E=mc^2 Verified In Quantum Chromodynamic Calculation 268
chirishnique and other readers sent in a story in AFP about a heroic supercomputer computation that has verified Einstein's most famous equation at the level of subatomic particles for the first time. "A brainpower consortium led by Laurent Lellouch of France's Centre for Theoretical Physics, using some of the world's mightiest supercomputers, have set down the calculations for estimating the mass of protons and neutrons, the particles at the nucleus of atoms. ... [T]he mass of gluons is zero and the mass of quarks is only five per cent. Where, therefore, is the missing 95 per cent? The answer, according to the study published in the US journal Science on Thursday, comes from the energy from the movements and interactions of quarks and gluons. ... [E]nergy and mass are equivalent, as Einstein proposed in his Special Theory of Relativity in 1905." Update: 11/21 15:50 GMT by
KD : New Scientist has a slightly more technical look at the accomplishment.
Mathmatically verifiable (Score:3, Interesting)
As I understand it there were several geocentric models of the universe that were mathematically validated.
Am I mistaken or, doesn't that just mean that our theory matches all the known data and the data matches the theory. It Really doesn't have anything to do with whether or not the theory expresses reality.
Dark matter (Score:2, Interesting)
Since the missing mass is from the movement, does this mean anything in the search for dark matter?
Photons (Score:1, Interesting)
Could someone please explain to me why photons don't have mass but do have energy (Photons [wikipedia.org])?
Higgs Boson? (Score:3, Interesting)
I could be totally wrong, but I was under the impression that all the 'missing mass' of subatomic particle was believed to be generated by the Higgs Boson/Field.
Re:Pretty cool (Score:3, Interesting)
Re:Silly question... (Score:1, Interesting)
Energy isn't 'lossy'. The amount of energy (or energy and mass) in the universe is constant.
> What is to say that the energy produced from the interaction is always the same?
Nothing.
> If not always the same, it implies that the mass of neutron may vary over period of time!
It does. In accordance with the uncertainty principle:
deltaE * deltaT >= h-bar/2
Since E = mc^2, you can rewrite that in terms of mass:
deltaM >= h-bar/(2 * c^2 * deltaT)
Where deltaT is the period of time and deltaM is the varation in mass. This applies to everything in the universe equally of course.
When you calculate a quantum-mechanical property, you're always talking about the _expectation value_ of that property. Simply put: The statistical average.
> Btw, the article doesn't care to summarize how the super-computers were used in the proof (except for that last quote in the article).
Well.. not much to say. I involves solving the Dirac equation (the relativistic version of the SchrÃdinger equation). It's a big-ass partial differential equation. As the article notes, they're using a lattice of fixed points. So essentially it's a Finite-Element method, which is a common way of solving differential equations numerically. (Since most of them can't be solved analytically)
completely bogus interpretation (Score:5, Interesting)
The article at theage.com gives a completely bogus interpretation, which is repeated in the slashdot article. The New Scientist article is much better.
This is just total scientific illiteracy. E=mc2 has been verified over and over again. We see it, for example, in processes like alpha decay, where the sum of the masses of the product nuclei doesn't equal the mass of the original nucleus. Mass is converted into energy in that process, and that's been experimentally established since probably the 1920's. Likewise energy can be converted into mass, as when cosmic rays hit the atmosphere and create electron-antielectron pairs. The theoretical foundations of E=mc2 are also extremely firm; it's deeply linked to the basic logical structure of relativity, and relativity has been abundantly experimentally verified.
Saying that this calculation verified E=mc2 is just stupid. The calculation assumes (1) special relativity, (2) quantum mechanics, (3) some technical stuff about how to make special relativity and quantum mechanics work together (generic ideas about quantum field theory), and (4) a bunch of very specific technical approximations needed in order to get an answer out of this particular flavor of quantum field theory (lattice QCD). The calculation has a bunch of adjustable parameters (quark masses, coupling constants). You play with the adjustable parameters and get a bunch of numbers out (neutron and proton masses, etc). If the number of adjustable parameters that goes in is m, and the number of experimentally testable numbers that pop out is n, then n-m is the number of degrees of freedom that verify whether the calculation is right. (For n=m, it would just be a complicated exercise in fitting the data, like putting two points on a graph and saying "look, it's a line!") I assume they calculated more than just the mass of the proton and neutron, because otherwise n=2 would be less than m. I assume the n-m degrees of freedom checked out fairly well, because they're calling it a success.
To see why this calculation can't really be interpreted as a test of E=mc2, you have to imagine what would have happened if it had turned out wrong. If it had disagreed with experiment, then we would conclude that some of the assumptions built into it were wrong. Let's look back at the assumptions 1-4 above. Well, 1 (special relativity) has been verified a zillion different ways since 1905 (or even as far back as the 19th century, the Michelson-Morley experiment, with hindsight). 2 (quantum mechanics) has likewise been verified a zillion different ways since the 1920's. 3, the general framework of quantum field theory, has some ugly spots, but it's been used to verify things like the magnetic moment of the electron to a dozen decimal places, so it's still on fairly firm ground. 4 is extremely shaky; it's only very recently that anyone has claimed to be able to calculate anything at all useful and realistic with QCD. So if it had failed, no physicist in the world would have interpreted it as evidence that assumption 1 (relativity) was wrong. They would have interpreted it as evidence that assumption 4 was wrong: the lattice QCD approximations weren't good enough, probably for very boring, technical reasons that would only be of interest to a specialist in lattice QCD.
Funny. This Java script doesn't need supercomputer (Score:3, Interesting)
Use Heim Mass Calculator [daimi.au.dk] to easily compute masses of proton, neutron, electron and a lot of other particles as well, with a great precision (relative errors less then 0.00001) when comparing with most precise laboratory measurements available. The only hardware you need is Java in your browser.
This algorithm is based on 50-year old equations of Burkhard Heim thanks to his beautiful theory [wikipedia.org]. Notice that it include computation of neutrino mass which was found in recent years. When Heim was working on his theory almost all scientist were sure that neutrino is massless. The only input which this algorithm needs is a bunch of well known constants: h (Planck's Constant), G (Gravitational constant), vacuum permittivity and vacuum permeability.
Our current "mainstream" (hate this word) theory known as Standard Model is full of inconsistencies which are forcing scientists to constantly mumble about "dark mass" and "dark energy" stuff.
It remembers me about Enrico Fermi's comment "Beautiful theory, wrong universe". Does it apply here?
Re:Mathmatically verifiable (Score:4, Interesting)
Hadn't heard of him before. That is truly fascinating. It almost appears to have come full circle.
Prior to Galileo, scientists never made the assumption that their theory actually had correspondence to reality. They were mostly concerned with whether or not it corresponded to the data and considered a theory 'true' if it corresponded to the existing data and had predictive power. There was a phrase which was used to mean that but I can't remember it right now.
'conservation of aspects' 'preservation of aspects' something like that.
I once read a work by Hippocrates called which I believe was titled: 'advice to traveling physicians'
In it he begins by explaining that a traveling physician should take into account the environment of the town he is about to enter, because it will help him predict the type of diseases likely to exist in the population.
He then enumerates different environments and diseases.
For example he predicted , correctly , that people living in areas where there were 'strong seasonal winds' --- I assume monsoons, had a higher number of stomach related ailments. He noted this was most likely because they tended to drink brackish or salty water. He then explained that the reason for the stomach problems was because the salt made their heads soft and caused the phlegm to run into their stomach, which also explained why they tended to be much stupider then the rest of the world.
I think it makes that makes an interesting example how the 'testable' part of a theory can be completely correct and useful for predictiveness and the 'un-testable' part of the model can by wholly wrong.
That being said there are a lot of people trying to do silly things like , prove God does or doesn't exist using science or prove people do or don't have immortal souls or free will.
The problem comes in of coarse with testability and shows that science, while incredibly useful as a tool to the race, simply has it's limits which it is unlikely to easily transcend and are of coarse tied to our ability to gather, and interpret data.
Questions like whether or not God exists are simply outside the realm of science proper, because of the ability to gather sufficient and repeatable data with proper controls.
That includes, however, both the positive and negative answer. I have never quite understood the instance, some people seem to have, that you cannot prove God exists while insisting it is possible to prove he doesn't.
Re:Pretty cool (Score:3, Interesting)
Einstein may have demonstrated that the math had to be right, but this sort of result was needed to demonstrate that the math correctly described the universe.
By proving it hypothetically with another mathematical construct, aka a computer simulation? To my untrained mind, this sounds like proving 1+1=2 by typing it into Python and getting the expected result. Since these researchers obviously know more about this than I do, I'll assume the problem is with my lack of understanding. So, why is this simulation a valid demonstration?
Using mass to test Quantum Chromodynamics (Score:3, Interesting)
Okay, so here's my take on all of this.
First, here's a different spin on what E=mc^2 actually means. What it says is that if you want to measure the total internal energy of some object (i.e., the part that is independent of its kinetic energy), then all you have to do is measure its mass. This is actually a very remarkable fact because it says that you don't have to know anything about it's internal structure; instead, you only have to know one of two things: A) its weight in a gravitational field of known strength, or B) its acceleration in response to a known force. (The "equivalence principle" asserts that these two very different experiments actually measure the same quantity.) So in other words, you can take this "black box" and do an experiment on it that tells you its full internal energy.
Because of this, since we have done experiments of type (B) to measure the mass of the B_c meson (the particle of the article), we in principle already know its internal energy. However, in addition to knowing its mass, we also have a theory -- Quantum Chromodynamics -- that claims to tell us exactly what its internal structure is. One way to test this theory is be seeing whether the total energy it gives us of the particle is equal to what we measured via. its mass.
To see this in a different light, suppose that we were trying to figure out how much energy is in an oscillating spring, and the only measurement tool we had was the ability to weigh the spring very, very precisely. Then if we thought we had a theory for how much energy the oscillation contributes to the spring, one way could verify it would be by measuring the weight of the spring before and after we start it oscillating and checking whether the difference matches our independent calculation of what the energy should be based on our theory of how the oscillations work.
This is the spirit of what this calculation does. We know that the meson consists of two quarks, but like a spring there are all sorts of crazy oscillations going on that we are also trying to understand precisely. So given that we know the mass of the quarks, we can check to see if our theory of how much energy the "oscillations" contributed by the gluon field agrees with the mass of the meson (which is very roughly speaking, quarks + oscillations); of course, this alone doesn't tell us that Quantum Chromodynamics is the correct theory of nature, but if we didn't see agreement between the two calculations then we would have to re-think our theory.
The thing is, actually sitting down and calculating exactly what these oscillations contribute to the energy is very hard, which is why it has taken people so long to actually succeed in doing it. Now they have an answer: our theory does indeed predict the same quantity we see in nature, so in this respect it is not obviously wrong. :-)
Re:I've only got one thing to say... (Score:2, Interesting)
Newtonian mechanics are not "wrong", they are an approximation that matches the relativistic equations when the gamma is small. The error is far far less then any uncertainty in your measurement.
For example, try finding the length contraction of a 3 meter long car traveling at 60 kph using google calculator: [google.com] The result just gives you 3 m! :)
Re:I've only got one thing to say... (Score:3, Interesting)
There is no frame of reference in which Newtonian mechanics is correct. How objects are moving has nothing to do with what frame of reference you choose to use. You can choose a frame which is at rest with respect to one or more objects, but you don't have to, and your choice is irrelevant to the laws of physics.
Whether E=mc^2 is valid for a non-stationary argument depends on how 'm' is defined. That symbol has been used in more than one way in the literature, although your usage is now the most common.