Slashdot Mirror
Purported Relativity Paradox Resolved
sciencehabit writes "A purported conflict between the century-old theory of classical electrodynamics and Einstein's theory of special relativity doesn't exist, a chorus of physicists says. Last April, an electrical engineer claimed that the equation that determines the force exerted on an electrically charged particle by electric and magnetic fields — the Lorentz force law — clashes with relativity, the theory that centers on how observers moving at a constant speed relative to one another will view the same events. To prove it, he concocted a simple 'thought experiment' in which the Lorentz force law seemed to lead to a paradox. Now, four physicists independently say that they have resolved the paradox."
The four physicists waived their hands over the box containing Schrödinger's cat while repeating, "omine, omine, omine" before walking away without looking inside and thus the conjecture was false and the paradox is resolved.
Science is alive and well in at least the Physics community. Whilst I won't even pretend to understand General Relativity, the questioning of it and discussion about those questions is the true essence of science. facts ->theory->more facts->questions->revised theory. Beautiful!
General relativity cannot clash with the Lorentz force law, because it is based on Lorentz invariance.
How strange that even I understand the "hidden momentum" concept (I think!). Time for a car analogy:
Imagine a car driving past you. At first you're looking at its front, then side, then it rear. So the car actually rotated from your frame of reference, and at the time it was passing right next to you it had an angular momentum.
Since the car was not actually rotating, those physicists call it a "hidden angular momentum".
This electrical engineer claims that such angular momentum is just a kludge concept added on top of relativity, and not real. If my understanding is correct, then he is wrong.
http://prl.aps.org/toc/PRL/v108/i19
:)
Scroll down to "Trouble with the Lorentz Law of Force: Incompatibility with Special Relativity and Momentum Conservation", there you can get the pdf, if you have university access. Whew, it took me more than 20 minutes to find it. Why those journalists do not include the cited source?!
This paper is actually quite interesting, and I remember my ED teacher complaining about the Lorentz Law incompatibility during his lectures too. Whether "hidden moment" exists or not - maybe is a matter of performing the right experiments
And what about the proton radius problem?
#
#\ @ ? Colonize Mars
#
Since a paradox is not a feature of the Universe; it is a feature of a limited mind trying to understand the Universe.
Didn't have access. What is this? Scientology? Have to advance in levels of priesthood or something?
RTFA. Unlike dark matter, hidden angular momentum isn't "invented", it follows from the assumptions of special relativity, which are dead simple and already proven beyond doubt.
Glad to see that others are noticing that in Physics we are still willing to entertain questioning of the foundations of modern Physics by those outside the field. Another great thing about our field is that most every paper is openly available on one of the abstract services. The original article noting the apparent paradox can be found here. While the subsequent discussion can be seen by looking at the papers citing the original, found here. Some of the commentaries have yet to be released from their embargo and are thus not yet available but will likely be so soon.
A purported conflict between the century-old theory of classical electrodynamics and Einstein's theory of special relativity doesn't exist, a chorus of physicists says.
Now, four physicists independently say that they have resolved the paradox.
If the four physicists spoke independently, how are they a chorus?
What ever means are necessary, in the quest for knowledge, the artificial imaginary made up, invisible laws made by man are just that, big fairy tales that dont exist.
Liberty freedom are no1, not dicks in suits.
Summary: Engineer misunderstands physics - physicists prove him wrong.
Where's the news?
So, hidden momentum and dark matter... What other concept will we invent to explain we dont know anything?
Dark matter is not an invented concept, it is a name for something we observe. Galaxies just rotate faster than from what is there in normal matter. So something is going on, and this something is called "dark matter", just because it does not produce/interact with light but behaves like a mass.
Now in what way you explain this (new physical laws, new elementary particles) is still an open question. But it's there and needs to be addressed. Dark matter is just the name of the problem.
NB: The message above might reflect my opinion right now, but not necessarily tomorrow or next year.
if you forget part of the energy-momentum tensor when you transform your coordinates from a stationary into a moving frame of reference.
Special relativity really cannot "clash" with the Lorentz force law, because it is based on the Lorentz invariance of Maxwell's equations. I think a "paradox" like this keeps coming up ever so often in discussions of special relativity, form people who don't understand it. I just don't see how PRL can accept such a paper.
I admit it would make a nice problem for a physics test, but not much more.
***Quis custodiet ipsos custodes***
First of all, this post is aimed not at the engineer from the article, but at some of the posters to this story and others like it. What is it about physics in particular that attracts so many uneducated crackpots? It seems to be the sweet spot for cranks on the XKCD spectrum--they don't go all the way over to math, and try to promote their pet tensor analysis theory ("this is how we really should compute the induced map on the cotangent bundle!"), and even less often are we treated to their "revolutionary" theories of hydrocarbon structure or ribosomal protein synthesis.
Nope, they gravitate straight to physics. Is it that concepts are (relatively) familiar, like light, gravity, time, particles, etc? Is it Star Trek? Must drive physicists nuts.
Yo dawg, I heard you like the Ackermann function, so OH GOD OH GOD OH GOD
Executive Summary
If you have a paradox in a thought experiment, you can think your way out of it.
"I believe in Karma. That means I can do bad things to people all day long and I assume they deserve it." : Dogbert
This reminds me of another paradox which is still unsolved. Even the experts disagree. Some claim (Feynman) it does not since it would violate relativity, but some (Becker) claim things would still work out. Even QED/QCD/QFT does not provide a conclusive answer to the above. Unfortunately it would take a billion dollar experiment to find out and since no oil is involved that is not going to happen.
When you go on dates with your girlfriend, do you pick up her check?
Do you buy her more gifts than she buys you?
In the overwhelming majority of cases, the answer to both questions is a resounding "yes."
She may not be billing you, but you are definitely paying her.
I think dark matter theory is a bit more presumptive than 'any theory to explain discrepancies between established theory and observed reality with respect to gravity' it specifically hypothesizes some sort of matter as the mechanism. For example there are theories suggesting our accepted model to describe gravity is incomplete and more complex models might explain the discrepancies. Of course the post saying dark matter is 'invented' does unduly trivialize the experimentation that is going on to attempt explanation and the strength of the evidence supporting the theory that it is a sort of matter versus incomplete models of gravity as an explanation for what we observe.
XML is like violence. If it doesn't solve the problem, use more.
One of the links leads to mit.
OR, and this is a big OR, our Theory of Gravity is off and needs fixing. I don't say this lightly because our current theory works very well. It is, however, not absolute and is still theory.
Observations of the gravitational lensing caused by far away galaxies in the process of merging have distinctly shown concentrations of something that's lensing the light that's not in either of the two galaxies. There are also other observations that kill any possible 'alternate law of gravity' explanations.
I thought these explanations were interesting myself and I've been paying attention to the topic. And there's been a lot of study of these ideas, because you're right, positing a brand new form of matter is a big step. And study leads to experiments. And the experiments have lead to the general consensus is that dark matter has to be something that has mass and doesn't otherwise interact with light (or normal matter) at all.
Need a Python, C++, Unix, Linux develop
Now in what way you explain this (new physical laws, new elementary particles) is still an open question. But it's there and needs to be addressed. Dark matter is just the name of the problem.
Hm. Doesn't calling it Dark Matter strongly imply that it is NOT a new physical law but rather some sort of... substance or particle? Surely you can see how the non-physicist who is curious could be mislead into a narrower interpretation?
"Someone needs to talk to the tree of liberty about its ghoulish drinking problem." by ohnocitizen
So, when we find a theory is wrong, we are not supposed to try to come up with new theories to replace them?
Dark matter is not an invented concept, it is a name for something we observe.
It is as observed as Aether or the cosmological constant...
The thing is, there are many teams of physicists working on modified theories of gravities or trying to find new modifications of gravity. So far, none of them work as well as the dark matter theory, and they contradict observations in some way or at some place (or possibly require both dark matter and a modified just gravity). Some of them are even more contrived than creating a new particle, because they have arbitrary distances where things just suddenly change and they have to get that distance by just fitting data. Even some of the physicists working on and promoting such new gravity theories admit they are inelegant or still not as good as dark matter. But they all work on it just to be sure there is not another possibility hidden there.
Dark matter is not an invented concept, it is a name for something we observe.
Precisely the opposite - it's a name for something we haven't observed. And instead of appropriately referring to it as a paradox, inconsistency, etc. a concept of an entirely new "matter" was conjured up. I might agree with you that it's more likely that something is missing in the estimates of galaxy masses as opposed to physical laws breaking down, but gp is perfectly correct in saying that at this point it's a theoretical (i.e. invented) concept.
but gp is perfectly correct in saying that at this point it's a theoretical (i.e. invented) concept.
So are quarks. They were invented to try to explain patterns seen in the formation of hadrons, and later used to explain some aspects nuclear structure. We don't observe the quarks directly, but only their interactions and decays. It is still possible we've missed another explanation that doesn't require inventing a whole family of particles.
The only thing that matters in the end is how well the theory agrees with observation. Dark matter is kicking butt here compared to all proposed alternatives. Although it has a ways to go to at same level of say quarks.
Of course, the increase in speed from other galaxies is caused by aliens who are trying to fool us so that we don't develop superior knowledge.
In physics, if you have two explanations for a problem, choose the simplest one. If you have only one, well, that must be it.
If Pandora's box is destined to be opened, *I* want to be the one to open it.
Photino birds?
"I do not agree with what you say, but I will defend to the death your right to say it"
You're about 5 years behind the facts on dark matter. The cosmic microwave background radiation studies comfirmed the dark matter hypothesis for galaxy/cluster rotation rates several years ago now.
Dark matter was proposed in the 1930s. At the time it was one of several hypotheses for why rotation rates weren't as expected. But a few years ago the CMBR studies also "observed" dark matter, and the matter/dark matter ratio matched the predictions to a couple of significant digits (which for cosmology is amazing).
The existance of dark matter is now confirmed as much as anything can be in cosmology - the evidence is as strong or srtonger than, say, black holes existing.
Socialism: a lie told by totalitarians and believed by fools.
Sorry, you're just wrong on this one. In the 1930s, then the hypothesis was new, you would have been correct, but in the past decade measurements of the early universe (via the CMBR) have directly confirmed predictions made by the dark matter hypothesis.
Dark matter is as confirmed as anything else in science that there's not actual engineering built around. Everything in science is a theoretical concept: that's not a useful statement.
Socialism: a lie told by totalitarians and believed by fools.
As an interesting aside, I remember hearing that someone recently analyzed galactic rotation in terms of General Relativity rather than Newtonian gravity and found that the "anomalous" speed curve is actually predicted by the theory (the math is apparently *much* more complicated, which is why it hadn't been attempted before). It's true that there have been other observations of phenomena that also support the Dark Matter hypothesis, but the reality may well be considerably more subtle than the universe containing massive quantities of non-baryonic matter.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
The name of the problem is Dark Matter! Dark Matter.... or Dark Energy.
The name of the two main problems are Dark Matter and Dark Energy... and hidden momentum.
Our three main problems are named Dark Matter, Dark Energy, and Hidden Momentum.... and Inflation...
Amongst the names of the main problems are Dark Matter, Dark Energy, Hidden Momentum, and Inflation....
Wait, I'll come in again.
Galaxy rotation curves are one of the things heavily studied by modified gravity theories. Some of them can fit the rotation curves, although there is a question of whether it is over-fitting, and such theories usually fail to match any of the other observations tied to dark matter.
No, it's not about facts.
It's about epistemologies: How you arrive at those facts. Most scientists follow an empirical empistemology. The rest of the world usually follows a more rational one, or historical (i.e. something is true because a book says so).
A rational epistemology holds that anything that can be proved logically is true. An empiricist holds that anything that can be demonstrated experimentally is true. Some statements can be true in either paradigm, but it can make a big difference as to how you arrive at these conclusions.
And it's not that either is necessarily invalid, or even that they're entirely separable. You have tradeoffs: with rationality, you can prove things that aren't necessarily 'true' in the real world. With empiricism, your truths are only valid to the limits of measurement: there's very little in the way of absolute truth to be had.
The clashes between science and the church were epistemological. Only one of these things can be the ultimate test of knowledge. So far the empiricists are winning if you count the fruits of their works, and the rationalists are winning by sheer numbers.
Those who advocate genocide deserve every protection afforded by law, and none afforded by common human decency.
Well, a new substance or particle that creates the observed effects of dark matter would very likely require new physics. For example, there is no dark matter candidate particle proposed by the Standard Model, though other theories and modifications of the SM do propose possible DM particles. These would be new physics.
Not a sentence!
Mansuripur's papers are readable on Archive.org, while the replies of his critics are on paywalled journals. I do not have 30 or 40 dollars to observe their handwaving. Since he's out in the open, while their supposed 'replies' are hiding behind the bulwarks of protectionist convention, I'm awarding the decision to Mansuripur. All hail Swartz.
"You must try to forget all you have learned. You must begin to dream." -- Sherwood Anderson
Sounds murderous indeed.
But seriously what do you mean? You think gravity is all figured out? Does that mean we have unified the 4 forces? Care to put the matter to rest with some cut & paste, or a link or two?
We have the _effects_ of gravity mostly figured out but how, for example, do you think gravity actually works?
If dark matter doesn't interact with light, then how does it cause gravitational lensing?
It interacts gravitationally. What it apparently does not do is emit or absorb light.
I guess Einstein was wrong!
Shit, we'd better fire all those Physicists who use Relativity to do important and socially useful things. Like... all the job's they've created for high energy physics experiments since WW2.
Oh, wait, never mind - they're all sure they're right, and this guy must just be another crackpot. After all, it's not whether the idea is sound and stands on it's own merit and truth that counts. It's how popular it is.
Gee, suppose we just rated theory by it's usefulness to engineering? After all, if it really is a better understanding, it should enable entirely new applications.
Eg: Can somebody tell me why a simple and efficient 1 moving piece linear actuator (an electromagnet) doesn't have as much power-to-weight as a complicated rotating motor? And why is it that all texts on practical and detailed electric motor engineering drop even Maxwell's equations for the older and supposedly superfluous formulations of Ampere's and/or Faraday's laws?
Why is it that in any modern physics text, when introducing Maxwell's equations, there's always a "fast one" which says something like "the partial time derivative is just as good as the total time derivative that Faraday's law had, because nothing is moving so it's a good approximation."
Once the superiority of ME's are demonstrated, all these texts then go on to introduce the Lorentz force law "for a moving charge which itself is too small to effect any change in the fields, which are themselves calculated as if all (can only be) at rest".
It turns out this was pointed out a while ago, and fixed too. But clearly the approximation "That nothing* is moving" is pretty good for particle accelerators. Heaven help us if we ever need to build such a device with enough flowing charge to break that. Such a device which might stand a slight chance of harnessing Fusion directly.
Oh never mind, that's just 50 years away - and we'll just use such a strong field (ITER) that the approximation still holds... and never mind about all these strange instabilities that happen in every single Tokamak that's ever been run hard - I'm certain that it MIGHT work if we just build one big enough...
(* where "nothing" is the approximate ratio of the mass of the moving parts to the rest of the mass of the apparatus.... Things like antennas, wires, etc. But not things like electric motors (the wires are moving.))
And you wonder why Einstein practically committed suicide (refused surgery) saying "...I've done enough (damage)." Hell, he did in fact figure it out before he died, but by then he was "going senile" according to the professional physicist community. He was a victim of his own cult of personality - everyone who have him props liked his image, but stopped listening when he tried to come clean.
They were really in love with his "smart guy" image. They didn't want to hear him admit that he forgot to check the bounds of validity of the theory he based his work on. "Explicitly Not for anything moving". Same thing happened to the guy who invented Coax - spent his entire life playing with telephone systems, and never concerned himself much with electric motors or moving coils. Of course his intuition was wrong! But that's a different thing from forgetting to do your basic homework... something like checking the instruction label and warning disclaimer first.
PS: Look up T. E. Phipps, Jr.
He's fixed it, result: Time dilation only, no length contraction, no Lorentz force law needed, space time OF COURSE is flat, and one can actually use Newtonian dynamics perfectly reasonably, so long as one compensates one's clock.
(Phipps provides an equation to allow a "motion corrected" clock, such as might be used with an atomic clock plus an intertial navigation unit, so that the completely arbitrary choice of "reference" clock can be tracked. )
Oh, and all those odd "paradox" problems just vanish - they were only showing up because the whole system was inconsistent anyway.
"In your face, engineers !"
-- Physicists
The three laws of thermodynamics:(1) You can't win. (2) You can't break even. (3) You can't even quit.
Loved that series of books
"Spooky action at a distance"
It's just called matter because it ACTS like matter, except for neither blocking or reflecting light, which is why it's called dark.
It's important to name something, even before you know what it is, because it's very difficult to discuss something that has no designation. They could call it "Effect 32" for all it really matters, it's just that "dark matter" gives the listener a little memory advantage over some arbetrary non-discriptive designation.
In reality dark matter could be nearly anything, and could be nothing like matter. Or it could be actual invisible matter that you could build things out of.
Don't get stuck on the semmantics of the phrase. Yes, it's an "I don't know", but it's a specific "I don't know". To just call it something mysterious, without an attempt to figure it out, would be the equivilant of writing "Here be Dragons" on our maps, and walking away.
THINK! It's patriotic
Neither of those concepts are part of modern science.
You fuss because he was not specific enough. He meant that "Dark Matter is an effect we observe."
I will not engague you in a debate on whether or not an effect is a "thing" in that context, but I suspect you knew what he meant.
THINK! It's patriotic
Aliens!?
No, no. It's Gnomes following their 3 step plan!
Step 1: Speed up the rotation of the galixies. .... umn.
Step 2:
Step 3: Profit!
THINK! It's patriotic
Indeed - however in this case we're not applying exotic theories, we're simply applying our best accepted model of gravity (GR) instead of our known oversimplified model (Newtonian) and finding the problem disappears, at least mostly. Given that, the rotation curves can likely no longer be used as an argument for dark matter, and in fact may be an argument against it since the presence of such matter is probably inconsistent with the observed rotation curves under GR.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
For those not interested in the fine detail, there's a very simple explanation as to why there isn't any real paradox involved.
Let's start with a quote from the article (looks like the paper is a bit more subtle, but the upshot is the same): "Now imagine how things look from a "moving frame of reference" in which the charge and magnet both glide by at a steady speed. Thanks to the weird effects of relativity, the magnet appears to have more positive charge on one side and more negative charge on the other."
Now, it's true that there's an electric field, and for many purposes it is convenient to imagine that this is due to charges on either side of the magnet. But these charges are fictitious. They aren't really there, as can be easily shown by observing that charge is a scalar, and hence the charge distribution in the magnet cannot be dependent on the frame of reference. Since they aren't there, it's hardly surprising that the external electric field doesn't apply a force to them.
So, basically, a fiction that happens to be convenient in electric engineering is incompatible with relativity; or, if you prefer, in order to make fictitious charges compatible with relativity you also have to have fictitious angular momentum. I'm not sure whether this is a big deal for electrical engineering or not but it certainly isn't any sort of deal as far as fundamental physics is concerned.