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Enter the Relativity Challenge
An anonymous reader writes "Any slashdotters wanna pick up a lazy 25,000 Euros? All you have to do is explain Einstein's theory of relativity in a five minute multimedia presentation. The Pirelli Group have laid down this 'Relativity Challenge' to anyone as part of the International Year of Physics. Entries close on 31 March 2005."
"A Man has got to know his limitations."
I found mine in Physics 21 when we hit Relativity. I just flat out don't get it. I can do the math, and get the right answers, but I couldn't truly explain it.
"As God is my witness, I thought turkeys could fly." A. Carlson
Einstein's work was already in very simple laymen's terms. I don't know what the point is in trying to make it into braindead powerpoint.
I've had enough abrasive sigs. Kittens are cute and fuzzy.
...just remember that PowerPoint is not "multimedia."
Yeah, right.
Explain females to the slashdot crowd in 4 minutes, and I'll give the winner a copy of Duke Nukem Forever
Special, General, or both?
Special's not so bad, but General gets tricky...
www.eFax.com are spammers
Don't forget that this is the "SPECIAL Relativity Theory" - not the "GENERAL" one...
I found is in Relativity and FTL(faster than ligth) FAQ http://www.physicsguy.com/ftl/
This explanation explain relativity in context with the faster than light travel. Needs elementary math and explains lucidly why the time dilation occurs. Highly recommened.
I spent hours trying to understand the twins paradox until it was explained to me that special relativity does not explain the twins paradox, only general relativity; and that the school book that went on about the twins paradox taught only special relativity.
Thats my excuse, its till on my list of things to learn.
Sam
blog.sam.liddicott.com
This could be done in ASCII. The lameness filter is costing me 25,000 Euros!!!
Direct away from face when opening.
When you are courting a nice girl an hour seems like a second. When you sit on a red-hot cinder a second seems like an hour. That's relativity. -Einstein
I don't think it can be said much better.
The best relativity resource I've found is an in-depth online book called "Reflections on Relativity". Be warned, it's the real deal; read it slowly and carefully. Intro calculus should suffice to get you through chapter one (which took me about two weeks spare time in the evening to read and digest), after that it gets tougher, although I'm finding the subjects don't build on each other so much after that so you can skip something you can't follow and keep going. (On the other hand, I only just finished Chapter 2, of 9.)
:-)
About the only thing I can tell you, short of linking the book as I did or quoting it more extensively than Slashdot will allow, is that nearly everything physics fanboys think they know is wrong. Don't rely on Star Trek for your physics, get the real deal; it'll only take as much time as a few episodes of Star Trek and you'll feel much better about your expanding horizons
Special Relativity is much easier to explain in layperson's terms.
You could've hired me.
Every book I have ever encountered re: Relativity (and I have about 6) spends about 3 lines on the '... and the speed of light is constant' part and about 180 pages on the almost trivial vector math to determine the relative motion of an object from two different frames of reference (which IMHO, is just a huge, long-winded setup of the fact that trivial vector math doesn't work). BUT the fact that the speed of light is constant is the thing that breaks the model and no one ever explains that! It's just referred to axiomatically. In the book I would like to find, the whole book would be about how and why the speed of light is constant and then in the appendix they could state 'And oh, by the way, the speed of light being constant means that time dilation occurs and Lorenz tranformations have to be used instead of trivial vector math in order to figure out the position of objects in space and time'. Anyone know that title of that book?
You can't just wave it off saying the one that experienced the accelleration will have their clock slow down. If you want to calculate how much less one person aged, you go by how long (time and distance) they were travelling at that speed. For example, if I accellerate to 0.999999c in about a year (I think that's about 1g accelleration) and travel 10 light-years and back, then 24 years will have passed on Earth (20 travel + 4 for accelleration), but I will have aged only about 4. If I undergo the same accelleration but travel 10,000 light-years and back, then 20,004 years will have passed on Earth, but I will still have aged only about 4. The accelleration didn't make time pass more slowly, it was the period while I was tavelling at high speed that made it pass more slowly. Take both examples together and the one would seem to have 4 years pass and the other would seem to have 19,984 years pass, even though they experienced the same accellerations.
This also leads to an absurd result from my point of view. I will have only seen 2 years go by, but I will have travelled 20,000 light-years. From my point of view I would have been travelling 10,000 times the speed of light. How can this be?
I think it has to do with contraction. Lorentz contraction is one thing I haven't understood, how you can measure the length of something that is going nearly the speed of light? Apparently, when you are going nearly the speed of light, everything else contracts in the direction of your travel. For instance, if you were going a certain speed and passed a meter stick, it would appear to be only 1 millimeter long, although a stationary observer by the meter stick would see it as 1 meter long.
Now as for how fast you are going, that is all relative as well. If I take off from earth and accellerate to 0.999999c for about a year and travel 10 light-years, I don't think I'm going 10 light years. Space and the galaxy will seem to contract along the direction of my motion. When I get 10 light-years in space, it will appear to me like I have travelled a much shorter distance.
Here's a more concrete example. Let's say that I pass Earth going at velocity V, which slows down time for me to 1/10th normal. Then I travel to a space buoy that you have measured from earth as 10 light years away. Not only will I reach that buoy in about a year, but I will think I have travelled much less than 1 light-year because space along my direction of motion has contracted. During that time, an earth-based observer thinks 10 years have passed. The reason that his clock doesn't appear to slow down for me is because I don't think he's travelling that fast. To me, he has travelled much less than 1 light-year because space contracted and I think it was in 1 year, so he is travelling much slower than the speed of light and subject only to minor relativistic effects.
Slide 1:
Explanation of the Theory of Relativity
Boarder
10-18-2004
*rocket clip art zooms across screen*
Slide 2:
The speed of light in a vacuum is
*flies in from left* CONSTANT
Slide 3:
*in really, really small font, appearing one per mouse click* all equations proving relativity
Slide 4:
Conclusion:
*line fade* Everything is relative
Slide 5:
Special Thanks to:
*flashing text* Einstein
and
*spinning 3d text* Maxwell
*tiny red text* copyright 2004 boarder
IANAL, but I play one on
From this explanation. Twin A stays on Earth and Twin B sets off in a spaceship going 0.995 c (time and space will dilate to 1/10th). He reaches a point C that is 9.995 light-years away and heads back at the same speed. Let's assume accelleration is instantaneous. When Twin B leaves earth, both twins agree their clocks read zero. When Twin B reaches point C, Twin A sees that his clock reads 10 years and Twin B's clock reads 1 year. Twin B thinks his clock reads 1 year and Twin A's clock reads 0.1 year. As soon as he turns around, Twin A still thinks B's clock reads 1 year and his clock reads 10 years, but Twin B thinks his clock reads 1 year and Twin A's clock reads 19.9 years. It all depends on your frame of reference, and the accelleration changes that.
Personally, I don't think I will ever understand it. I think it's all philosophical because it is dependant on definitinitions. What does "observe" mean. What is "simultaneous"? Until you start studying special relativity, these terms are pretty easy to understand. I think physicists should come up with new words to describe these relativistic concepts and not use "observe" and "simultaneous" anymore in physics discussions. I have a special relativity textbook and the book contradicts itself on the meaning of those words in the first few chapters.
I saw Brian Greene buying a copy of "Flash for dummies".
Putting syrup in coffee is some form of blasphemy.
The difference between general and special relativity: General relativity has acceleration. The twins paradox has a rocket ship turning around, which means its velocity changes, which means acceleration must occur. This makes it a general relativity problem.
But one thing physicists do well is neglect values which are insignificant. When doing the twins paradox problems, we make the reasonable (within the context of learning the stuff) presumption that the time to turn around is not significant. But this is, of course, within the world in which it is reasonable to make a spaceship going a significant portion of the speed of light.
I always took these paradoxes as a good way of illustrating that the math works if you're consistent, even if you can't visualize or get a more "core" understanding of it, because the math is the core of it. After all, you can't actually visualize the wave nature of matter. People /draw/ it like a particle running along a sinsoidal path, but that's not accurate. It's a visual aid whereas the underlying math is accurate.
The point of the competition, as I see it, would be to make it clear that (1) certain expectations seem reasonable (additive velocity), invariance of Maxwell's laws, (2) these things break down with traditional viewpoints (Maxwell's laws and Gallilean transformations), and (3) we resolve this problem through the application of math doing even stranger things (lose invariance of additive velocity, get Maxwell's laws back). It no longer seems reasonable to our everyday experiences, but it works mathematically.
You like splinters in your crotch? -Jon Caldara
In relativity, "simultaneous" means an event occurs at the same time in the same reference frame. Where a (inertial) reference frame is one that is not accelerating -- all objects in the frame are at the same velocity. If you add acceleration, you hit general relativity which is beyond my understanding at present.
For every reference frame, we have a set of coordinate axes (x_frame12345, y_frame12345, z_frame12345). An event can be described as a coordinate and a time in a given frame (x_frame12345, y_frame12345, z_frame12345, t_frame12345). Simultaneous is meaningful only when you're talking about the simultaneous events in one frame. So, say you're in frame12345 and two events occur in the frame (0, 0, 0, 0) and (0, 0, -5, 0), so they'd be simultaneous in that frame. But in frame12346, those events may be something like (0, 0, 0, 0) and (0, 3, -8, 10). So in that frame they would not be simultaenous. Therefore, any observer must be assigned to a frame for his observations to be useful.
Hope this helps.
You like splinters in your crotch? -Jon Caldara
...Insignificance (directed by Nicolas Roeg). Check it out.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
The way I see it, as you accelerate (or get closer to a gravity well, whatever...) The dimensions of time and distance swap. Lengths contract because your x direction is now pointing slightly into a stationary observers' time direction. Events which appear to be simultaneous to a stationary observer have a little x and t swapped around and are not seen as simultaneous to moving observer. You can see events ahead of you now that are in my future, and events behind you that are in my past. .8c) he is carrying a 20m pole in the direction of travel.
Allow me to demonstrate:
Lets say a moving observer A is travelling so that lengths are contracted 50% (about
observer B has 2 light gates 10m apart and see's A's pole as 10m. At some point A's pole will appear to be completely between the light gates.
But from A's perspective the gates are only 5m apart. The front of his pole will break the second gate before he passes the first gate, and he's be out the other side before the back of his pole clears the first gate.
At the point where A is in the middle of the two gates, the front of his pole is sticking into B's future (where it has already passed through the second gate), and the back of his pole is sticking onto B's past.
09F91102 no, 455FE104 nope, F190A1E8 uh-uh, 7A5F8A09 that's not it, C87294CE no. Ah! 452F6E403CDF10714E41DFAA257D313F.
1) Explain Relativity
2) Enter Competition
3) Profit (for real!!)
The grand prize, for the explanation of special relativity, can only be won by an Italian national born after Dec. 1983. Read it here: http://www.pirelliaward.com/ch2_eli.html
Il grande premio, per la spiegazione della relatività speciale, può essere vinto soltanto da un cittadino italiano sopportato dopo dicembre del 1983. Colto esso qui: http://www.pirelliaward.com/ch2_eli.html [ pirelliaward.com ]
They had a good example of that in the article. If someone in observer B's frame closed the light gates instantaneously with observer A's pole inside them. The gates closing would be simultaneous to observer B. Observer A however would see the front gate close and open just before the front of his pole went through, then would see the rear gate close after the rear of his pole was through it. The two events would not be simultaneous to observer B.
In relativity, "simultaneous" means an event occurs at the same time in the same reference frame.
Actually, no. In relativity, "simultaneous" doesn't mean anything. That's half the point.
Before relativity, we had several ways of describing causality - we could say that "event A happened before event B", "event A happened at the same time as event B", "event A happened after event B" - and those definitions seemed absolute, just like the distances between objects were absolute - the distance between point X and point Y was D.
But relativity changed that.
That's because the notion of the "temporal distance" between two objects (that is, "dt^2") isn't invariant between reference frames. Neither is the spatial distance (that is, "dr^2 = dx^2 + dy^2 + dz^2").
any observer must be assigned to a frame for his observations to be useful.
That's the part that's a little wrong - see, there are several invariants - things that are the same in all reference frames - in relativity. Specifically, the proper distance, or "ds^2 = (cdt)^2 - dx^2 - dy^2 - dz^2". In *every* reference frame, that quantity will be exactly the same. So you can speak of quantities without reference frames. I can say that the proper distance between the point and time at which a photon from a lightbulb was emitted to the point and time that my eye registered it is zero - and every observer would agree with me.
So while before we could say "before, simultaneous, after", we now can say "spacelike, lightlike, timelike" - if the proper distance is less than 0, equal to 0, or greater than 0. In *any* frame, those measurements will stay the same.
It's important to recognize that relativity doesn't say that *all* measurements are subjective. Of course it doesn't say that - the speed of light, for instance, is the same in all frames. What it does say is that a lot of the quantities we used to measure are subjective - specifically, spatial and temporal displacement, momentum, and even things like electric and magnetic fields. Those are relative - but there are quantities underlying them which are invariant.
Just thinking... When Twin B decellerates at point C, the distance between him and Twin A appears to grow from 0.9995 light-years to 9.995 light-years. How can this be? In essence, Twin A would move about 9 light-years away in whatever time it took Twin A to decellerate. I think 1g accelleration over about a year (352.5 days) would get someone to about 0.995 c. So at a realistic rate of decelleration, Twin A would appear to move more than 9 light-years in less than a year...
How stuff works in Einstein's theory of special relativity? is a good starting point for the contesters.
Slashdot = Sarcasm
The 2 important points.
g) PIRELLI RELATIVITY CHALLENGE: in order to commemorate the centenary of the publication of the special relativity theory by Albert Einstein in 1905, we are introducing a special prize for the best multimedia product that describes the special relativity theory to the layperson.
and
Participation in Article 2, section g) is open to all individuals and organizations.
It helps if you can read.
What idiot freakin moderator modded the parent overrated? Are you fucking stupid? How can it be overrated when it was never rated in the first place?
So maybe it wasn't all that funny, but that isn't the same as overrated... if it were modded Funny and you didn't agree, then maybe you can mod it down. Modding is supposed to encourage good posts, not discourage average posts. If you had RTFRules for Moderation, you would understand that.
IANAL, but I play one on
This is a good challenge. Special relativity can be explained without calculus and a five-minute explanation of its qualitative aspects is quite a reasonable expectation.
General relativity, on the other hand...
The orginal poster was correct. "Simultaneous" is meaningful in special relativity; it just depends on the reference frame. Two events in one frame are simultaneous if they occur at the same time, as measured in that frame; they're just not simultaneous in other frames. The fact that relativistic invariants (such as proper time) exist does not change the fact that there are frame-dependent concepts of physical interest (such as simultaneity, energy, momentum, etc.)
"Simultaneous" is meaningful in special relativity; it just depends on the reference frame.
I was clarifying, not disagreeing, with the simultaneous point. The definition he gave for simultaneous was basically correct well before special relativity, and didn't much change with special relativity. If you define your "dt" as being "the time from when the light emitted from when event 1 struck my eye to when the light from event 2 struck my eye", then even in classical mechanics, "simultaneous" depended on your reference frame. The difference was that previously there was always a presumption of the 'ether' frame, which was an absolute time reference, and relativity destroyed that.
So "simultaneous" really doesn't mean anything different in special relativity as it does in classical mechanics.
Proper distance, however, didn't exist before special relativity, and is very important in relativity. Two events with a timelike separation, for instance, can never be simultaneous in any frame. Two events with a spacelike separation, though, are always simultaneous in some frame.
The concept of "absolute time" really was what people thought of when they talked about "simultaneous", because they were talking about the absolute time separation between two events, and that concept really was shattered by special relativity, and that concept of "absolute time" (and "absolute spatial separation") was replaced by proper distance.
The part I (clearly) disagreed with was the part where he said that observers need to be tied to a frame for their observations to be useful. This isn't true, and it isn't the point of special relativity. The point is that things that we thought were invariants definitely weren't, but there are (new) constructions that were invariant. The "frame dependence" issue is far less important than the definition of the new frame-independent quantities, which led to quantum field theory.
From this explanation. Twin A stays on Earth and Twin B sets off in a spaceship going 0.995 c (time and space will dilate to 1/10th). He reaches a point C that is 9.995 light-years away and heads back at the same speed. Let's assume accelleration is instantaneous. When Twin B leaves earth, both twins agree their clocks read zero. When Twin B reaches point C, Twin A sees that his clock reads 10 years and Twin B's clock reads 1 year. Twin B thinks his clock reads 1 year and Twin A's clock reads 0.1 year. As soon as he turns around, Twin A still thinks B's clock reads 1 year and his clock reads 10 years, but Twin B thinks his clock reads 1 year and Twin A's clock reads 19.9 years.
Sigh, all I ever hear are bad explanations of the Twin Paradox. Let's be clear - there's no need to invoke General Relativity to explain the Twin Paradox at all. It clears a few questions up, but you still don't need it.
Here is a great explanation using only Doppler shifts, which most people understand quite easily.
The problem that you have is that you're assuming that Twin A sees Twin B reach Point C at the same time that Twin B reaches point C - he doesn't!
From Twin A's frame, he sees Twin B leave at year 0. He calculates twin B arrive at point C at year 10, but he can't see twin B arrive at point C until the year 19.995, because any light signal from point C won't arrive at Twin A before then! Amazingly enough, in the 0.005 years before Twin B arrives home, all of the images of Twin B for his entire trip home arrive all in a bunch! They're all massively blueshifted!
So Twin A sees an outbound leg that took 19.995 years for all of the images to arrive, and an inbound leg that took 0.005 years to arrive. For Twin B, this isn't true - for the outbound trip, he sees Twin A age at 1/10 the speed, and when he arrives at Point C, he's only seen Twin A age 0.1 years. On the way back, however, Twin B will see Twin A age just as rapidly as Twin A sees Twin B age in the last 0.005 years - but he'll see it for an entire year! So Twin A ages far beyond Twin B, and they will both agree that Twin A is older.
There's a terrific spacetime diagram showing this here.
Well, gravity is not acceleration, but spacetime curvature. The actual equation is G = 8*pi*T, where G is the Einstein tensor and T is the stress-energy tensor. Since G relates to geometry (the Reimann curvature tensor + Ricci scalar), this directly relates mass-energy (T) to curvature (G).
The curvature of a section of space is defined by its metric. (A metric can be thought of as the generalization of the dot product between two vectors in some space, which therefore relates the two vectors in either a coordinate-free or coordinate basis.) In simple cases we assume space is flat by using the Minkowski metric, which defines simple Lorentz transforms, which can be thought of as rotations from one frame of reference to another.
In complicated cases, space is curved, in which case we use manifolds to describe the topology of space. Topology means that a cofee cup and a donut are identical mathematical objects; manifolds mean that our topology is locally flat, so that we can use the same Minkowski machinery for local points at given spacetime coordinates. The price is we must now use tensors to "rotate" from one frame of reference to another.
You tell if space is curved or flat by its geodesic, which is simply the minimum distance between two points. In flat space it is a line; in curved space it is a curve, which you can measure by defining the geodesic deviation between two neighboring paths. At this point the normal notion of derivative, tangent, and vector are lost, and must be redefined in terms of properties of the manifold as covariant derivatives, parallel transport, and tensors (products of n-forms).
In the example of a sphere: parallel transport is the operation of moving a vector while keeping it pointed in the same direction (preserving its inner product). If you take a vector tangent to the surface pointed north on the equator, move it up to the north pole, back down a line of longitude 90 degrees west, then back along the equator, you will notice your vector ends up in the same location but with a different direction. This difference (non-commutativity of operators) is the hallmark of curved space.
Similiarly, if you wrote a differential equation describing some physics involving these vectors, you would find that it wouldn't hold under the operation described above. But if you replace your derivative operator with a covariant derivative operator satisfying linearity, Leibnitz rule, and other properties, such an equation would hold in all frames of reference.
General relativity is a local theory; it discusses the properties of spacetime at a point, where it is locally flat. Acceleration is really just deviation from a geodesic sketched in spacetime. When you consider a bullet or ball fired or thrown between the two same endpoints, in the everyday frame of reference their curvatures look radically different: the ball has to arc up higher and the bullet travels faster. But if you graph not just x and z, but t in the third dimension, both have the same radius of curvature, because the path of the ball is longer than the path of the bullet through spacetime.
And by the way, you can tell the difference between gravity and acceleration by measuring the cosmic microwave background radiation. Not only that, but since we're at least approximately in a Friedman-Robertson-Walker cosmology, an absolute "cosmic time" can be defined by the evolution of some parameter (CMB, Hubble's constant, etc).
"Invincibility is in oneself, vulnerability in the opponent." --Sun Tzu
She had an interesting history.
Einstein's work was already in very simple laymen's terms. I don't know what the point is in trying to make it into braindead powerpoint.
...Il a commencé par admettre que la lumière a une vitesse constante, et en particulier que sa vitesse est la même dans toutes les directions. C'est là un postulat sans lequel aucune mesure de cette vitesse ne pourrait être tentée. Ce postulat ne pourra jamais être vérifié directment par l'expérience; il pourrait être contredit par elle, si les résultats des diverses mesures n'étaient pas concordants. Nous devons nous estimer hereux que cette contradiction n'ait pas lieu et que les petites discordances qui peuvent se produire puissent s'expliquer facilement. ...c'est que je veux retenir, c'est qu'il nous fournit une règle nouvelle pour la recherche de la simultanéité... Il est difficile de séparer le problème qualitatif de la simultanéité du problème quantitatif de la mesure du temps; soit qu'on se serve d'un chronomètre, soit qu'on ait à tenir compte d'une vitesse de transmission, comme celle de la lumière, car on ne saurait mesurer une pareille vitesse sans mesurer un temps. ...La simultanéité de deux événements, ou l'ordre de leur succession, l'égalité de deux durées, doivent être définies de telle sorte que l'énoncé des lois naturelles soit aussi simple que possible. En d'autres termes, toutes ces règles, toutes ces définitions ne sont que le fruit d'un opportunisme incoscient." (H. Poincaré, La mesure du temps, in Revue de métaphysique et de morale 6 (1898), pp. 1-13)
Einstein's work on STR is "Poincaré for dummies", Einstein's work on GTR is "Hilbert for dummies".
STR
Einstein's paper "On the electrodymanics of moving bodies" contains nothing new. It was actually Poincaré who was the first to correctly state the special theory of relativity (the transformation formulas were found by Woldemar Voigt in 1887, H.A. Lorentz in 1892, Sir Joseph Larmor and others)
In 1898, Poincaré attacks the distinction Lorentz and Larmor make between "local time" and "universal time": "Nous n'avons pas l'intuition directe de l'égalité de deux intervalles de temps. Les personnes qui croient posséder cette intuition sont dupes d'une illusion... Le temps doit être défini de telle facon que les équations de la méquanique soient aussi simples que possible. En d'autres termes, il n'y a pas une manière de mesurer le temps qui soit plus vrai qu'une autre; celle qui est généralement adoptée est seulement plus commode.
In 1902, Poincare writes there is no absolute time and no absolute space: "1. There is no absolute space, and we only conceive of relative motion; and yet in most cases mechanical facts are enunciated as if there is an absolute space to which they can be referred. 2. There is no absolute time. When we say that two periods are equal, the statement has no meaning, and can only acquire a meaning by a convention. 3. Not only have we no direct intuition of the equality of two periods, but we have not even direct intuition of the simultaneity of two events occurring in two different places. I have explained this in an article entitled 'Mesure du Temps.' 4. Finally, is not our Euclidean geometry in itself only a kind of convention of language ? Mechanical facts might be enunciated with reference to a non-Euclidean space which would be less convenient but quite as legitimate as our ordinary space; the enunciation would become more complicated, but it still would be possible. Thus, absolute space, absolute time, and even geometry are not conditions which are imposed on mechanics. All these things no more existed before mechanics than the French language can be logically said
-- Qu'est-ce que la propriété intellectuelle? It is thought control.