Posted by
michael
on from the close-only-counts-in-horseshoes dept.
DrBlake writes "New York Times has an article about a study of Einsteins theory of relativity that I found very interesting. Not only might the speed of light be relative under certain circumstances, the famous equation E=mc2 might not be entirely correct."
Even if he was off..
by
OmniVector
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· Score: 4, Insightful
It still answered some questions and anomolies about the universe and changed the way we think about the world.
-- - tristan
E=M*c^2 story.
by
Anonymous Coward
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· Score: 4, Informative
The New York Times Sponsored by Starbucks December 31, 2002 E and mc2: Equality, It Seems, Is Relative By DENNIS OVERBYE
Roll over, Einstein.
In science, no truth is forever, not even perhaps Einstein's theory of relativity, the pillar of modernity that gave us E=mc2.
As propounded by Einstein as an audaciously confident young patent clerk in 1905, relativity declares that the laws of physics, and in particular the speed of light -- 186,000 miles per second -- are the same no matter where you are or how fast you are moving.
Generations of students and philosophers have struggled with the paradoxical consequences of Einstein's deceptively simple notion, which underlies all of modern physics and technology, wrestling with clocks that speed up and slow down, yardsticks that contract and expand and bad jokes using the word "relative."
Guided by ambiguous signals from the heavens, and by the beauty of their equations, a few brave -- or perhaps foolhardy -- physicists now say that relativity may have limits and will someday have to be revised.
Some suggest, for example, the rate of the passage of time could depend on a clock's orientation in space, an effect that physicists hope to test on the space station. Or the speed of a light wave could depend slightly on its color, an effect, astronomers say, that could be detected by future observations of gamma ray bursters, enormous explosions on the far side of the universe.
"What makes this worth talking about is the possibility of near-term experimental implications," said Dr. Lee Smolin, a gravitational theorist at the Perimeter Institute for Theoretical Physics in Ontario.
Any hint of breakage of relativity, scientists say, could yield a clue to finding the holy grail of contemporary physics -- a "theory of everything" that would marry Einstein's general theory of relativity, which describes how gravity shapes the universe, to quantum mechanics, the strange rules that govern energy and matter on subatomic scales.
Even Einstein was stumped by this so-called quantum gravity.
For now, any clue would be welcome. There is very little agreement and much confusion about the possible end of relativity. "These are times when theorists are being very adventurous," said Dr. Andreas Albrecht, a physicist at the University of California at Davis. "It's hard to tell where things will go."
The avatars of new relativity have been encouraged by hints that some cosmic rays hitting Earth from outer space have more energy than normal physics can explain. But some scientists doubt that these rays exist or, if they do, that a violation of relativity is the only way to explain them.
The cosmic ray hints are not the only signs making physicists wonder about relativity. They have also been tantalized by evidence, as yet unconfirmed, from distant quasars that a fundamental constant of nature, a measure of the strength of electromagnetism known as the fine-structure constant, might have changed ever so slightly over billions of years, shifting the wavelengths of light emitted by the quasars.
The result has been a minor explosion of interest in strange relativity, with some 70 papers being published this year, said Dr. Giovanni Amelino-Camelia, a theorist at the University of Rome.
The field, while still small, is destined for at least 15 minutes of fame next year with the publication in February of "Faster Than the Speed of Light," by Dr. João Magueijo, a cosmologist at Imperial College London. The book is a racy account of Dr. Magueijo's seemingly heretical effort to modify relativity so that the speed of light is not constant, and he will promote it on a long lecture tour.
"Ruling out special relativity by 2005 is a bit extreme," Dr. Magueijo said in a recent e-mail message, referring to the coming centennial of Einstein's famous paper, "although I would be very surprised if by 2050 nothing beyond relativity has been found."
Most physicists have yet to buy into this presumed revolution. Dr. Edward Witten of the Institute for Advanced Study in Princeton, called recent arguments that some versions of quantum gravity would violate relativity "unimpressive."
Dr. Juan Maldacena of Harvard said he doubted relativity was violated in string theory -- the leading candidate for a theory of everything. "But of course," he noted, "we should always test our theories."
Dr. Carlo Rovelli, a gravitational theorist at the University of the Mediterranean in Marseille, said it was a "risky" hypothesis, "but the prize if it happened to be true is so great that it is worthwhile taking the risk of exploring it in detail."
Dr. Andrew Strominger of Harvard pointed out that Einstein himself modified relativity in 1915, when he brought gravity into the picture with his general theory of relativity. Special relativity, as the 1905 theory became known, is only strictly valid in flat space without gravity, Dr. Strominger said.
He added, "It is natural to think that Einstein's relativity will in some sense be violated by small corrections, just as Newton's theory of gravity has small corrections." These corrections did not make Newton wrong, he said, they just meant his theory was not always perfectly applicable. Likewise, relativity may give way to a more complete and accurate theory.
How relativity could break down, if it does, depends on how physics might accomplish its grand dream of quantum gravity.
Many physicists are placing their bets on string theory's mathematically imposing edifice in which nature comprises tiny strings vibrating in 10 dimensions of space-time. But this theory may play out in billions of ways, and some physicists complain that it can be made to predict almost anything.
In the late 1980's, Dr. V. Alan Kostelecky, a particle physicist at Indiana University, and his colleagues pointed out that in some of these solutions, the spins of the strings could impart an orientation to empty space, like the lines left by the weave in a fine cloth. In that case, they say, a clock oriented in one direction could tick slightly faster or slower than one oriented differently, in violation of the rules of relativity. That is something Dr. Kostelecky and his colleagues have proposed to test using ultraprecise clocks on the space station.
Dr. Kostelecky and his colleagues have constructed an extension to the standard model of particle physics that catalogs all the possible ways that relativity can be violated. Others, including Dr. Amelino-Camelia, Dr. John Ellis of CERN, Dr. Tsvi Piran of the Hebrew University in Jerusalem and the Harvard theorists Dr. Sheldon Glashow and Dr. Sidney Coleman, have attempted to study the ways that relativity can be violated by quantum gravity or in the high-energy cosmic rays.
Violation is not inevitable, Dr. Kostelecky said. "Is it plausible? Yes. Is it likely? Enough so that I've invested years of my life."
Few physicists would seem to have as much invested in revising relativity as Dr. Magueijo. In his book he describes how beginning in 1996 he cajoled Dr. Albrecht, then at Imperial, into pursuing with him the heretical notion that the speed of light had been much higher in the dim cosmic past as a solution to various cosmological puzzles. Cosmologists did not rally to the idea, which even Dr. Magueijo admitted violated relativity. His co-author, Dr. Albrecht, himself called it an idea that is "not even properly born yet," and said it needed to find roots "in some convincing physics."
In the intervening years, as a sideline to his day job as a conventional cosmologist, he and a growing number of comrades have continued to tinker with modifying relativity in a variety of ways that go under the umbrella name of V.S.L., for variable speed of light theories.
In the science world, the book might attract attention for its jaunty and irreverent style as well as for its content. "What the hell, it's only Einstein going out of the window . ..," he writes in one passage. In others he describes the editor at a prominent journal as a moron, his bosses at Imperial as pimps and the rival quantum gravity camps as cults.
Asked how he expected his colleagues to react to the book, he answered, "It wasn't written for them; it was written for the public." He called it "a very honest view of how scientists feel," adding, "It's the language I use normally."
The main motivation for considering V.S.L. theories, Dr. Magueijo explained, comes from the as-yet undiscovered quantum gravity. In relativity there is only one special number, the speed of light, but in quantum gravity, he explained, there is another special number, known as the Planck energy, equivalent to 1019 billion electron volts. According to quantum gravity thinking, an elementary particle accelerated to that energy will behave as if space and time themselves are lumpy and discontinuous and all the forces of nature are unified.
According to relativity, however, Dr. Magueijo explained, differently moving observers could disagree on how much energy the particle had and thus whether it was displaying quantum gravity effects or not. In short, they would disagree on what the laws of physics were.
"Perhaps relativity is too restrictive for what we need in quantum gravity," Dr. Magueijo said. "We need to drop a postulate, perhaps the constancy of the speed of light."
The most recent buzz in V.S.L. circles is about something called "doubly special relativity." In 2000, hoping to fix the cosmic ray problem, Dr. Amelino-Camelia proposed modifying the rules of relativity so that there would be a limit to the momentum that any particle could have, just as now there is a limit to the velocity.
Subsequently Dr. Magueijo and Dr. Smolin of the Perimeter Institute proposed their own doubly special version in which there is a limit to the amount of energy that an elementary particle can attain, namely the so-called Planck energy, at which the forces are unified and quantum gravity effects dominate.
One casualty of this tinkering, the V.S.L. scientists agree, will be everyone's favorite formula, E=mc2, to be replaced by a more complicated, cumbersome equation that Dr. Magueijo reproduces in his book.
A mark of all the doubly special theories, Dr. Magueijo said, is that the speed of light will vary with its color, with higher frequencies and energies going slightly faster than lower ones. That might manifest itself in observations of gamma ray bursters, distant gargantuan outbursts by an upcoming NASA satellite called Glast (gamma ray large area space telescope), scheduled for launching in 2006.
The theory also predicts that light should slow down near massive objects and actually come to a stop at the end of a black hole, preventing anything from entering that dark gate, Dr. Magueijo said in his book. In principle the effect, he said, could be tested by spectroscopic measurements of the light emitted from dense objects like neutron stars.
To some physicists, however, the very idea of variations in the speed of light in a vacuum -- the c in E=mc2 -- is meaningless. The miles and seconds by which speed is measured are human inventions, they point out, defined in fact in terms of lightwaves, so the whole notion of the speed of light varying is circular. In the last analysis, they point out, all physical measurements boil down to a few dimensionless constants like the fine structure constant, alpha. "What we measure objectively is whether alpha varies," said Dr. Michael Duff of the University of Michigan in an e-mail message.
Dr. Magueijo said those criticisms were technically correct but said the speed of light was one factor of several in the formula for alpha. So if alpha varied, as some astronomical measurements have suggested, one could choose to think of it as a variation in the speed of light, of electric charge, or even a variation in another number known as Planck's constant -- or all three -- if that made the math simpler. "It's a matter of convention," he said, adding, "you make the simplest choice."
Despite all the activity, scientists agree that they are mostly in the dark about the deeper consequences of these conjectures. "Some may eventually be developed to the point of being a credible alternative to relativity," conceded Dr. Kostelecky, saying that he suspected that others might not really change relativity or might have already been excluded by existing experiments. Without a systematic analysis it was impossible to know.
Dr. Amelino-Camelia said that the doubly special theories preserve Einstein's principle that all motion is relative, but at an unknown cost to the rest of physics."We paid a dramatic price for relativity: the notion of absolute time," he said. "This time it is not completely sure what is the axiomatic principle we have to give up."
Dr. Albrecht urged caution and said physicists needed guidance from experiments before tossing out beloved principles like relativity. "The most dignified way forward," he said, "is to be forced kicking and screaming to toss them out."
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No = Registration*link^2
by
Anonymous Coward
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· Score: 5, Informative
That's the paradox...
by
starsong
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· Score: 5, Informative
...and the beauty of special relativity.
They key thing is that the speed of light is fixed relative to *everything*. This means that if I'm standing by the highway and measure it, I get the same speed as a person in a car going 60 mph away from me. And since the speed of light is fixed, everything ELSE distorts to make up for it. That includes time (time dilation) and space (Lorentz contraction). It leads to some pretty freaky and amazing consequences.
Re:That's the paradox...
by
Trogre
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· Score: 5, Informative
A good way to observe (well, simulate) some of these effects is to download lightspeed and have a play. Effects such as Lorentz contraction, doppler shift, headlight effects and optical aberrations can be observed. Very cool with the add-on Starship Voyager model.
There's also some very nice mpegs floating around the net of tram cars and flashing lamp posts in a world where the speed of light is slowed to a couple of meters per second. Now if only I could dig up the URL...
-- "Nine times out of ten, starting a fire is not the best way to solve the problem." - my wife
well, of course...
by
QID
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· Score: 5, Informative
E=mc^2 is actually a simplified form of the real equation, E=mc^2/sqrt(1-v^2/c^2). A convenient graphical depiction can be found in a few seconds with google, or here: http://www.btinternet.com/~j.doyle/SR/Emc2/Derive. htm.
This story's at the top of the page, and look what's at the bottom:
186,000 Miles per Second. It's not just a good idea. IT'S THE LAW.
Re:Coincidence...?
by
Dirtside
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· Score: 4, Funny
186,000 Miles per Second. It's not just a good idea. IT'S THE LAW.
Actual mileage may vary.
-- "Destroy science and religion. Science would re-emerge exactly the same; but not religion." - Penn Jillette, paraphrased
Re:gravity effects are instantaneous
by
rsidd
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· Score: 5, Informative
Wrong. Newtonian gravity suggests effects should be instantaneous, that's why Einstein knew it was wrong and came up with the general theory of relativity, which is the best theory of gravity we have today (and unlike special relativity which was built on the work of others, GR was Einstein's own, nobody else was even thinking along those lines.)
As for magnetism, that travels at the speed of light -- that has been known since Maxwell's time. Basically, that's what electromagnetic radiation is: a changing magnetic field causes a changing electric field, which causes a changing magnetic field,.... The paradox was that Maxwell's equations give you a constant for the speed of light, without reference to the velocity of the observer, so people assumed that they are valid only in the rest frame of a mythical "ether". Einstein showed that Maxwell's equations are correct for all observers, and it is Newton's/Galileo's ideas which are wrong.
Incidentally, just like electromagnetic radiation, GR implies that gravity waves should exist too.
Even if his theories are improved
by
backslashdot
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· Score: 4, Insightful
He will still be a great physicist that helped bring us to where we're at in science today.
I dont see the big deal in "disproving" him. It's sad that people will take some sort of glee in thinking "Ha! Einstein was wrong!" Einstein himself would be glad to see people come closer in figuring out the natuer of the universe.
Given the knowledge and tools available to him at the time, its amazing he came up with something in 1904 that people nearly 100 years later are still trying to figure out how to improve or disprove. Today we have the advantage of knowing how to look at things the way he did.
Einstein's abilities, creativity, and ideas will have a permanent influence on humanity's acheivements.
Re:can someone explain to me
by
rossifer
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· Score: 5, Interesting
c is relative to the observer, no matter which observer we're talking about. Anything that can measure the speed of a photon will always measure it going at the speed of light through that substance. Through a perfect vacuum, it's c. Through space it's c - epsilon (epsilon is an infintesimally small number). Through water it's about c/1.335.
If you are zooming past me at half the speed of light and both of us measure the speed of a particular photon at the same time, we'll both measure it's speed as c. What will be different about our two measurements is that you'll see a higher energy photon (bluer) than me if the photon is moving opposite to your motion relative to me and a lower energy photon (redder) if the photon is moving in the same direction as your motion relative to me.
No particular point in space is special. Once you identify where the observer is located, you can call that point in space an "origin" or "zero" and make all of your measurements from that point in space. The rest of the universe relative to that origin is called an "inertial reference frame", but it's just the same as any other reference frame. There's another trick. Behavior of things in inertial reference frames is time dependent because gravity pulls your frame around and changes everything around it slightly every moment. Besides that, two inertial reference frames may have a relative velocity but for a moment share the same point in space (the example above).
That's when tensor math starts to come in handy. Don't worry, I won't torture you with that.
Relativity, once you grok it, will bend your mind. From a metaphysical perspective, it emphasizes the reality that most of what we call facts are actually just high probability observations.
Remember, there is no spoon.
Regards, Ross
You misunderstand completely
by
kfg
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· Score: 4, Insightful
The more we learn where our knowledge is incorrect the more *correct* it becomes. The job of the scientist is thus to question *everything.*
The very thing that shakes your faith in our knowledge is the very thing that *strengthens* our knowledge.
Think about it.
KFG
Re:You misunderstand completely
by
Hektor_Troy
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· Score: 5, Funny
The job of the scientist is thus to question *everything.*
Why?
-- We do not live in the 21st century. We live in the 20 second century.
Re:You misunderstand completely
by
lars_stefan_axelsson
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· Score: 5, Informative
I don't mean to be a troll, but I really want to ask this. Why is it so frowned upon to question evolution?
By the nature of science, it is granted that theories and current "knowledge" may be overturned in light of future counter-evidence. However, evolutionists give the impression that they consider their views to be rock-solid, indisputable Truth that is impossible to disprove now and forevermore. Anyone who dares to disagree is dismissed out of hand as a kook. (See, I had to post as AC to even ask.)
Well, I don't know if it's really the case that evolutionists consider their views to be a "truth that is impossible to disprove" etc. (at least not the scientfically minded ones, for any theory there are supporters that one could do without).
Now let me start by saying that I'm not really an expert on evolution, since I'm european I've never had to be. There are no creationists here to speak of, and hence I'm not well versed in their way of thinking. I am a "scientist" however, so I'm somewhat qualified to speak about that.
Now, not to write an essay answering your question, but much of it boils down to what we mean by "wrong." First some preliminaries though. The strength of any scientific theory rests on its predictive powers, how well does it foresay and explain the outcome of experiments or observations (past of future). Any good scientific theory then is very specific (or strong), what we like to call "easily falsifiable", i.e. it is simple to detect when its predictive powers are failing. (Hence many of them in the natural sciences are formulated in some form of logic; "mathematics" since that provides for a stronger statement to be made). So, strong theory equals "easy to prove wrong" given contradictory evidence.
Now, then what does it mean to be "wrong" in the scientific sense? In short it's when there are observations made that cannot fit into the current theory. A prime example would be Newton's law of kinetic energy E=1/2mv^2. For a long time that was thought to be all there is to it, and all the experiments and observations that could be made corroborated that. Today we know that it's not "true". It's OK for lower speeds, but it completely fails to take relativistic effects into account (see previous posts in this thread), and hence has been relegated to the scrap heap of scientific theories, right?
Well, not quite. It's still a very good approximation for most macroscopic real world phenomena. It still explains them very well, and even post Einstein, it hasn't really lost any of it's predictive powers in the domain in which it was thought up. So even though it may now be thought "wrong" in the strictest sense of the word; it may not tell all of the truth to all people, it's still a pretty darn good theory if you're a bit more careful with it's application.
This is also true of Darwinian evolution. It's a very well tested theory (or "fact" if you will) by now, with wast predictive and explanatory powers. Any later theory that superseeds it must still explain all the observations with the same (or better) accuracy as Darwinistic evolution has to date. So even though evolution as a theory may be proven "wrong" at a later date, it'll still be mostly "right." As Newtons' laws still are.
Now, in order to completely close the sack, we also need Occam's razor. I.e. given two equally predictive theories, we prefer the simpler one. It's really a common sense argument. Why make things harder than they have to be. It's also the only scientific loophole that creationists can exploit. By invoking a "deus ex machina" in the form of an omnipotent God, that stacks the deck so that scientists cannot make correct observations (or make them correctly), you can of course invalidate any and every theory. And that's why science doesn't deal with that. If someone stacks the deck, we won't play! (Then we can continue various philosophical arguments, and in doing so rapidly leaving the natural sciences.)
And that's incidentally why science isn't "just another religion", science specifically is about absolutely minimising the things that have to be taken on faith (such as the existence of the rest of the world etc), while religion(s) are about systematising the things you take on faith. Often that means that science cannot say very much on a subject, and people having a natural tendency towards taking things on faith, often over interprets scientific statements (it takes practice to so thoroughly disiplining your subjectiveness as the scientist must do). This leads to "scientific" statements or belif in the general public, that really aren't. But that's not the fault of science, more a fault of the schooling system.
If you're specifically interested in evolution, I have it on good authority that you could do worse than studying talk origins. I haven't got any good references on the philosophy of science in english for you, but I'm sure that a few minutes of googling will turn up a multitude.
-- Stefan Axelsson
Re:You misunderstand completely
by
jaoswald
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· Score: 5, Insightful
Did you actually read the link you included from talkorigins.org? It contains a plausible sequence of evolutionary changes that would lead to the bombardier beetle; exactly what you claim is impossible.
In any case, argument from design doesn't provide any "explanation," much less a better one. How did the designer make the beetle, and all its close genetic relatives, where none had existed before? Why the variety of mechanisms in the close relatives, instead of a single design?
Re:You misunderstand completely
by
NoMoreNicksLeft
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· Score: 5, Insightful
Actually, nobody has ever seen "evolution" happen in a way congruent with the theories proposed by Darwinian evolutionists. Their theories include rates of change that are so slow as to be unobservable.
Wrong. We also can't see electrons, or stars/galaxies at the edge of the universe. We don't need to see them to observe them though. Evolution has been observed in the fossil record, and even to some extent in the laboratory. Still, the lab observations are fairly new (the last 30-40 years) and science is busy debating whether or not it is indeed evolution... after all, as you pointed out, it is a slow effect.
Furthermore, no evolutionist has ever explained creatures like the Bombardier Beetle and its built-in flame thrower.
Huh? Of course evolutionists don't know everything at once... they don't claim to be omniscient. However, that doesn't mean they are doofuses without a clue. There have already been several possible explanations suggested in the scientific community, and no one disputes that something unknown is going on. You must not be researching this issue very thoroughly, if you believe there are no explanations at all, and that biologists are all sitting around dumbfounded.
Some of the more radical ideas center around the possibility that DNA acts more like a computer than a raw blueprint. That it might "store" a bunch of "mutations", saving them for a rainy day when some threshhold is reached. This "computer" might even span many individuals in the population. So instead of a gradual change into a "bombadier beetle" where there are many transitionary variants doomed to blowing themselves up, evolution simply "skipped over" those and went straight to the version capable of blowing up its enemies, and not itself.
Was it Greg Bear that said "Even evolution is evolving, becoming better at what it does." ?
Besides, lay off Darwinian evolution. Most people today see it as only the crudest approximation of the reality of evolution. Would figure that a bible thumper would be reacting to the scientific community of 100 years ago... you guys are always more than a few steps behind.
Comment removed
by
account_deleted
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· Score: 4, Informative
Comment removed based on user account deletion
Re:Light Speed Relative?
by
Jordy
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· Score: 4, Informative
A blackhole warps space and time around it. Light travels in a straight line, but since the space it is traveling over is warped, it enters the black hole.
The light itself does not speed up or slow down. From outside the blackhole, light is moving away from an observer at the speed of light. From inside the blackhole, light is moving towards you at the speed of light.
You have to remember that "speed" is a function of distance and time. Time is not constant, but from any frame of reference (you for instance) however, the "speed" of light is.
-- The world is neither black nor white nor good nor evil, only many shades of CowboyNeal.
I'm sorry, but this is entirely incorrect.
by
kfg
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· Score: 4, Informative
The fact that light is in orbit has *no* effect on its speed. You're thinking of light as a Newtonian object getting "sucked into" the black hole. Light isn't "sucked in." The escape velocity of the black hole is simply higher than the speed of light and the light follows a ballistic trajectory. . . at * the speed of light.*
Light is not Newtonian. It dosn't "speed up" as it falls, or "slow down" as it rises. That's kind of the point. Try working some simple Lorentz Transformations to begin to get a feel for this.
KFG
Re:PLEASE torture me with that!
by
Aleatoric
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· Score: 4, Informative
I'll let someone else torture you with tensors:o)
Here are three (of many) links that I've found in the past that deal with relativity and provide varying degrees of rigor and completeness in the explanations.
How stuff works! Talking about special relativity: http://www.howstuffworks.com/relativi ty.htm
A pretty interesting and more rigorous explanation: http://physics.syr.edu/courses/modul es/LIGHTCONE/
And finally, a question and answer format explanation:o) http://www.sciencenet.org.uk/database/Physics /List s/relativity.html
This should get you a good set of basic coverage about relativity.
--
Nunc Tutus Exitus Computarus.
Re:can someone explain to me
by
GMFTatsujin
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· Score: 5, Insightful
Lordy... You don't ask much, do you?
The speed of light is constant in all possible frames of reference, according to Einstein. Basically what he's saying is that for any two objects at rest relative to each other (regardless of their motion to the rest of the universe, they appear not to be moving to *each other*), time and space behave in the same way. The beauty of his theory is that no one object can be said to be at universal rest to everything else -- there is no universal frame to measure against. Therefore, every frame of reference is valid and will behave the same way. This kills Ether theory dead, since Ether theory depends on a universal frame of reference. If it didn't have a universal frame of reference, then space and time would start behaving oddly within your *own* frame of reference depending on your motion. This is not the case - the light on Pluto behaves the same way as the light on Earth, even though the two are moving in different frames.
It's only when you introduce out-of-frame references (I'm standing still, the train is moving at 60mph away from me) that relativity kicks in and the laws start to behave weirdly.
Not inconsistantly, just weirdly. It's all in shifting your viewpoint.
The trick with light is to realize that although it travels at the same speed in every frame of reference, the *wavelength* is what changes between frame. This is what that whole red-shifting/Doppler effect is about. The speed of light is constant; the color, however, changes depnding on your frame of reference. If you shoot a blue light at me while we're both standing still relative to each other, it looks blue to me. If I run away *really fast*, it will still be blue to you, but it will appear red to me because the wavelength alters even though it still travels toward me at a constant rate. Ditto if *you* run away from me - the light is blue to you, but again, it appears red to me, even though it travels at the same speed.
Light does not behave in the Newtonian way - acceleration does not effect its speed, only its wavelength. That's where the question of why light is constant to everything, even moving objects, is answered.
Weird, huh?
For a far, far, better explanation (and a fantastic grounding on String Theory in terms for non-physicists) check out The Elegant Universe by Brian Greene. If I could, I'd give this book a Pulitzer every year until the day I died.
Re:so if two objects are traveling toward the same
by
lirkbald
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· Score: 4, Informative
point at c/2 from opposite directions they both gain infinite mass!? Nope. Drop all your newtonian physics assumptions out the window. Speed is relative as well, and doesn't add in such a straightforward fashion. An observer on one object will actually measure the velocity of the other as something less than c. (pardon me if I don't go look up the exact equations right now). That's where relativistic time dialation comes from- time has to slow down to make up for the non-additive properties of velocity.
By that same argument if I am traveling at c toward Earth, Earth gains infinite mass and the gravitational pull drags me toward it even faster! Wrong again. You can't travel at c toward earth, so the question is meaningless. It takes infinite energy for a massive to reach that velocity, so it's impossible.
No offense, but this makes no sense. Either none of us understand it, or the emporor has no theory. Quite a bit of offense taken, actually. You missed the third possibility, that *you personally* don't understand it, and that physicists do. Do you really think that points as obvious as yours would have been missed in all the years that Relativity has been under close scrutiny?
Oh, well. People who argue "I don't get it, therefore it's wrong" annoy me.
Einstein knew he was wrong
by
automatic_jack
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· Score: 5, Informative
Not more than a few year's after developing his theories of general and special relativity, Einstein realized that they weren't perfect. The simple reason behind his realization was that the theories of relativity didn't make sense when applied on a quantum scale, and the theories of quantum physics didn't make sense when applies of a relative scale. Einstein refused to believe that the universe worked in such a way that there had to be two mutually exclusive theories to explain physics on the very small and the very large scale.
Of course, the rest of the world was busy experimenting with his theories of relativity, but after he published them he quickly lost interest in their progress. He spent the rest of his life searching for what he referred to as the "unified field theory," a single theory that could properly explain quantum physics and relativity at the same time.
I'm not a physicist by any stretch of the imagination, but theoretical science does interest me. Brian Greene's book, The Elegant Universe does a great job of explaining the background on this. It's worth a look.
--
--
Have you ever noticed that at trade shows, Microsoft is always the company that is handing out stress balls?
I hate to say this...
by
dasunt
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· Score: 4, Funny
But why do you think that your brain is capable of understanding the basic forces of the universe?
Your brain evolved to keep you away from things that want to eat you, find things you want to eat, and basically preserve you until you could insure that you have spread your genes. Last time I checked, understanding the basic rules of reality wasn't needed to ensure that you live long enough to breed.
Hell, we'er just lucky that the same math that works on our scale also seems to work when we look at how the universe works.
Even now, logic has begun to fail us when we ask the deep questions. Consider this: What made this reality? Oh sure, I know the theories that suggest that this universe might have been created by another universe, and at this level, cause and effect goes out the window, leading to the possibility that this universe can create the ancestor of the universe that created it, but what allowed this gestalt to exist?
There's an Heinleinian phrase that occasionally gets said on slashdot: There ain't no such thing as a free lunch (TANSTAAFL). Too bad that its wrong, since the universe is the biggest example of a free lunch in action.
[ Don't feel so bad - my brain also seems hellbent to make me survive long enough to ensure my genes are passed on. Damn thing is that my body agrees with it and is planning to expire in half a century in order to free up resources for my future offspring. Its a comspiracy, I tell you... ]
Just my $.02
That's not exactly true...
by
jpmorgan
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· Score: 4, Informative
It's not exactly true that we have no clue what string theory's predictions are.
On one hand, the formulations of string theory are Very Hard (TM). I'm sure you think youv'e seen hard math, but there's hard math and there's string theory math. Classic standard model quantum mechanics and general relativity is hard math, nice hard partial differential equations to solve. String theory math makes this look easy though. It's so hard that nobody has yet even formulated the exact equations - everybody's working with approximations. So the predictions that people are making with string theory may not be completely accurate, as they aren't working from the real threory, just an approximation of it. Nice, eh?
On the other hand, most of the quantitative predictions that string theory does generate are mindboggling hard to test anyway, since in almost all respects string theory agrees with classic quantum mechanics (there's an oxymoron...) until you get to some pretty insane energies (think plank energy).
Fortunately, recently a few physicists have come up with some more subtle qualitative predictions that should prove feasible to test (for example, string theory predicts that cosmic microwave background radiation should be pixelated - the big bang didn't do antialiasing:).
What is C relative to?
by
DesScorp
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· Score: 4, Funny
Dude......C is relative to B. It's C++ and Java that's relative to C. Cobol is a different species altogether.....
-- Life is hard, and the world is cruel
Re:FTL == Time Travel ?
by
Soft
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· Score: 5, Interesting
I have been told that theory forbids any travel faster than light, no matter what the means ("warp drive", "hyperspace", "teleporter", whatever). My understanding is that if you could, some observers would see you traveling back in time, and this is forbidden.
Yes. One of the hypotheses of relativity is causality, that is, one event can possibly cause another only if the latter occurs at a later time than the former, and this must hold true for all possible observers whatever their frame of reference.
Now, as you know, the passing of time for an observer varies with his frame of reference (his speed, to put it simply). Hence, given two events, the interval of time from one to the other will not be the same for all observers. But if one is to cause another, it must always remain in its past; the sign of the time difference "t2-t1" must not change whatever the observer.
Unfortunately, my memories of relativity are too scarce to put this into equations, but if you could travel faster than light, you could, say, watch an asteroid smash into the Earth and warn your friend on the Centauri stock market to sell shares of all Terran businesses before anyone could "see" the flash of the impact.
And in a given frame of reference (maybe that of a traveler aboard a STL ship in-between), it would look as if you knew about it before it happened; stretching it further, it would be possible for the traveler (maybe through another FTL "jump") to warn Earth before the impact. Bye-bye causality.
If these situations are not to happen, information must not travel FTL.
Thanks for a good post. --I offer the following not as a criticism in any way, but just as a thought which has been bouncing around in my mind looking for an excuse to be expressed.
First off, I'm not a creationist. Indeed, I find that whole debate to be entirely infernal, as both sides seem to me quite flawed in their own ways. That being said. ..
Occam's Razor bugs me. As a deductive tool, it is a pretty good one; it works for the most part. What I find unsettling, however, is that it seems to have become, thanks to its presentation and treatment in popular media, understood and accepted by many as a de facto scientific law when it is not.
It is a rule of thumb, and only a rule of thumb. --It is only a rule of thumb, because it is not always right. Every time something unexpectedly complex turns out to be the reality behind a phenomenon which might otherwise have been explained through simple means, Occam's Razor is blunted.
Example:
When Alexandre Graham Bell first announced to the world that he had discovered a way to send a voice signal over a wire, the world erupted with both excitement and disbelief. One major newspaper even ran a story written by experts which attempted to debunk Bell's claim. They used diagrams demonstrating that sound waves sent down thin metal tubes of the diameter Bell was using for wires, could not possibly travel the kinds of distances he claimed. The experts were engineers well versed in the science and dynamics of sound as employed in the kinds of voice communication pipe systems once used large ocean going vessels. To the writers of the article, they were being entirely reasonable.
"Which is more likely?" they must have asked themselves, "That Bell has created some magical new invention to send sound along miles of very thin tubes? Or that he is lying?"
Occam's Razor is deeply rooted in how one perceives, how much information there is available to work with, and what has been previously accepted by culture as normal and/or outlandish.
-Now Bell was, of course, proven to be right. When words crackled out from crude speakers for all to hear, the enthusiastic debunkers, (and there is never any shortage of enthusiastic debunkers or respected, conservative media outlets to give them a voice and print their diagrams), had to quietly go mum and withdraw their objections. But that was in part due to large forces which wanted and allowed Bell to be proven right. If you don't advertise a fact or discovery, facts and discoveries can easily vanish. People have short memories. People have short lives. Without active perseverance, knowledge is a self-burying commodity until it becomes large enough to self-sustain, and even then, it is not so very difficult to forget important turns of history after only a few fickle generations have passed.
Science as a concept, is a pure, wonderful thing, but it does not know everything. Indeed, many institutions are not so pure as the science which they employ; it is well known that individuals with weak morals, and corrupt institution will suppress data, twist data and even make up data on a basis regular enough that the public pool of knowledge has been polluted to the point that the employment of Occam's Razor is by no means reliable in today's arena of public thought.
Just something to consider next time you feel the need to slam a new idea. Remember that Occam gave us a deductive tool, not an irrefutable law.
-Fantastic Lad
Examine your assumptions
by
naasking
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· Score: 4, Interesting
What makes you think there even was a beginning? Keep in mind that we have never actually seen the beginning of an event and the end; those boundaries are imposed by us. Reality is really a continuous cascade of effects which themselves become causes. How do we know there even is a beginning to the universe?
E=mc^2 is actually a simplified form of the real equation, E=mc^2/sqrt(1-v^2/c^2).
Please don't forget your subscripts! As everyone learns in basic special relativity, total energy, which is kinetic + potential, is
E = m0 * c^2 * gamma,
where gamma = 1 / sqrt( 1-v^2/c^2 ) and m0 is the rest mass.
At v = 0, gamma = 1 and E = m0 c^2, Einstein's famous formula for rest energy. Kinetic energy is given by KE = E - m0 c^2, or
KE = m0 c^2 ( gamma - 1 ).
To see any appreciable effect of velocity, consider the situation where you are going fast enough to double your effective mass (gamma = 2). Solving for velocity gives v = c sqrt(3/4) = 86.6% of the speed of light. Not gonna happen with current technology (outside of atom smashers).
As v -> c, gamma -> infinity and this is Einstein's rationale for saying it's impossible to accelerate any matter up to the speed of light, since doing so would require an infinite amount of kinetic energy. On the other hand, the formula for photons is
E = p c = h c / lambda = h nu,
where p is momentum, h is Planck's constant, lambda is wavelength, and c / lambda = nu is the frequency. Since photons are never at rest (remember the constant speed of light?), you won't see any m's make an appearance here. And just for the record, this last formula explains the photoelectric effect, which is what won Einstein his Nobel, not E = m c^2.
-- This post expresses my opinion, not that of my employer. And yes, IAAL.
Slashdot Mirror
It still answered some questions and anomolies about the universe and changed the way we think about the world.
- tristan
The New York Times Sponsored by Starbucks
.," he writes in one passage. In others he describes the editor at a prominent journal as a moron, his bosses at Imperial as pimps and the rival quantum gravity camps as cults.
December 31, 2002
E and mc2: Equality, It Seems, Is Relative
By DENNIS OVERBYE
Roll over, Einstein.
In science, no truth is forever, not even perhaps Einstein's theory of relativity, the pillar of modernity that gave us E=mc2.
As propounded by Einstein as an audaciously confident young patent clerk in 1905, relativity declares that the laws of physics, and in particular the speed of light -- 186,000 miles per second -- are the same no matter where you are or how fast you are moving.
Generations of students and philosophers have struggled with the paradoxical consequences of Einstein's deceptively simple notion, which underlies all of modern physics and technology, wrestling with clocks that speed up and slow down, yardsticks that contract and expand and bad jokes using the word "relative."
Guided by ambiguous signals from the heavens, and by the beauty of their equations, a few brave -- or perhaps foolhardy -- physicists now say that relativity may have limits and will someday have to be revised.
Some suggest, for example, the rate of the passage of time could depend on a clock's orientation in space, an effect that physicists hope to test on the space station. Or the speed of a light wave could depend slightly on its color, an effect, astronomers say, that could be detected by future observations of gamma ray bursters, enormous explosions on the far side of the universe.
"What makes this worth talking about is the possibility of near-term experimental implications," said Dr. Lee Smolin, a gravitational theorist at the Perimeter Institute for Theoretical Physics in Ontario.
Any hint of breakage of relativity, scientists say, could yield a clue to finding the holy grail of contemporary physics -- a "theory of everything" that would marry Einstein's general theory of relativity, which describes how gravity shapes the universe, to quantum mechanics, the strange rules that govern energy and matter on subatomic scales.
Even Einstein was stumped by this so-called quantum gravity.
For now, any clue would be welcome. There is very little agreement and much confusion about the possible end of relativity. "These are times when theorists are being very adventurous," said Dr. Andreas Albrecht, a physicist at the University of California at Davis. "It's hard to tell where things will go."
The avatars of new relativity have been encouraged by hints that some cosmic rays hitting Earth from outer space have more energy than normal physics can explain. But some scientists doubt that these rays exist or, if they do, that a violation of relativity is the only way to explain them.
The cosmic ray hints are not the only signs making physicists wonder about relativity. They have also been tantalized by evidence, as yet unconfirmed, from distant quasars that a fundamental constant of nature, a measure of the strength of electromagnetism known as the fine-structure constant, might have changed ever so slightly over billions of years, shifting the wavelengths of light emitted by the quasars.
The result has been a minor explosion of interest in strange relativity, with some 70 papers being published this year, said Dr. Giovanni Amelino-Camelia, a theorist at the University of Rome.
The field, while still small, is destined for at least 15 minutes of fame next year with the publication in February of "Faster Than the Speed of Light," by Dr. João Magueijo, a cosmologist at Imperial College London. The book is a racy account of Dr. Magueijo's seemingly heretical effort to modify relativity so that the speed of light is not constant, and he will promote it on a long lecture tour.
"Ruling out special relativity by 2005 is a bit extreme," Dr. Magueijo said in a recent e-mail message, referring to the coming centennial of Einstein's famous paper, "although I would be very surprised if by 2050 nothing beyond relativity has been found."
Most physicists have yet to buy into this presumed revolution. Dr. Edward Witten of the Institute for Advanced Study in Princeton, called recent arguments that some versions of quantum gravity would violate relativity "unimpressive."
Dr. Juan Maldacena of Harvard said he doubted relativity was violated in string theory -- the leading candidate for a theory of everything. "But of course," he noted, "we should always test our theories."
Dr. Carlo Rovelli, a gravitational theorist at the University of the Mediterranean in Marseille, said it was a "risky" hypothesis, "but the prize if it happened to be true is so great that it is worthwhile taking the risk of exploring it in detail."
Dr. Andrew Strominger of Harvard pointed out that Einstein himself modified relativity in 1915, when he brought gravity into the picture with his general theory of relativity. Special relativity, as the 1905 theory became known, is only strictly valid in flat space without gravity, Dr. Strominger said.
He added, "It is natural to think that Einstein's relativity will in some sense be violated by small corrections, just as Newton's theory of gravity has small corrections." These corrections did not make Newton wrong, he said, they just meant his theory was not always perfectly applicable. Likewise, relativity may give way to a more complete and accurate theory.
How relativity could break down, if it does, depends on how physics might accomplish its grand dream of quantum gravity.
Many physicists are placing their bets on string theory's mathematically imposing edifice in which nature comprises tiny strings vibrating in 10 dimensions of space-time. But this theory may play out in billions of ways, and some physicists complain that it can be made to predict almost anything.
In the late 1980's, Dr. V. Alan Kostelecky, a particle physicist at Indiana University, and his colleagues pointed out that in some of these solutions, the spins of the strings could impart an orientation to empty space, like the lines left by the weave in a fine cloth. In that case, they say, a clock oriented in one direction could tick slightly faster or slower than one oriented differently, in violation of the rules of relativity. That is something Dr. Kostelecky and his colleagues have proposed to test using ultraprecise clocks on the space station.
Dr. Kostelecky and his colleagues have constructed an extension to the standard model of particle physics that catalogs all the possible ways that relativity can be violated. Others, including Dr. Amelino-Camelia, Dr. John Ellis of CERN, Dr. Tsvi Piran of the Hebrew University in Jerusalem and the Harvard theorists Dr. Sheldon Glashow and Dr. Sidney Coleman, have attempted to study the ways that relativity can be violated by quantum gravity or in the high-energy cosmic rays.
Violation is not inevitable, Dr. Kostelecky said. "Is it plausible? Yes. Is it likely? Enough so that I've invested years of my life."
Few physicists would seem to have as much invested in revising relativity as Dr. Magueijo. In his book he describes how beginning in 1996 he cajoled Dr. Albrecht, then at Imperial, into pursuing with him the heretical notion that the speed of light had been much higher in the dim cosmic past as a solution to various cosmological puzzles. Cosmologists did not rally to the idea, which even Dr. Magueijo admitted violated relativity. His co-author, Dr. Albrecht, himself called it an idea that is "not even properly born yet," and said it needed to find roots "in some convincing physics."
In the intervening years, as a sideline to his day job as a conventional cosmologist, he and a growing number of comrades have continued to tinker with modifying relativity in a variety of ways that go under the umbrella name of V.S.L., for variable speed of light theories.
In the science world, the book might attract attention for its jaunty and irreverent style as well as for its content. "What the hell, it's only Einstein going out of the window . .
Asked how he expected his colleagues to react to the book, he answered, "It wasn't written for them; it was written for the public." He called it "a very honest view of how scientists feel," adding, "It's the language I use normally."
The main motivation for considering V.S.L. theories, Dr. Magueijo explained, comes from the as-yet undiscovered quantum gravity. In relativity there is only one special number, the speed of light, but in quantum gravity, he explained, there is another special number, known as the Planck energy, equivalent to 1019 billion electron volts. According to quantum gravity thinking, an elementary particle accelerated to that energy will behave as if space and time themselves are lumpy and discontinuous and all the forces of nature are unified.
According to relativity, however, Dr. Magueijo explained, differently moving observers could disagree on how much energy the particle had and thus whether it was displaying quantum gravity effects or not. In short, they would disagree on what the laws of physics were.
"Perhaps relativity is too restrictive for what we need in quantum gravity," Dr. Magueijo said. "We need to drop a postulate, perhaps the constancy of the speed of light."
The most recent buzz in V.S.L. circles is about something called "doubly special relativity." In 2000, hoping to fix the cosmic ray problem, Dr. Amelino-Camelia proposed modifying the rules of relativity so that there would be a limit to the momentum that any particle could have, just as now there is a limit to the velocity.
Subsequently Dr. Magueijo and Dr. Smolin of the Perimeter Institute proposed their own doubly special version in which there is a limit to the amount of energy that an elementary particle can attain, namely the so-called Planck energy, at which the forces are unified and quantum gravity effects dominate.
One casualty of this tinkering, the V.S.L. scientists agree, will be everyone's favorite formula, E=mc2, to be replaced by a more complicated, cumbersome equation that Dr. Magueijo reproduces in his book.
A mark of all the doubly special theories, Dr. Magueijo said, is that the speed of light will vary with its color, with higher frequencies and energies going slightly faster than lower ones. That might manifest itself in observations of gamma ray bursters, distant gargantuan outbursts by an upcoming NASA satellite called Glast (gamma ray large area space telescope), scheduled for launching in 2006.
The theory also predicts that light should slow down near massive objects and actually come to a stop at the end of a black hole, preventing anything from entering that dark gate, Dr. Magueijo said in his book. In principle the effect, he said, could be tested by spectroscopic measurements of the light emitted from dense objects like neutron stars.
To some physicists, however, the very idea of variations in the speed of light in a vacuum -- the c in E=mc2 -- is meaningless. The miles and seconds by which speed is measured are human inventions, they point out, defined in fact in terms of lightwaves, so the whole notion of the speed of light varying is circular. In the last analysis, they point out, all physical measurements boil down to a few dimensionless constants like the fine structure constant, alpha. "What we measure objectively is whether alpha varies," said Dr. Michael Duff of the University of Michigan in an e-mail message.
Dr. Magueijo said those criticisms were technically correct but said the speed of light was one factor of several in the formula for alpha. So if alpha varied, as some astronomical measurements have suggested, one could choose to think of it as a variation in the speed of light, of electric charge, or even a variation in another number known as Planck's constant -- or all three -- if that made the math simpler. "It's a matter of convention," he said, adding, "you make the simplest choice."
Despite all the activity, scientists agree that they are mostly in the dark about the deeper consequences of these conjectures. "Some may eventually be developed to the point of being a credible alternative to relativity," conceded Dr. Kostelecky, saying that he suspected that others might not really change relativity or might have already been excluded by existing experiments. Without a systematic analysis it was impossible to know.
Dr. Amelino-Camelia said that the doubly special theories preserve Einstein's principle that all motion is relative, but at an unknown cost to the rest of physics."We paid a dramatic price for relativity: the notion of absolute time," he said. "This time it is not completely sure what is the axiomatic principle we have to give up."
Dr. Albrecht urged caution and said physicists needed guidance from experiments before tossing out beloved principles like relativity. "The most dignified way forward," he said, "is to be forced kicking and screaming to toss them out."
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NYT article
...and the beauty of special relativity.
They key thing is that the speed of light is fixed relative to *everything*. This means that if I'm standing by the highway and measure it, I get the same speed as a person in a car going 60 mph away from me. And since the speed of light is fixed, everything ELSE distorts to make up for it. That includes time (time dilation) and space (Lorentz contraction). It leads to some pretty freaky and amazing consequences.
E=mc^2 is actually a simplified form of the real equation, E=mc^2/sqrt(1-v^2/c^2). A convenient graphical depiction can be found in a few seconds with google, or here: http://www.btinternet.com/~j.doyle/SR/Emc2/Derive. htm.
186,000 Miles per Second. It's not just a good idea. IT'S THE LAW.
As for magnetism, that travels at the speed of light -- that has been known since Maxwell's time. Basically, that's what electromagnetic radiation is: a changing magnetic field causes a changing electric field, which causes a changing magnetic field, .... The paradox was that Maxwell's equations give you a constant for the speed of light, without reference to the velocity of the observer, so people assumed that they are valid only in the rest frame of a mythical "ether". Einstein showed that Maxwell's equations are correct for all observers, and it is Newton's/Galileo's ideas which are wrong.
Incidentally, just like electromagnetic radiation, GR implies that gravity waves should exist too.
He will still be a great physicist that helped bring us to where we're at in science today.
I dont see the big deal in "disproving" him. It's sad that people will take some sort of glee in thinking "Ha! Einstein was wrong!" Einstein himself would be glad to see people come closer in figuring out the natuer of the universe.
Given the knowledge and tools available to him at the time, its amazing he came up with something in 1904 that people nearly 100 years later are still trying to figure out how to improve or disprove. Today we have the advantage of knowing how to look at things the way he did.
Einstein's abilities, creativity, and ideas will have a permanent influence on humanity's acheivements.
c is relative to the observer, no matter which observer we're talking about. Anything that can measure the speed of a photon will always measure it going at the speed of light through that substance. Through a perfect vacuum, it's c. Through space it's c - epsilon (epsilon is an infintesimally small number). Through water it's about c/1.335.
If you are zooming past me at half the speed of light and both of us measure the speed of a particular photon at the same time, we'll both measure it's speed as c. What will be different about our two measurements is that you'll see a higher energy photon (bluer) than me if the photon is moving opposite to your motion relative to me and a lower energy photon (redder) if the photon is moving in the same direction as your motion relative to me.
No particular point in space is special. Once you identify where the observer is located, you can call that point in space an "origin" or "zero" and make all of your measurements from that point in space. The rest of the universe relative to that origin is called an "inertial reference frame", but it's just the same as any other reference frame. There's another trick. Behavior of things in inertial reference frames is time dependent because gravity pulls your frame around and changes everything around it slightly every moment. Besides that, two inertial reference frames may have a relative velocity but for a moment share the same point in space (the example above).
That's when tensor math starts to come in handy. Don't worry, I won't torture you with that.
Relativity, once you grok it, will bend your mind. From a metaphysical perspective, it emphasizes the reality that most of what we call facts are actually just high probability observations.
Remember, there is no spoon.
Regards,
Ross
The more we learn where our knowledge is incorrect the more *correct* it becomes. The job of the scientist is thus to question *everything.*
The very thing that shakes your faith in our knowledge is the very thing that *strengthens* our knowledge.
Think about it.
KFG
Comment removed based on user account deletion
A blackhole warps space and time around it. Light travels in a straight line, but since the space it is traveling over is warped, it enters the black hole.
The light itself does not speed up or slow down. From outside the blackhole, light is moving away from an observer at the speed of light. From inside the blackhole, light is moving towards you at the speed of light.
You have to remember that "speed" is a function of distance and time. Time is not constant, but from any frame of reference (you for instance) however, the "speed" of light is.
The world is neither black nor white nor good nor evil, only many shades of CowboyNeal.
The fact that light is in orbit has *no* effect on its speed. You're thinking of light as a Newtonian object getting "sucked into" the black hole. Light isn't "sucked in." The escape velocity of the black hole is simply higher than the speed of light and the light follows a ballistic trajectory. . . at * the speed of light.*
Light is not Newtonian. It dosn't "speed up" as it falls, or "slow down" as it rises. That's kind of the point. Try working some simple Lorentz Transformations to begin to get a feel for this.
KFG
I'll let someone else torture you with tensors :o)
i ty.htm
l es/LIGHTCONE/
:o)s /List s/relativity.html
Here are three (of many) links that I've found in the past that deal with relativity and provide varying degrees of rigor and completeness in the explanations.
How stuff works! Talking about special relativity:
http://www.howstuffworks.com/relativ
A pretty interesting and more rigorous explanation:
http://physics.syr.edu/courses/modu
And finally, a question and answer format explanation
http://www.sciencenet.org.uk/database/Physic
This should get you a good set of basic coverage about relativity.
Nunc Tutus Exitus Computarus.
Lordy... You don't ask much, do you?
The speed of light is constant in all possible frames of reference, according to Einstein. Basically what he's saying is that for any two objects at rest relative to each other (regardless of their motion to the rest of the universe, they appear not to be moving to *each other*), time and space behave in the same way. The beauty of his theory is that no one object can be said to be at universal rest to everything else -- there is no universal frame to measure against. Therefore, every frame of reference is valid and will behave the same way. This kills Ether theory dead, since Ether theory depends on a universal frame of reference. If it didn't have a universal frame of reference, then space and time would start behaving oddly within your *own* frame of reference depending on your motion. This is not the case - the light on Pluto behaves the same way as the light on Earth, even though the two are moving in different frames.
It's only when you introduce out-of-frame references (I'm standing still, the train is moving at 60mph away from me) that relativity kicks in and the laws start to behave weirdly.
Not inconsistantly, just weirdly. It's all in shifting your viewpoint.
The trick with light is to realize that although it travels at the same speed in every frame of reference, the *wavelength* is what changes between frame. This is what that whole red-shifting/Doppler effect is about. The speed of light is constant; the color, however, changes depnding on your frame of reference. If you shoot a blue light at me while we're both standing still relative to each other, it looks blue to me. If I run away *really fast*, it will still be blue to you, but it will appear red to me because the wavelength alters even though it still travels toward me at a constant rate. Ditto if *you* run away from me - the light is blue to you, but again, it appears red to me, even though it travels at the same speed.
Light does not behave in the Newtonian way - acceleration does not effect its speed, only its wavelength. That's where the question of why light is constant to everything, even moving objects, is answered.
Weird, huh?
For a far, far, better explanation (and a fantastic grounding on String Theory in terms for non-physicists) check out The Elegant Universe by Brian Greene. If I could, I'd give this book a Pulitzer every year until the day I died.
point at c/2 from opposite directions they both gain infinite mass!?
Nope. Drop all your newtonian physics assumptions out the window. Speed is relative as well, and doesn't add in such a straightforward fashion. An observer on one object will actually measure the velocity of the other as something less than c. (pardon me if I don't go look up the exact equations right now). That's where relativistic time dialation comes from- time has to slow down to make up for the non-additive properties of velocity.
By that same argument if I am traveling at c toward Earth, Earth gains infinite mass and the gravitational pull drags me toward it even faster!
Wrong again. You can't travel at c toward earth, so the question is meaningless. It takes infinite energy for a massive to reach that velocity, so it's impossible.
No offense, but this makes no sense. Either none of us understand it, or the emporor has no theory.
Quite a bit of offense taken, actually. You missed the third possibility, that *you personally* don't understand it, and that physicists do. Do you really think that points as obvious as yours would have been missed in all the years that Relativity has been under close scrutiny?
Oh, well. People who argue "I don't get it, therefore it's wrong" annoy me.
Not more than a few year's after developing his theories of general and special relativity, Einstein realized that they weren't perfect. The simple reason behind his realization was that the theories of relativity didn't make sense when applied on a quantum scale, and the theories of quantum physics didn't make sense when applies of a relative scale. Einstein refused to believe that the universe worked in such a way that there had to be two mutually exclusive theories to explain physics on the very small and the very large scale.
Of course, the rest of the world was busy experimenting with his theories of relativity, but after he published them he quickly lost interest in their progress. He spent the rest of his life searching for what he referred to as the "unified field theory," a single theory that could properly explain quantum physics and relativity at the same time.
I'm not a physicist by any stretch of the imagination, but theoretical science does interest me. Brian Greene's book, The Elegant Universe does a great job of explaining the background on this. It's worth a look.
-- Have you ever noticed that at trade shows, Microsoft is always the company that is handing out stress balls?
But why do you think that your brain is capable of understanding the basic forces of the universe?
Your brain evolved to keep you away from things that want to eat you, find things you want to eat, and basically preserve you until you could insure that you have spread your genes. Last time I checked, understanding the basic rules of reality wasn't needed to ensure that you live long enough to breed.
Hell, we'er just lucky that the same math that works on our scale also seems to work when we look at how the universe works.
Even now, logic has begun to fail us when we ask the deep questions. Consider this: What made this reality? Oh sure, I know the theories that suggest that this universe might have been created by another universe, and at this level, cause and effect goes out the window, leading to the possibility that this universe can create the ancestor of the universe that created it, but what allowed this gestalt to exist?
There's an Heinleinian phrase that occasionally gets said on slashdot: There ain't no such thing as a free lunch (TANSTAAFL). Too bad that its wrong, since the universe is the biggest example of a free lunch in action.
[ Don't feel so bad - my brain also seems hellbent to make me survive long enough to ensure my genes are passed on. Damn thing is that my body agrees with it and is planning to expire in half a century in order to free up resources for my future offspring. Its a comspiracy, I tell you... ]
Just my $.02
On one hand, the formulations of string theory are Very Hard (TM). I'm sure you think youv'e seen hard math, but there's hard math and there's string theory math. Classic standard model quantum mechanics and general relativity is hard math, nice hard partial differential equations to solve. String theory math makes this look easy though. It's so hard that nobody has yet even formulated the exact equations - everybody's working with approximations. So the predictions that people are making with string theory may not be completely accurate, as they aren't working from the real threory, just an approximation of it. Nice, eh?
On the other hand, most of the quantitative predictions that string theory does generate are mindboggling hard to test anyway, since in almost all respects string theory agrees with classic quantum mechanics (there's an oxymoron...) until you get to some pretty insane energies (think plank energy).
Fortunately, recently a few physicists have come up with some more subtle qualitative predictions that should prove feasible to test (for example, string theory predicts that cosmic microwave background radiation should be pixelated - the big bang didn't do antialiasing:).
Dude......C is relative to B. It's C++ and Java that's relative to C. Cobol is a different species altogether.....
Life is hard, and the world is cruel
Yes. One of the hypotheses of relativity is causality, that is, one event can possibly cause another only if the latter occurs at a later time than the former, and this must hold true for all possible observers whatever their frame of reference.
Now, as you know, the passing of time for an observer varies with his frame of reference (his speed, to put it simply). Hence, given two events, the interval of time from one to the other will not be the same for all observers. But if one is to cause another, it must always remain in its past; the sign of the time difference "t2-t1" must not change whatever the observer.
Unfortunately, my memories of relativity are too scarce to put this into equations, but if you could travel faster than light, you could, say, watch an asteroid smash into the Earth and warn your friend on the Centauri stock market to sell shares of all Terran businesses before anyone could "see" the flash of the impact.
And in a given frame of reference (maybe that of a traveler aboard a STL ship in-between), it would look as if you knew about it before it happened; stretching it further, it would be possible for the traveler (maybe through another FTL "jump") to warn Earth before the impact. Bye-bye causality.
If these situations are not to happen, information must not travel FTL.
First off, I'm not a creationist. Indeed, I find that whole debate to be entirely infernal, as both sides seem to me quite flawed in their own ways. That being said. .
Occam's Razor bugs me. As a deductive tool, it is a pretty good one; it works for the most part. What I find unsettling, however, is that it seems to have become, thanks to its presentation and treatment in popular media, understood and accepted by many as a de facto scientific law when it is not.
It is a rule of thumb, and only a rule of thumb. --It is only a rule of thumb, because it is not always right. Every time something unexpectedly complex turns out to be the reality behind a phenomenon which might otherwise have been explained through simple means, Occam's Razor is blunted.
Example:
When Alexandre Graham Bell first announced to the world that he had discovered a way to send a voice signal over a wire, the world erupted with both excitement and disbelief. One major newspaper even ran a story written by experts which attempted to debunk Bell's claim. They used diagrams demonstrating that sound waves sent down thin metal tubes of the diameter Bell was using for wires, could not possibly travel the kinds of distances he claimed. The experts were engineers well versed in the science and dynamics of sound as employed in the kinds of voice communication pipe systems once used large ocean going vessels. To the writers of the article, they were being entirely reasonable.
"Which is more likely?" they must have asked themselves, "That Bell has created some magical new invention to send sound along miles of very thin tubes? Or that he is lying?"
Occam's Razor is deeply rooted in how one perceives, how much information there is available to work with, and what has been previously accepted by culture as normal and/or outlandish.
-Now Bell was, of course, proven to be right. When words crackled out from crude speakers for all to hear, the enthusiastic debunkers, (and there is never any shortage of enthusiastic debunkers or respected, conservative media outlets to give them a voice and print their diagrams), had to quietly go mum and withdraw their objections. But that was in part due to large forces which wanted and allowed Bell to be proven right. If you don't advertise a fact or discovery, facts and discoveries can easily vanish. People have short memories. People have short lives. Without active perseverance, knowledge is a self-burying commodity until it becomes large enough to self-sustain, and even then, it is not so very difficult to forget important turns of history after only a few fickle generations have passed.
Science as a concept, is a pure, wonderful thing, but it does not know everything. Indeed, many institutions are not so pure as the science which they employ; it is well known that individuals with weak morals, and corrupt institution will suppress data, twist data and even make up data on a basis regular enough that the public pool of knowledge has been polluted to the point that the employment of Occam's Razor is by no means reliable in today's arena of public thought.
Just something to consider next time you feel the need to slam a new idea. Remember that Occam gave us a deductive tool, not an irrefutable law.
-Fantastic Lad
What makes you think there even was a beginning? Keep in mind that we have never actually seen the beginning of an event and the end; those boundaries are imposed by us. Reality is really a continuous cascade of effects which themselves become causes. How do we know there even is a beginning to the universe?
Higher Logics: where programming meets science.
Please don't forget your subscripts! As everyone learns in basic special relativity, total energy, which is kinetic + potential, is
where gamma = 1 / sqrt( 1-v^2/c^2 ) and m0 is the rest mass.At v = 0, gamma = 1 and E = m0 c^2, Einstein's famous formula for rest energy. Kinetic energy is given by KE = E - m0 c^2, or
To see any appreciable effect of velocity, consider the situation where you are going fast enough to double your effective mass (gamma = 2). Solving for velocity gives v = c sqrt(3/4) = 86.6% of the speed of light. Not gonna happen with current technology (outside of atom smashers).As v -> c, gamma -> infinity and this is Einstein's rationale for saying it's impossible to accelerate any matter up to the speed of light, since doing so would require an infinite amount of kinetic energy. On the other hand, the formula for photons is
where p is momentum, h is Planck's constant, lambda is wavelength, and c / lambda = nu is the frequency. Since photons are never at rest (remember the constant speed of light?), you won't see any m's make an appearance here. And just for the record, this last formula explains the photoelectric effect, which is what won Einstein his Nobel, not E = m c^2.This post expresses my opinion, not that of my employer. And yes, IAAL.