874634d)
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I have just caught up with this long thread and think that those anti relatavists have forgotten one important detail. The original reason that Einstein started on the theory and its rather non intuitive results, was that the most fundamental laws of the universe are: energy and angular momentum are conserved (ie you don't get something for nothing) and the laws of physics are much the same wherever you are. The rest follows.
As has been clearly demonstrated the fine dtails have been and are contiually being confirmed on a daliy basis.
OK there may well be some deviations in very extreme conditions and these are continually being questioned and investigated but they are certainly no problems with relativitiy as a small correction to classical Newtonian gravity anywhere we are likely to go.
Learn, create, test and tell
evolution rules in all things
God says so!
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quote:
Originally posted by Rincewind
Hey Mickey, you're still here:)
and Solvay, I followed that link about time dilation (you've probably forgotten about it by now but if you do remember...). At first I thought it wasn't relevant because the example isn't a return trip, it's one way. Then I thought it might kinda make sense. Then I thought it wasn't really relevant because a fraction of a second later the rest of the train or whatever would catch up and, I suppose the average amount of time your body, or your brain, or whatever parts of your brain perceive time, or your watch, or your radiation meter, has experienced as to how much time has passed. And my point was that if you got back to the same place, you'd be back in the same time as the people who hadn't moved. Otherwise what's that coordinates thing all about? I don't think that link really addresses that, but it took some brain bending to get me head around it so I'm not sure I've got it right.
Hi Andrew, welcome back, long time no see.
But I'm afraid I'm clueless about the time dilation link you refer to. (Can you remind us?)
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Oh, sorry, I just looked back on page 1 of this thread and realised what you were referring to.
All I can say is ... I'm still confused by all this relativity business! [:D]
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quote:
Oh, sorry, I just looked back on page 1 of this thread and realised what you were referring to.
Me too[:I]
Michael HAPPY NEW YEAR (https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fi11.photobucket.com%2Falbums%2Fa186%2Fukmicky%2Fparty-smiley-012.gif&hash=844994fd61764508c533537d6874634d)
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Hi there
Just went through the discussion quickly, so I may have missed something.
One main problem I see with the reasoning is the attempt to apply special relativity to a problem that includes non-inertial systems of reference.
The twins paradox is only brought up in text books to demonstrate the weirdness of relativity, when compared to newtonian mechanics. However, it can't bedescribed fully in the scope of general relativity. The key point is that the astronaut twin leaves the earth - ie, accelerates to a speed, travels for so long, then comes back, etc. This is not an inertial reference system.
If you don't take into acount accelerations, you end up with a very symmetrical situation. The astronaut twin travels at a certain speed with respect to the earth twin. But, the same goes for the earth twin (ok, take him of the earth, and put him on a space station). He also travels with the same certain speed (opposite direction) with respect to the astronaut.
The difference between the two is that the twin who leaves earth accelerates to a certain speed, etc. as I said earlier.
Don't ask me to describe what's up in the twins paradox in term of general relativity!!
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Hi there
Just went through the discussion quickly, so I may have missed something.
One main problem I see with the reasoning is the attempt to apply special relativity to a problem that includes non-inertial systems of reference.
The twins paradox is only brought up in text books to demonstrate the weirdness of relativity, when compared to newtonian mechanics. However, it can't bedescribed fully in the scope of general relativity. The key point is that the astronaut twin leaves the earth - ie, accelerates to a speed, travels for so long, then comes back, etc. This is not an inertial reference system.
If you don't take into acount accelerations, you end up with a very symmetrical situation. The astronaut twin travels at a certain speed with respect to the earth twin. But, the same goes for the earth twin (ok, take him of the earth, and put him on a space station). He also travels with the same certain speed (opposite direction) with respect to the astronaut.
The difference between the two is that the twin who leaves earth accelerates to a certain speed, etc. as I said earlier.
Don't ask me to describe what's up in the twins paradox in term of general relativity!!
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Can anyone tell me what branch of physics or what version of relativity the interval equation comes from? The one Solvay said: I = x2 + y2 + z2 - t2 (we should have superscript on a science forum really)
Cos if I is invariable then that basically says what I was saying at the start, and it excludes the twins paradox (as I understand it).
I don't really know the differences between special and general. I thought special was wrong because Einstein had invented a constant to make the results fit the static universe model. If this is true what's the point of special since general came along?
(guessing from madmortigans post - general takes into account acceleration while special just talks about relative velocities, but please expand and/or correct that guess)
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General relativity describes accelerating reference frames. Its math is hard. Special relativity is much easier and can be done with college level math. Thus I strongly suggest getting a textbook and solving all the problems - shouldn't take long. Popular science - although quite fascinating, doesn't give enough hard facts for anyone who feels curious about stuff.
Tha famous constant for anti-gravity was invented by Einstein in the scope of general relativity, right before Hubble poseted his findings on galaxies moving away from each other, thus suggesting an expanding universe.
I'll go back to check that equation, but I've got to go now, need to file my tax return (speaking of relativity and the lot!)
go with the force!
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Andrew,
the invariant spacetime interval I = x^2 + y^2 + z^2 - (ct)^2 comes from relativity - I think it's specifically from the attempts (by Minkowski?) to give a geometrical interpretation to relativity. And note that it applies to special as well as general relativity.
MadMort's right that the only difference between special and general is that the former (1905) only applied to inertial (uniform constant motion or rest) frames of reference, whereas the latter (1914/15) extended that to non-inertial (accelerating) ones. The special theory is just a "special case" of the general one - it's not wrong, it's just "incomplete".
The "cosmological constant" that you're getting confused about is a "fudge" that Einstein put into his general relativity formula to ensure that the universe was static. He later said that this was his "greatest blunder" because his theory (without including this "fudge" constant) predicted that the universe was expanding. So if he'd left the constant out and said "I predict the universe must be expanding", he'd be looking very smug when Hubble confirmed this prediction in the late 1920s.
Hope that helps.
Paul.
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Cheers geez, that's brilliant:)
You know, when there's something you should know and should have known a long time ago, but have only just found out? Like a fog lifting, nice one:)
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Dya see what the equatino means, yeah? If you reduce the three spatial dimensions to a resultant distance s, you get I = s^2 - ct^2... hang on, where'd that c come from? Musta missed that the first time round, What does that mean?
I'll get back to you
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the distance two events are from each other, minus the distance light has travelled in the time between these events, is invariant.
Hmm, must sleep, but thanx for clearing up the relativities for me.
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The peaple on the space ship would percive a diferance to the peaple on the earth but the ship wood be in red fase going awaiy and blue fase coming back so were is the time diferance.
sorry for the speeling, Half a bottle of op rum
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Andrew - I think that's a fair way of describing it, yes.
Allmee - you really were p*ssed, weren't you! (I can't say you've inspired me with the confidence to invest in your perpetual motion machine, though. [:)])
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So it's kind of like the pythagoras triangle, except it's kind of got two hypotenueses and only one regular side (or three regular sides and two hypoteneuses if you take the three spatial dimensions as three dimensions); that is the area of the square of one side (the distance) minus the area of the square of either of the other two sides (the distance light has travelled, and the interval) leaves the area of the square of the remaining side.
Interesting concept.