Slashdot Mirror
Einstein's Theory To Go Beta Testing
pinqkandi writes: "This article over at CNN looks into the relativity of Einstein's theory of relativity (pun intended) as equipment becomes more and more precise. Soon atomic clocks will be placed in the International Space Station to analyze the accuracy of Einstein's theories. One of the lead researchers says that if Einstein's theory is not right, it will only need minor adjustments to account for changes in space-time, due to its deadly accurate precision."
time is a dimension like any other easily identifiable dimension. we exist in length, width, height, and across time. not to mention the fact that the perception of existance is, to most people, just has good as actual existance, but what makes time any less valid than length, width and height?
sig.
If you don't understand either one, take a look
here:
Hasn't this been proved already? What's wrong with those older proofs? Like the atomic clock in the airplane and GPS satellites?
Deadly precision? What has space-time done to you lately?
Karma: Good (despite my invention of the Karma: sig)
If you can think of an oak tree which lives several hundred years, the analogy can be made as well. I do not deny the fact that we can measure "time" or the passage of such, just that in a cosmic sense, time does not exist.
--- I'll have a Bloody Mary, a Steak Sandwich and a uh Steak Sandwich.
I remember in the seventies they got two atomic clocks and stuck one on a plane and after two years of the plane flying around aimlessly they found a minute difference
in time.
The joke of it all is that after a year some journalist asked why they didn't just stick it on a regular commercial jet but they didn't think of it at the time.
Mouse powered Chips, Open source Processors and Lego
While we might think that we are equipped to carry out the beta test on Einstein's theory, methinks we may not yet be ready.
Practically, what we understand from the Theory of Relativity is what we BELIEVE we understand, and that will influence what type of outcome we are searching for.
Plus, the equipments that we think are ready may not be ready.
Take the Atomic Clocks for instant
After all, the "ticks" of the atomic clock, no matter which type of "atoms" we base it on, still depends on the variable TIME - as "ticks per second".
Muchas Gracias, Señor Edward Snowden !
is here, with a little more information on Lorentz and CPT violation.
As a born pedant, when asked the question "What's the time?"
:D
My typical response is:
"An abstract system that allows one to distinguish sequences of events"
I then laugh till I puke
If nature abhors a vacuum, why isn't there more dust in the world?
Maybe it's just the way the guy was quoted in the article, but if they need to test in a "zero gravity" environment, how would the ISS be applicable?
I'd consider it a "weightless" environment, but not "zero gravity".
- Tony
AFAIK the current GPS satelite system makek adjustments for relativity in the signals it is sending around and they have been adjusting for this for years. See the articles at Metaresearch and lsu.edu for more info.
Soon accurate telescopes will be installed to make extremely careful measurements of Mercury's orbit to analyze the accuracy of Newton's theories. One of the lead researchers says that if Newton's theory is not right, it will only need minor adjustments, due to its deadly accurate precision.
Real Daleks don't climb stairs - they level the building.
Even as a joke this makes no sense. Relativity was alpha tested in the 1913 (IIRC) eclipse and has been tested very very thoroughly since then. This is just another fine-grained test.
Like, they put one of those into an airplane and flew it half around the globe or something.. That might have been another aspect of the theory though.
But one thing is for sure: They won't 'prove' Einstein in any way by doing this - but they might *prove* him wrong. Only negative proof can be done by example.
Love over Gold.
Too bad Einstein isn't around anymore...
He would have made for one heck of a great match on Fox Celebrity Boxing 3 with Stephen Hawking.
------
Today's Top Deals
Can a clock really be DEADLY accurate? A rifle, a smart bomb, maybe even a rolling pin weilded by an angry wife when her husband comes in late.... THESE can be deadly accurate... I don't think a clock can be.
Prevent linux based DDOS's!
http://linux.denialofservice.org/
The CNN article is not very clear as to what it says. This comes from the fact that There are two different theorys of relativity.
1 The special theory
2 the General theory.
The special theory concerns what happens to the laws of physics as a person is traveling at a constant velocity, whereas the general theory is concerned with bodys that are accelerating ( In general relativity acceleration and gravity are equivalent).
So since the ISS is in orbit it experences an outwards accerleration( the same as one experences as one goes round a corner fast in a car.) In space there is gravity on the ISS but it is very little. This means that the ISS will experence a slight change in the ticking rate that is recorded. But this is explained by the general theory of relativity and not the special theory.
"If variations in the ticking rate were discovered, Kostelecky says, it would be a "striking signal" that the laws of nature may be based on fundamental theories other than Special Relativity -- or perhaps in addition to it."
I thought this was precisely what special relativity does predict, that a moving observer experiences less passage of time than a stationary one, increasingly so as the speed becomes a significant fraction of the speed of light. If the ticking rate does not vary, then special relativity would be invalidated.
-- Adam
So, if I were to stop perceiving time, does it cease to exist? Things happen while you're sleeping, you know.
Probably this won't be so much beta-testing relativity as it is verifying the anti-relativists.
Karma: Bored. (Thinking about resurrecting the "Anyone else is an imposter" joke.)
No, you're still talking about perception. Time exists in a cosmic sense. It has nothing to do with the age of things that experience time; it exists as a dimension in exactly the way that the three spatial dimensions exist.
Saying what you've said is exactly the same as saying "we can measure the "size" of something, but size does not exist in a cosmic sense, it's merely our perception of how big things are".
This just in, from a 1903 Einstein press release:
One of Einstein's lead researchers says that if Newton's theory is not right, it will only need minor adjustments to account for changes in space and possibly time, due to our upcoming theory's deadly accurate precision.
Not that Salon is a peer-reviewed journal or anything, but this will give a little background for those who'd like it. http://www.salon.com/people/feature/2000/07/06/ein stein/
Karma: Bored. (Thinking about resurrecting the "Anyone else is an imposter" joke.)
NOW! Brand new on the Market: MS Relativitiy (future patches coming soon!)
gah, it turns out it was only slightly related... like a third cousin.
(smack me, i know it's an obvious joke)
I can't believe it's not lard!
This is an honest question. Most theories I know of have things they cannot account for, but I have not heard where relativity fails.
What is wrong with using existing equipment, like that hive of atomic clocks in the GPS system? They already transmit their time to just anybody that wants to receive it and all of the adjustments for relativity, etc., are known and can be removed for "raw" time measurement.
I guess the hammer and feather experiment just gets more expensive in proportion to the expansion of the beurocracy.
Eve Fairbanks says I drive a hybrid!LOL
Atomic clocks on ISS are a trivial test of relativity compared to Gravity Probe B, hopefully to be launched soon after DECADES of development. A one-pager "GPB for Dummies" is here. GPB tests not for alterations in time but another phenomenon known as "frame dragging" which has never been directly measured. There's been lots of criticism about GPB as being too ambitious, so there's been lots of independent reviews.
These tests might be more interesting on a craft traveling deeper into space. Maybe the next Mars mission? You might see greater inconsistancies.
Can I bum a sig?
Either this is a totally narcistic sense of time, or else this requies certain metaconditions, such as an immortal soul (or similar) with the ability to be unconscious. There could be the ability to connect/disconnect from various time streams, etc. But this goes into discussions that many folks find uncomfortable. And most such subject definitions of time do not try to integrate these other factors.
[shrug]
"It is a greater offense to steal men's labor, than their clothes"
An article (membership requires) in May Physics Today details the extensive corrections GPS must make for both special relativity (velocity corrections) and general relativity (gravity corrections). This has tested Einstein every day of the past 20 years, and he has held up.
So there planing to space-time using radioactive decay by increasing the potentinal of the decaying isotopes. hmmm.... prohaps they should try other 'artifacts'
All that will prove is that radioactive decay is relitive to the kenetic potential.
thank God the internet isn't a human right.
I heard GPS sattelites use atomic clocks to keep in synch with earth. They use the Theory of Relativity to adjust their times so that they stay in synch with earth because they move at a different speeds and in a different field of gravity.
Outdoor digital photography, mostly in New Engl
A play on words, sometimes on different senses of the same word and sometimes on the similar sense or sound of different words and they need a hefty bit of setting up, like a large story resulting in the punch line "I don't know for whom the Tell's bowl"
--fetch daddy's blue fright wig, i must be handsome when i release my rage
Whoaahh.. Okay we are now moving from the realm of science, physics and technology into existentialism. Which at some fundamental low-level must co-exist. I wonder how low-level we can get? Maybe one day we will be able to see the source (code) of the universe... Though maybe it isnt the stepwised, serialized kind of thing we imagine- but at the end of the day some super-massively, multidimensional parallel process occuring in multiple dimensions sychronously in a truly chaotic access pattern. The fact we experience the universe at all prooves that it exists- however flimsy the existence- it exists. To put it another way - does a "virtual" world really exist? Yes and No- no because its existence may seem "meaningless" in the "real" world, yes because whatever it is- *it is*. Superstrings- the universe performing high-level multithreading? Time is as real as the chair your sat on- wether you beleive in its existance or if it is an illusion. An illusion is still *something*. "I think therefore I am". If the universe is just an individuals thoughts- it is still something. After all- in what medium are these thoughts... Its all relative.
OrionRobots.co.uk - Robots From sol
Time doesn't exist, depending on how you look at the situation. I don't know that your interpretation has been proven, though it has some merit. Isn't time technically a fourth dimension, t ? The question should really be, is "time" a by-product of movement in space, or is movement in space possible because time already exists?
Some said that if things exists, that's only because we're here to look at them...
Maybe one day we will be able to see the source (code) of the universe...
Yeah! Hey, God, show us your code so we will be able to debug it!
8-)
I wonder if Scientists ever play practical jokes on each other and sneak into the lab to make the Atomic Clock blink 12:00
http://www.kubuntu.org/
Of course it ceases to exist. I mean, when trees fall in the woods and no one is around, you know they don't make any noise, right?
Time most assuredly does exist. I am perceiving time, therefore I am perceiving something. Whatever this something is, I define as "time". Viola.
You may think you can wiggle out of this by claiming that what I'm perceiving is an illusion, but no such luck; I define your claimed illusion as "time" (without conceding your illusion point.) It doesn't matter how you try to do this, I can always go one meta-level higher. You can't win without throwing out logic, at which point I declare moral victory anyhow.
The parent is really a hidden instance of "overgeneralization".
- "I know of this thing 'x'", where "x" is "time" today (no pun intended).
- "This thing 'x' does not exist."
- "Therefore, no thing thought of under the word 'x' exists."
I hope I don't need to spell out why that's fallacious logic? (Hint: Just because you don't understand something doesn't affect the universe. Hint 2: You can't go "Newtonian gravity is incorrect. Therefore, there is no such thing as gravity." It's the same form, honest.)Of course the universe cannot be totally explained and there's a lot of mystery out there. Indeed, that's exactly why making up fake mystery is a waste of time! There's plenty to exercise your sense of wonder on or whatever other reason your subconcious is rebelling at this message for; why make up fake stuff like this? You need all the help you can get; throwing out logic pretty much leaves you adrift, with no clue. You wanna be that way, fine, no skin off my nose, but don't suffer under the illusion that you're any more 'enlightened' then me.
That time may or may not be a derived quantity is irrelevant; I am no less sunburned even as I write for "electromagnetic radiation" being properly a derived thing from the nature of the universe. Derived things exist! A triangle is still real for being made up of three line segments. The angles of the triangle are still real too, despite needing two lines to exist.
First, you simply cannot see it as its velocity aproaches c because it is going too fast, you sux0r. Thats "...be cause..." c is the speed of light, this is much faster than your mom's minivan can go (just to give you an example you would understand). Secondly, you sux0r. And finally, it will shrink such a small amount (about the size of your...) you would never really be able to notice it.
Space-time is a dimension in the theory of Einstein. But, if time is an dimension, we can travel in it in all direction like we can do in other dimension. Right now, time seen to be an one-way dimension. In all the others dimensions, we are always between two horizon of this dimension and we can travel in the direction of the horizon. Time doesn't permit this, so I think that the Einstein analogy doesn't stan the analysis.
Ceci n'est pas une Signature !
I see!
Hope, that you are not too tired now.
- Thomas
Remember, none of this has totaly been proven. Although some of these theories work most of the time, none of them really work all of the time. Plus, no one really looks at other theories. One that is becoming more and more recognized is the Holographic model or Holographic theory, check it out, it makes more sense and works almost 100% (if not 100%) of the time. Read Holographic Universe.
That's my bet.
Be cause I can't see, what happens with a circular train around the Earth. How does it shrink, when it's velocity approaches c?
Oh, Einstein was wrong because you can't see?
Special relativity concerns only objects in uniform straight-line motion. A circular train around the Earth is not straight-line motion, so general relativity comes into play.
On a small scale, an observer would see the effects of special relativity on the train cars nearby (shrunken in the direction of motion, clocks appear slow) but on the scale of the earth, these effects would be offset by general relativistic effects.
Hey kids, there's only 5 days left 'til Yak Shaving Day!
I think it's important to realize the possibility that time could be a fractional spatial dimension. This would explain our lack of degree of freedom and for a bonus it would also explain the patterns we see in nature as overflowing information into integral 3-space. Fractals are fun too.
-metric
It only depends on the definition of the noise.
If the noise is that thing that comes to your ears and hurt your brain, there won't be any noise when nobody's there.
But if the noise is the air vibration at certain frequencies, then there will be a big noise!
Maybe you can ask to the owls that lived on the tree!
As I recall, it was proven wrong by the detection and acknowledged existence of Tachyon particles travelling at over the speed of light when detected...
References? I somehow missed the scientific article on the detection of tachyons.
If you really want to test the theory, build an ion engined probe with small nuclear battery and atomic clock, transmitters, etc... and enough fule to acclerate to relativistic speeds.
Oh, I'd love to, but I have to mow the lawn tomorrow, maybe I'll get to it next week. Um, don't you think if we could do that, we'd find something better to do with it than test relativity... say, fly to Mars?
The theory has to be wrong because we have observed multiple instances of the violation of conservation of energy and the hard and fast rules around C speeds.
And I assume you have some references here as well?
Hey kids, there's only 5 days left 'til Yak Shaving Day!
> Special relativity concerns only objects in uniform straight-line motion. A circular train around the Earth is not straight-line motion, so general relativity comes into play.
Is that so? Okay, where's the straight line in this Universe.
Will this measuring satellite go by the straight-line? By my best knowledge, those orbits are all elliptic.
- Thomas
They already have quite accurate measurements on the effect of relativity on reference frames moving at different speeds and at different potentials in a gravity well. They are dead on, so far. For example, the GPS system (which uses atomic clocks generating signals to locate where you are) needs to have its clocks reset periodically because they get out of sync with ground clocks. I'm sure there is more than enough literature on this part of the theory for anyone to be happy. The only place where i would begin to question it is when you are dealing with an extreme difference in gravity (not on the velocity side, that has already been tested). I suppose (since it is a MODEL after all, just an extremely good one) that when gravity is very large other terms might begin to show themselves, if they do exist.
That example fails with Special Relativity since the train is accelerating (moving in a circle). However, I don't know how it behaves under General Relativity. Note that when you are on the train, it is still the same length. Length contraction only applies for an observer moving at a different velocity to the train. -s
ݼ)s$æúßðíÊ'öX'îò5^àûßQç£
Tachyons are hypothesized to travel faster than the speed of light. It's a common misconception that Einstein's theories prohibit FTL travel - they do not. They do prohibit massive particles from accelerating past the speed of light (would require infinite energy). Massless particles like photons and the theoretical tachyon don't have this problem.
I thought Tachyons were a prediction, not experimentally verified? You are right that there are a few inconsistencies with GR though, mainly with Quantum Physics. -s
ݼ)s$æúßðíÊ'öX'îò5^àûßQç£
It's obvious that E = mc^2 + 1.479
--Steven
Time does not exist
Than what separates actions from one another? Beside that, there is a rules that no two items can be in the same place at the same time. If time didn't exist, than two things would either, be allowed to be in the same place (our perception just doesn't see it), or no two things can ever be in the same place. This latter part can further be extrapolated to say that no two things have the *ability* to be in the same place, ever. I believe both of these to be untrue, so time must exist.
Have you read my journal today?
So, if I were to stop perceiving time, does it cease to exist?
Absolutely not. Although you stop realizing that you're perceiving time when you're unconscious, you really don't stop perceiving it. If you go to bed at 2am and wake up at 7, most people don't still think that it's 2am, as their body has perceived the flow of time in its dormant state.
If it wasn't for our biological clocks counting time, how could bears hibernate at eactly the same time every year? How could birds begin their migratory journeys every year?
If I'm not mistaken time is calculated in our bodies by the observation of changes in the electromagnetic and gravitational fields around us. I think it has something to do with the inner ear or something, the same part that helps us keep our balance, but IANAneurologist...
whereas the general theory is concerned with bodys that are accelerating ( In general relativity acceleration and gravity are equivalent).
Common misconception. Acceleration and gravity are not equivalent in General Relativity. They are *locally* (that word is extremely significant here) indistinguishable. The fact of the matter is that Special Relativity can handle acceleration just fine by using calculus. General Relativity is only needed where spacetime is not flat (i.e. in the presence of gravity), since the two postulates of Special Relativity only hold in regions of flat spacetime.
A detail that I left out of my previous post is that Kostelecky and co-workers have developed a framework describing a very general set of extensions to the standard model which violate Lorentz invariance. You can find out more about this set of extensions at his website and in the papers referenced there. His framework (which I don't understand in the detail which I should) includes a set of parameters (whose values must be determined by experiment) which are Lorentz invariant in some underlying high energy theory but lead to CPT and Lorentz violations in the low energy limit (where the low energy limit includes everything from atomic clocks to the highest energy accelerators).
It turns out, however, that a standard atomic clock such as those used in the GPS satellites is not sensitive to these effects. In the measurements Kostelecky is talking about and the measurements we have done on the ground, one looks not at the standard clock frequency (based on the hyperfine transition) but instead at an auxillary frequency (a Zeeman transition) which has a first order magnetic field dependence. This frequency is sensitive (in leading order at low magnetic fields ) to the effects Kostelecky's framework predicts.
Therefore, one needs to operate an atomic clock in a slightly unusual way to search for these effects. In the hydrogen maser measurements we have performed (the Phys. Rev. D paper I mentioned) we measure the standard clock frequency while "tickling" the Zeeman frequency and record the shifts. A similar technique is being proposed in space. I wouldn't think that such a technique would be realistic on the functioning GPS satellites.
they got two atomic clocks and stuck one on a plane and after two years of the plane flying around aimlessly they found a minute difference
I've heard of this experiment, but I have a serious question about it that's always bothered me.
This assumes that Clock A is stationary at 0 mph and Clock B is traveling at 400 mph, right? But, given that the Earth rotates AND orbits the Sun that assumption isn't really true. Relative to a given point, sometimes they're going faster and other times slower. Also, since Clock B is ideally flying in a big circle (around the Earth) doesn't its velocity (in relation to a set point) average out to 0 as well?
I would think that this experiment would only work if Clock A was dropped off somewhere in space and Clock B was launched in a straight line relative to Clock A. Where am I wrong?
but what makes time any less valid than length, width and height?
I don't think Einstein ever said that time was any less valid than length, width, and height. All are relative, according to Einstein's theory.
"Time doesn't exist" is an inaccurate representation of what Einstein said. Of course time exists, because we define it to exist.
No two fermions... Bosons can occupy the same energy state at the same "time"...
Assuming you believe bosons exist. And even then, fermions definitely exist, thus not changing anything said.
Have you read my journal today?
My mom always said, "Jim, you're 1 in a million." Given the current population, there are 7000 of me. God help us all!
I wonder if Scientists ever play practical jokes on each other and sneak into the lab to make the Atomic Clock blink 12:00
I just got a flash of Professor Frink walking into the lab, "Oh, for crying out glavin..."
As coauthor of the Lorentz-violation paper being discussed, I'd like to reply to a few comments that have been made. This comment seems like a good starting point.
_Special_ relativity and quantum mechanics have no trouble getting along. In fact, the so-called Standard Model of particle physics, based on relativistic quantum physics, is an enormously successful theory. The trouble lies in getting relativistic gravity (i.e., _general_ relativity) to play nice with quantum mechanics. This is where string theory comes in.
The good thing about string theory is that it allows gravity and quantum mechanics to get along. The bad thing about string theory is that there is absolutely _no_ experimental evidence for it, and there are almost no possible tests of it that could be conducted in the near future. Lorentz violation is a major exception:
The afore-mentioned Standard Model obeys a certain symmetry called ``Lorentz symmetry'', which lies at the heart of special relativity. However, string theory allows Lorentz symmetry to be broken. Thus, any experimental detection of Lorentz violation could be a great signature of string theory, and, maybe, quantum gravity. Moreover, there exist current experiments that are capable of detecting Lorentz violation to a very high precision.
To summarize: We are studying Lorentz violation because (1) It is a possible signature of quantum gravity, and (2) It can presently be studied to very high precision.
Chuck
But I do believe in uncertainty.
Does this mean my GPS will stop working now?
:)
There are actually two different effects that can cause one observer's time to move faster than anothers:
1) From special relativity, if the observers are moving relative to each other, _each_ will see the other's clock as moving slower than theirs. This causes the twin paradox, which ends up being resolved by...
2) From general relativity, if an observer is "accelerating", their clock moves slower relative to a non-accelerating observer. Note that in GR, staying stationary in a gravitational field is actually "accelerating": You can't distinguish between sitting in an elevator that is in free-fall and an elevator that is floating in space, or between an elevator that is sitting still in the earth's gravity and one that is accelerating upward while in space.
The effect that causes the atomic clocks to show different times is the latter: one plane is 30K feet higher than the other, so assuming that it doesn't do a lot of stopping and starting or high-G turning, its average acceleration is less.
So for all two-dimensional beings (prove there aren't any), they can be safely assured that there is no third dimension? This is absolutely silly. Just because we happen to be progressing in a usual manner in a fourth dimensional "space", instead of being able to progress at will through it, does not make said fourth-dimensional space nonexistant. However, everything we know of in this universe (a theoretically infinite set of three-dimensional spaces positioned in a fourth-dimensional space) seem to behave as we do (traveling in what we see as a linear path through the space).
Think of it as a line (1D) moving slowly across a square (2D). We are just part of a "box" (3D) moving slowly across(?) time (4D). The memory is not simply the memory of humans of this sequence, but the memory of large particles in the universe of this sequence. All atomic and greater behavior is governed by its progression across time. Time, for we quasi-4D beings is not 'perception and nothing more' any more than space, for a 2D/quasi-3D being is merely 'perception.' It is simply a dimension which exists outside of our ability to control and navigate.
Incidentally, conceive of a 5D space containing an infinite number of 4D spaces. Neat, huh?
"question = (to) ? be : !be;" --Shakespeare
Remember, none of this has totaly been proven.
But remember, nothing is even totally proven in science. The best we ever have is a theory that hasn't been proven wrong yet.
Just because *you* don't understand how it all fits together, doesn't mean it doesn't. The rules do work "all the time" - if they didn't, physicists wouldn't find them very useful. The rules of special relativity apply everywhere, all the time, but they only produce the unusual time/mass dilation effects in situations involving relative differences in velocity. Ditto for general relativity: as far as we know, it applies throughout the universe at all times; however, since it's based on the strength of the gravitational field at any point, its effects vary. If these rules *didn't* vary in their effects depending on the situation, it would either mean they were wrong, or the universe would be an incredibly static place.
This is because they came up with an idea, found an area that it didn't work in and had to invent rules that worked for that area
This is completely wrong. When this has happened, it typically results in an improved theory which completely explains all areas in question with a single theory. Try reading Thomas Kuhn's "The Structure of Scientific Revolutions" for more on this.
As for your tangential link to terrorism, it's hard to see how ignorance is going to help to achieve international peace.
Agree!, time does not exist. Time is there because things change, everything in this universe changes. The earth rotates, the trees grow, we got older not that because there is something called "time" that created all these events but it's because of these changes we preceived and though of something called "time" to keep track of a series of events.
The GPS satellites are not geosynchonous. They actual hurl through the sky at a qhick pace. When they built the satellites, they built the atomic clocks in each one to the wrong time base. They actually didn't read correctly on earth.
Once in space, if you were sitting on the sattelite, the time would still be wrong. However, the earth perceives the satellite atomic clock as working fine once it's in motion relative to earth. No, this isn't the doppler effect. It's empirical proof of relativity. It's also one of the coolest things I have read about. I am amazed they didn't make a bigger deal of it.
Why can't they do the same experiment using a space telescope and a pulsar?
If a story appears ONLY on CNN, then you should be wary. However, most significant scientific stories are mentioned on CNN sooner or later, so you shouldn't use CNN as your sole criterion for the value of a story.
Chuck
There are a lot of GR corrections that one must make to GPS to get decent accuracy out of it. In fact, there is a bit of a scandal because none of the GPS receiver makers have made public their correction formulae (standard "if we publish then we'll just be helping our competitors" philosophy).
There was a good article in the May edition of Physics Today about relativistic corrections to GPS, unfortunately the web version isn't free. If you're near a university, they should have copies of PT in their physics library.
Actually, GPS knows about this and takes advantage of it. It is the only consumer relativity application I know of.
The GPS SV's are going about 3900 m/s which is a sufficient percentage of the speed of light for relativity to come into play. If relativity weren't taken into account and Einstein obeyed, you'd be off by ~100 meters.
The correction could be done in the receiver or the signal could be biased in the SV. Following the Principle of Alice's Restaurant:
Factoring this correction into the SV, the onboard clocks use a frequency of 10.22999999543 MHz and your GPS receiver uses 10.23 MHz. This simplifies the GPS receiver software immensely.
GPS was designed during the 1970's by some really smart forward thinking guys.
The CNN article is one of the worst examples of science writing I've *ever* seen. I even thought of submitting it for that purpose alone. Now, what does it mean that Slashdot took it seriously? Good lord.
> Just because *you* don't understand how it all fits together, doesn't mean it doesn't.
...
But if nobody can show me how they do fit
> The rules do work "all the time" - if they didn't, physicists wouldn't find them very useful
In the case of the circular train - how do they work? I am asking.
> The rules of special relativity apply everywhere, all the time
Yea, yea - HOW do they work for my example?
>, but they only produce the unusual time/mass dilation effects in situations involving relative differences in velocity.
I am standing by this train. What do I see?
> improved theory which completely explains all areas in question with a single theory.
Excuse me! How it works for the circular train?
> Try reading Thomas Kuhn's "The Structure of Scientific Revolutions" for more on this.
I see no answer to my question there - either.
- Thomas
No, the passing of time is defined as the increase of entropy. You are making things up.
Did you know you can fertilize your lawn with used motor oil?
Look it up, do a google search or something. Do your own homework, before posting something you obviously know little about.
-- Waht? Tehr's a preveiw buottn?
Is the time you are referring to, a notion of "its 11 O' clock" or are you referring to the actual abstract notion of time ?
:). If you want to dispute the parameter "time" in the second law and quantum axioms - well that notion _as of today_ is robust.
The abstract notion of time, as of today, does exist. Crudely speaking it is defined as "an instant x is "older" in a scale than an instant y if the entropy of the universe corresponding to x is greater than the entropy of universe corresponding to y" This definition is based on the second law of thermodynamics and is accepted to be the only true notion of abstract time. And the second law has stood the test of time (no pun intended). Now this gives rise to the question if the second law is "correct". Well we dont know. We havent observed violations. So as of today time exists.
And of course there is quantum theory. Whose basic axiom says "Action" pervades the universe and is quantized. (Action is actually energy x time and it is distributed in chunks proportional to planck's constant). Have we observed a violation to the "quantization axiom" itself so far ? Well no. Is the therory successful ? Well yes. It has predicted things that have been checked out due to experimentation. So as of today time exists.
Moral of the story: Time is just not an illusion that physics guys are toying with. It is an actual parameter, an experimentally measurable quantity, which is well characterized and is a vital part of some basic theroies (that till today) characterize the universe pretty well. If you choose to define time as "20 mins have passed when I have the urge to pee after a beer" that notion is debatable
-Dracken
It doesn't really matter until you meet the other person again anyway.
... but once you're both in the same reference frame again things will have settled out so that you agree on the "direction" of the discrepancy.
The acceleration along the path you each take determines who, if anyone, is ahead.
If your trips were mirror images of each other, then on the outgoing journey (accelerating away) you'd each see the other's clock slow down.
On the way back (accelerating towards one another), you'd each see the other's clocks speed up again until they were back in synch when you met.
If the trips were not completely symmetric, then there will be a discrepancy
DNA just wants to be free...
Fact: Scientists are mammals
DNA just wants to be free...
I choose to follow the logical progression that is 1D->2D->3D->4D... The human perception of "rate of change" and how we handle the understanding and rectifying of our quasi-4d selves is purely a mortal problem. Obviously, relativity comes up when trying to observe a higher dimension from what is effectively a lower one. This is my personal understanding, and a lot of it is horribly basic and simple, but I think what science will (eventually) end up doing is describing something that works quite a lot like this.
"question = (to) ? be : !be;" --Shakespeare
Einstein's skeleton v. Hawking w/o wheelchair? Now that's tasteless entertainment.
It's a common misconception that Einstein's theories prohibit FTL travel - they do not.
Technically, no they don't. Practically, they might, because the transformation of time/space coordinates screws up causality. For example, we send a spaceship from Earth to Neptune faster than light. It leaves Earth at 1:00pm and arrives at Neptune at 1:06pm (Central Daylight Time, before you complain about time zones - we're launching from my backyard). In the frame of reference of an alien spacecraft moving past Earth at a high sublight speed, 1:06pm at Neptune occurs earlier than 1:00pm at Earth. This is because of the transformation of space-time coordinates. If the aliens have to wait for light from Neptune to get to them to see it, we're OK, but if they have some kind of subspace sensors that can see the event as it happens (in their reference frame), they can prevent the launch after they've seen the arrival at Neptune. Oops.
A good space-time diagram is worth a thousand words, so look here for more. The example he uses is different, but the idea is the same.
His site also has an explanation of how FTL might work without these paradoxes. It hypothesizes a special reference frame (subspace, of course) for objects traveling faster than light. This reference frame would match that of nearby massive objects (planets, stars, etc). In this model, the information that our ship had arrived at Neptune could not go backward in time relative to our solar system, so the aliens could not know the ship arrived at Neptune in time to stop it.
Incidentally, this means that a ship moving at sublight speed through a solar system would be able to use its subspace sensors to see things that have just happened in our reference frame, but are actually in the future in theirs. But, they can't do anything with the information to prevent the event before it happens.
Unfortunately, we have no way to verify any of this sort of speculation, and probably won't for the foreseeable future. It's clear that if relativity as we understand it is correct, then FTL travel can violate causality. Whether this means it's impossible, no one knows.
Hey kids, there's only 5 days left 'til Yak Shaving Day!
Correct (kinda), but if percieve it - it exists. Is the perception of any other higher dimensional being that doesn't percieve time more correct than ours? No, its just a different perception where everything is relative except for one thing...
Volunteer Mozilla developer, RPI Student.
In fact the opposite is the case. No one has any reason to believe that general relativity is in error, but as part of good science it is being tested anyway. One can never prove a theory; one can only disprove it. So the best you can do is test your theories with greater and greater precision as the opportunities present themselves.
It's a case where this is, in effect, a pretty mundane story (a very well-established theory is being routinely tested), but the journalist in question is implying that there is some doubt as to its validity. Of course, it's possible the experiment will reveal deviations from general relativity's predictions, which would indeed involve "minor corrections" to the theory since it is so accurate in other areas, but there is a definite spin being put on the story which isn't in the underlying facts.
Special Relativity, concerning things moving uniformly fast relative to one another, can be shown to be a special case of General Relativity, concerning things accelerating, or in a gravitational field, or rotating.
Unfortunately, while the effects of Special Relativity can be deduced in relatively (heh) simple algebra, the effects of General Relativity require very complex math, which is why you're not going to get a good answer on Slashdot. There might be folks here that can figure it out, but they probably won't get back to you for a while.
Best guess is that, if you're standing next to a hypothetical train going around the Earth at half the speed of light, you'll mostly just see Special Relativity effects - clocks on the train appear slow to you, the cars look short, and the mass of the cars is increased. Observers on the train (assuming the centrifugal force* doesn't turn them into chunky salsa) would see your watch running slow, and you would appear shortened, as would the tracks around the Earth.
The catch is, the circular motion around the Earth creates a pseudo-gravitational field** inside the train that has its own set of effects, and calulating how they are perceived by an outside observer is more difficult.
I think your earlier confusion was that if the train cars shrink as seen by an outside oberver, how does the train stay attached? The best answer that can be given in a few minutes on slashdot is that the General Relativity effects balance it out somehow. This is the same answer that has to be given for the Twins Paradox, except that that one isn't too difficult to explain since there's no rotation involved.
* - yes, I know centrifugal force doesn't really exist, but is an observational by-product of inertia.
** - the pseudo-gravitational field is the same as the acceleration caused by the centrifugal force that doesn't really exist.
Hey kids, there's only 5 days left 'til Yak Shaving Day!
If you think if the fact that you have a bunch of differnt rules, some apply here, some apply there, nothing really works all of the time.
Actually, General Relativity works all the time*. It's just that in the case of uniform motion, it's easier to use Special Relativity (which is just a subset of General). And, at low speeds, Newtonian mechanics is much easier than even Special Relativity.
And its great to wonder and explore, but maybe we should focus more on other problems?
I hardly think the relatively (heh, heh) tiny amount of time, money, and thought put into this experiment would make a dent in any of the world's "real" problems. Besides, what are the scientists going to do, release a paper on how people should be decent to each other? That's been done before on several occasions by non-scientists, and the results have been arguably less than satisfactory. One of those "papers" has been used to justify 9/11, another was used to justify the Spanish Inquisition**.
* - except on very small scales where Quantum Mechanics gets invovled. Maybe someday this will read "String Theory (or the like) works everywhere, it's just that it's easier to use Relativity on big stuff and Quantum on small stuff and only use String to figure out singularities"
** - yes, I know the motivations behind these acts aren't entirely (or perhaps at all) religious. The point is that the books don't work to make their readers decent to each other.
Hey kids, there's only 5 days left 'til Yak Shaving Day!
I've found this explanation which seems reasonable and short, but GR is used to explain it.
Hey kids, there's only 5 days left 'til Yak Shaving Day!
Well, there was a good point there - every theory except the ones we have now has been proven wrong at some point. There's not really any reason to believe that the theories we have now should be different. Judging from past results, it is probably true that we will find problems with relativity at some point.
Hey kids, there's only 5 days left 'til Yak Shaving Day!
In the case of the circular train - how do they work? I am asking.
...
Excuse me! How it works for the circular train?
I was replying to an AC with a strange view of the applicability of physical theories. ShavenYak has already given a reasonable answer to your train question.
To understand what happens with the circular train, I'd suggest first trying to understand how simple special relativity really is - the Lorentz transformations which form the basis of special relativity involve little more than a simple application of geometry. A high school kid could work them out from first principles, pointed in the right direction. One site which includes a form of this derivation is here, and it has some good links to other sites.
Once you've understood that, you can then apply the Lorentz transformations in as much or as little detail as you like to satisfy yourself that the circular train example doesn't put the slightest dent in special relativity.
I'll give you a hint though: imagine that the Earth is transparent. You're standing next to a circular train travelling near the speed of light. Look below your feet, at the train on the opposite side of the planet. At that point, it's not travelling towards you, it's travelling perpendicular to you. This means that there is no length dilation in the direction towards you. Which means that the radius of the train is unaffected.
So let's take that a step further and ask what it would take for the dilation of the train's radius to take place. Well, it would have to be travelling at least partially in the same direction as its radius for that to be the case. But it's travelling in a circle, so by definition, the direction of its velocity vector is always tangential to the circle,perpendicular to the radius. At no time does any component of the train's velocity vector coincide have the same direction as its radius. Therefore, there cannot be any dilation of the radius. (For bonus points, show why this still applies for an observer on the surface of the earth, rather than at the center.)
Perhaps this gives you some flavor of how these things naturally work out to avoid contradictions. No special tricks or selective application of rules are required. In your original post, you talked about inconsistencies "popping out". The very fact that theories like special relativity are easily able to cope with every special case and test case that is thrown at them, is an indication of what solid theories they are (again, see Kuhn).
Much of this stuff, and especially S.R., is very accessible to anyone willing to take the time and make the effort to learn about it. If you haven't made that effort, though, claiming that it must be wrong because you don't understand it only demonstrates your ignorance, it says nothing about the universe or the validity of well-tested physical theories.
As a matter of fact, the question is of the radius! I've found an explanation that should satisfy you. To be brief, under GR spacetime is curved, geometry is non-Euclidean, and the circumference of a circle does not necessarily equal 2pi*r. So the train can contract lengthwise without the radius changing.
Hey kids, there's only 5 days left 'til Yak Shaving Day!
The logic of this is very simple:
- Crackpot dislikes or can't understand theory.
- Crackpot has ultimate faith in own intelligence.
- Therefore, theory in question must be flawed.
- Therefore, it will be shown to be wrong in future.
It's actually a mechanism for maintenance of self-esteem. I suppose we shouldn't be so hard on them. "Forgive them, Albert, they know not what they do."Think of my example as a recursive example; my point is just because a triangle can be decomposed into three pieces is not a proof that the triangle doesn't exist. Apply the point recursively as deeply as you care.
Just because a real-world triangle may consist of untold quintillions of super-strings doesn't mean the triangle doesn't exist, it just means your human mind can't hold both frames of reference at the same time. It's a human limitation, not a universe-al one.
I take it you haven't studied non-Euclidean geometry. Here's an example:
Take a curved surface, let's say the size of Earth. Now, look at it from the perspective of two-dimensional beings on its surface. Draw a circle centered on the north pole with a circumference of 1,000 miles. Now measure the radius of the circle - on the curved surface of the Earth - and you will get a value slightly greater than the ~159 miles you would expect, because you aren't measuring on a straight line. The circumference is less than 2pi*radius.
Incidentally, if a degree is defined as 1/360 of a circle, you still see 360 degrees. Keep in mind, you have to bend your protractor to measure an angle on the curved surface.
Another interesting fact: on a curved surface, the angles of a triangle don't add up to 180 degrees. If you draw a equilateral triangle on the Earth with one points at the North Pole, and two points on the equator, so that each side is 1/4 the circumference of the Earth, all three angles will be right angles, and the sum is 270 degrees.
This is exactly what happens with the circular train. The circular motion (which is equivalent to acceleration or gravity) curves space in such a way that the track is non-Euclidean and the circumference does not equal 2pi radius.
Hey kids, there's only 5 days left 'til Yak Shaving Day!
I assume you're talking about a spinning ring around the earth? Of course as it went faster and faster it would be thrown apart by centrifugal force. At any point on the ring, each particle would be going straight at nearly 300,000 km/s. Within let's say 1/10 of a second (I don't feel like researching the diameter of the earth and figuring it out righ tnow), all of those particles are now moving at a different direction 90 degrees from their previous direction. All of that force will have to be absorbed by the ring. Anyway, none of the particles is moving in a reference frame, they're constantly changing their direction because they are spinning. If you saw a section of the ring move by at nearly the speed of light, you would measure it as smaller than if it were at rest. An observer in the section would also measure you as smaller then if he was at rest. The important distinction is that the apparent shrinkage occurs only in the direction of motion. i.e. the ring would still have the same diameter around the earth and each section would have the same height. Jason
"Do satellites contract"? From the point of view of an observer, their dimensions appear to contract along the relative direction of travel. The satellite itself detects no such contraction in itself, although it detects such contraction in you.
"Does the network of them contract?" It depends on the relationship of the observer to the network. See my answer re the train example. The answer will be the same as for a single satellite, i.e. contraction along the direction of travel relative to the observer, if the entire network is moving toward or away from an observer. If the observer is being orbited by a network of high speed satellites, then as I've pointed out for the train example, it's easy to see that there can be no contraction of the radius. So where's the problem?
"Is it visible in principle?" Certainly. All of these phenomena are visible, repeatable, verifiable, and theoretically consistent. They have been observed and verified in various ways. The problem is that to see obvious dilation effects that don't require very sensitive equipment (like atomic clocks) to measure, you need objects travelling close to light speed, which is rather difficult to arrange. Nevertheless, verification of the theory has been successfully performed in all sorts of ways.
Plus, no one really looks at other theories.
This is utter nonsense. Every serious scientist looks at all kinds off theories. (I have a PhD in prticle physics and concider myself a scientist).
Read Holographic Universe
Don't. It is not worth the paper it was printed on. This is NOT natural science. Science works: a) Hypothesis -> b) Experiment -> c) (no)Agreement -> someone else reproduce c) -> next Hypothesis.
Please notice the "Experiment" part. Just mumbling nonsense noone can prove and making experiments in your backyard noone can reproduce is NOT science. (This also means that those String Theorists have a big problem, cuz they cannon find something to measure, but they are aware of that and working on it)
Cheers, Peter
KdenLive/PIAVE - non-linear video editing
Given that this is because we haven't been able to construct a suitable experiment, what do you conclude from that?
Given the nature of the theory (which as I have pointed out, can be derived by a high school student), the fact that this one aspect hasn't been experimentally verified doesn't detract from the theory.
If the theory is wrong, then you should be able to come up with a thought experiment that challenges it. The circular train/satellite network is a nice try, but it doesn't succeed. So where does that leave you?
The problem arises, when all the wagons (let say 360 of them) are so contracted, that they _all together_ need only 1/100 of second to pass - instead 1/7.5!
You can't measure the length of the 'wagon' by the time it takes to go by when it's going by at relativistic speeds, because time and space are getting mixed up. Events which appear simultaneous to you do not from the perspective of the train, and vice-versa.
Nor me, nor the lions don't see any weird geometry around us - which had to save the SR.
And I don't see a train circling the equator at near-light speed. This is why relativity is hard to fathom - it doesn't match our normal experiences, because we don't generally see anything moving more than 0.001% of light speed. Nevertheless, every experiment ever performed to test relativity has indicated that these effects do occur.
There's a lot of great reference material on relativity on the web. You will probably learn a lot more searching it out than you will reading these replies on slashdot.
Hey kids, there's only 5 days left 'til Yak Shaving Day!
If you expect contraction of the radius, it simply means you don't understand SR. It's hard to refute something you don't understand. How could the radius possibly contract, when there's no motion in that direction?
If you believe the radius must contract because of contraction of the length of the ring, you need to consider the effect of constant changes in direction, i.e. the effects of acceleration. You seem to be trying to apply SR in a single step to the system as a whole, completely ignoring the effects of the construction of the example. No wonder your results seem inconsistent!
For example, how are you accounting for the fact that at different points along the track, train cars or satellites are moving in *opposite directions*? Oh, you're not accounting for it at all? Bit of a problem, don't you think?
Do you think, that there IS observable contraction:
- in this case?
I'd have to do the math to figure out exactly what would and wouldn't be observable in this case. In general, I would expect observable effects, but certainly not to the same degree as the noncircular case. As has been pointed out, including by this page, general relativity has to be considered because of the constant and extremely high acceleration in this example, and this has a significant effect.
in the case of noncircular train?
Yes, contraction in this case would be observable, because the motion is in a constant direction and thus the SR effect is not affected by continuous changes in direction; which means that GR can be ignored, incidentally making the calculation much easier.
I encourage you to try to work through the derivation of the Lorentz transformation, even in just one dimension. It will be much easier to understand all this once you've assimilated that.
That things, particles, whatever, behave mathematically (bouncing off each other, whatever) in a manner that fits a timestream, I don't see why people pedantically want to consider it illusory.
Yes, on a particle level, there is no difference in the direction of time. However, when you look at the larger picture with the "spread out" happening only in one direction...
"Has [being a kidnapped teenage girl, raped repeatedly for months] changed you?" - Katie Couric to Elizabeth Smart
Yes, but it's the important one from the "time does not exist" question.
Stastically, the pool balls bouncing around on the table probably won't meet at a perfect and sudden triangle rack with all momentum cancelled. Why should the balls follow mathematical rules that follow from a presumption of time? Seems like a waste for the universe to go to all the bother.
"Has [being a kidnapped teenage girl, raped repeatedly for months] changed you?" - Katie Couric to Elizabeth Smart
One of the stupidest things I ever heard about physics was that it refused to deal with the subjective perceptual experience (for example, the "green" you experience looking at a tree.)
These are a very real, existing, physical phenomenon. That it is "introspective" is a cop-out of physics.
AI has made little progress in that, either. Until better computers come along, they still can't get past the question of whether such perceptual experience arises as a physical phenomenon of the brain, or as a physical phenomenon of the data pushing the brain itself does. Note to the religious: pushing it into the spirit world only suggests an acompanying spiritual physics, sorry to say.
"Has [being a kidnapped teenage girl, raped repeatedly for months] changed you?" - Katie Couric to Elizabeth Smart
So which of the postulates Einstein used are you rejecting: the constant speed of light, or constant physical laws in all inertial frames? Or have you found a flaw in the derivation? Otherwise, you're just blowing smoke.
You expect what?
I expect the dimensions of the observation to be based on the spacetime path that light from the observed object follows to reach the observer. In the case of an object undergoing orbital acceleration, I expect contractions on a local scale, but the effects of GR are difficult to intuit. However, overall it's easy to see the cancellation effect, as I've pointed out.
But if we move out to the Galaxy dimensions - there is almost no acceleration.
You're either orbiting, or you're not. If you're orbiting, acceleration has to be large enough to support that. There's a ratio there that can be expressed as an invariant.
How do you know, that you are not observing a circular case, watching ONE car?
Playing with limits doesn't affect the overall equation. Any local effects would not affect the overall system, because of the factors I've already described. I'd be happy to accept a research grant to work this out in detail - it ought to be a straightforward calculation. A computer simulation of what an observer would sees ought to be quite possible.
It is ALWAYS some acceleration involved. The gravitation of a distant star - whatever. Do you suggest, that SR never holds?
Orbital motion implies a special set of circumstances in which different factors cancel out. I'd expect a difference between the orbital case and a non-orbital case. The orbital case involves accelerations significant to the calculation, by definition. In non-orbital scenarios, the relative effect of acceleration would be less.
http://www.sciam.com/2000/0900issue/0900scicit6.ht ml
I browse at +5 Flamebait- moderation for all or moderation for none.
Kevin: So, you're doing a little painting.
Dave: That's right Einstein. How'd ya guess? I mean, I was trying so hard to hide it. Huh Einstein?
Kevin: Listen, not everything that comes out of my mouth is the theory of relativity. So can the sarcasm.
Dave: Sorry, did I hurt your genius feelings?
Kevin: Walk away, walk away... you're the genius, he's a painter... you're clearly the winner here. You figure things out, he paints things up.
Of course I can. I see no reason why not. Why? Who says, I can't?
Erm, Einstein, for one. You're forgetting that time and space have no independent existence in relativity, and some things just don't work out the way you'd like. For instance, when your car is driving at 100 mph, the speed of light from your headlights is still c, not c + 100mph. Both you in the car and the hitchhiker on the side of the road will measure the same speed c for your headlights. This is extremely counter-intuitive, but it has been experimentally proven (Michelson-Morley experiment, measurement of speed of light is independent of speed of earth's rotation + orbit around sun).
Of course we do. Distant galaxies travel with 0.3 c or more.
But we don't interact with distant galaxies in a way that makes relativistic effects obvious. Besides, the expansion of the universe is in the GR realm, so the effects are a bit more involved than just time-dilation and shortening. Incidentally, the relativistic equation for redshift is different from the classical equation, and this provides yet another proof of relativity.
Which one indicated the shrinking?
Plenty of particle accelerator experiments have shown reactions occuring over larger distances than they could if the particles were at rest, indicating that distances are different in the moving particle's frame of reference.
Since you are obviously quite interested in the subject, you ought to do some more research and reading. If you'd like, post some questions on sci.physics.relativity newsgroup - the folks frequenting that newsgroup are quite a bit more knowledgeable on the subject than I am.
Hey kids, there's only 5 days left 'til Yak Shaving Day!
This thing all things devours;
Birds, beasts, trees, flowers;
Knaws iron, bites steel;
Grinds hard stones to meal;
Slays kings, ruins town,
And beats high mountains down.
As copyright owner of this comment, I authorize everyone to defeat any technological measure which limits access to it.
Easy
.r ^2
Speacetime geometry is altered - read up on non-Euclidean geometry
Basically
1 circle is no longer 360 degree's
Circumference no longer pi
I suggest getting Kip Thorne's Black Holes and Spacetime book - it explains it thoroughly
...Upgrade now to Schrodingers Dog...
Background MW?
Do you mean the microwave background radiation?
A
PS If you want I'll post the ISBN number for the Kip Thorne book - and another book on Superstrings as well
...Upgrade now to Schrodingers Dog...
Note that close to c, things would not simply look contracted paralled to the relative movement but rotated (which results in contraction of the projected length). It's hard to explain with words only, you can get a far better feeling for it by looking at the relativistic ray tracing simulations of a Flight Through Stonehenge.
This does not take into account all SR effects (e.g. the Doppler shift) and it does not take into account GR effects (it's also a straight movement, not circular) - but it still might help you to get a feeling for relativistic effects.
An overview of simulations of special relativistic flights can be found Andrew Hamiltons Homepage.