- Rotation of mass induces a twist in spacetime (but not a proper radiating wave). This is detectable by differences in orbits and swirling of masses near the source (transfer of angular momentum).
- Rotation of current induces a twist in magnetism (but not a proper magnetic field). This is detectable by differences in phase of electron beams around a solenoid (i.e.
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and anything else that depends on the magnetic vector potential A).
- Not all accelerations are radiating, though they are likely to "catch up" at some point. For example, this is why LINACs are preferred for fermions: synchrotron radiation is only emitted around corners (and bremsstrahlung on eventual impact), so the beam has lower losses traveling in a straight line.
- Note that a passing mass will give off a "wake", just as an electron does (space charge). Indeed, there are analogies: the gravitomagnetic force is a necessary consequence of a certain kind of approach to relativity (I forget if it's a consequence of using vectors instead of tensors, or if it's assuming 3D+time with a speed of light, or infinite speed of light, or what). I suppose there should be a gravitoelectric effect too; perhaps that would simply be mass itself, I don't know.
- Currently, we don't know of a source of negative mass (and, so far, it appears that antimatter still has positive mass). Which might perhaps be analogous to the lack of magnetic monopoles in E&M / QM. In any case, with only positive mass charges, only quadrupole sources can radiate: the alternation of two positive masses (and the relative drop in gravity when those masses are perpendicular to the detector, versus the rise when collinear with it) provides such a source. Which, of course, is quite likely what was famously observed a few days ago.
Relativity is basically an extrapolation, expanding E&M to all of spacetime; it begins with the idea of Lorentz invariants (which arise necessarily in E&M: a transformer works by time-dependent fields, just as well as by space-dependent fields, which we usually call motors), and fleshes out the idea. Along the way, tensors are used, which I would think (not being an expert on relativity myself) can express rotation, spin, shear and all that, quite naturally (i.e., with a skew-symmetric pattern). So these phenomena are no problem to represent.
As far as I know, E&M can also be expressed in tensors, though it's usually simple enough in vector calculus (4 equations in R^3, plus time), which is also easy enough to work with, so there's no need to use any higher level. When expressed with tensors, only one equation is needed, and it's much simpler than General Relativity's equation.
So it should be no surprise that there are many similarities. The only problem remaining, really, is we have no freaking clue what a "graviton" might look like. Presumably, they are massless bosons, and follow the same frequency-energy relationship as photons: the max ~kHz waves observed from merging black holes implies we need a detector cooler than ~0.1uK to even begin to observe shot noise:
As for dark mass, what it is, is currently unknown. It is used to explain the anomalous motion of galaxies and clusters, which seem too massive given the mass we see in them. Presumably we will eventually find what it is (tremendous amounts of cold neutrinos?!), and it will become clear what the problem was. Likewise, "dark energy" is used to explain the curvature of space _that occurs despite the amount of mass we observe and infer_. In other words, an expansion constant (probably not actually constant) to correct for the observed expansion of things.
As far as I know, dark matter and energy are not essential consequences of relativity (not like, say, gravity waves), but are used to correct our models that implement a subset of relativity (as far as I know, few simulations or analyses invoke the full equation, preferring a simpler metric like the Minkowski; but again, I might have that very incorrect).
Not exactly true. The "spacetime fabric" is an expression of Einstein's Gerneral Relativity, known to cosmologists and astronomer as 'gravity' in current physics.
Grand unification of gravity and EM (and the strong and weak nuclear forces) was not acheived by Enstein nor by modern whiz kids. String theory does not work and current work on GUT is most hopeful with "loop gravity". See Wikipedia.
Electro-magnetism was derived by Maxwell and is encapsulated in the Maxwell equations. While the electromagnetic force has been unified with the strong and weak nuclear forces, that is of no relevancee to you. Electromagnetic waves derive from the electromagnetic force as in Maxwell's equations. Magnetism and electric force are "unified" in Einstein's Special Relativity, but that is of no relevance to your argument.
In this forum one needs authority to avoid argument. In order to prevent dementia of the old, I am currently enrolled in cosmolgy and astonomy at the local university. I am an excellent student. In addition, in a former life I earned a B.Sc, M.Sc. and Ph.D., worked in engineering and taught electricity and magnetism at the senior high school level.
In summary, don't nitpick me, read Wikipedia. My answer is meant to educate not to provoke argument.
The best description yet that I've heard for dark matter and dark energy started with "I really don't like those names, but they do sound better than 'we don't know what the hell is going on but we do know it's happening'".
The important thing about relativity (and quantum mechanics, mostly) is that however wacky it may sound, it WORKS, and competing theories either don't work, or work but don't make any testable predictions beyond those of the theories they're trying to replace.
Dark energy and dark matter haven't been accounted for in the standard model of particle physics. The mass of the Higgs boson is too light according to the standard model. So the standard model will probably need to be added to somehow -- but it'll almost undoubtedly be changed within quantum mechanics.
I'm a bit out of date on this stuff but was under the impression that gravity is a property of ALL massive objects, not merely those of accelerating mass.
AFAIK, changing electric charge will generate an electric field; the magnetic component of EM requires a changing *current* in addition.
For "gravity waves" I meant AC gravity waves. A stationary mass can have a charge, an accelerating mass can have a charge, an accelerating mass with a charge emits gravity waves and electromagnetic waves, while an accelerating mass with no charge just emits gravity waves.
A stationary mass with or without a charge has gravity but doesn't emit any gravity waves otherwise it would decrease in mass from the energy lost.
So a stationary mass has zero energy emitted in gravity waves, but has a "gravitational charge", just like a magnet in electromagnetism.
My pet theory is that the need "dark energy" (and possibly also "dark matter") will disappear in a modified theory of gravity. Dark energy is currently just a fudge-factor added to relativity in order to make the numbers work out for the observed curvature of the universe. My hope is that someone will figure out a new model that is more accurate over longer distances than relativity, just as relativity refined Newtonian gravity. Perhaps we will learn about the quantum nature of gravitons, and see that it has implications limiting the distance of effect of gravity - weaker gravity over very long distances would have a similar effect to "dark energy". Bonus points (and probably Nobel prizes) for any answer that also explains that other glaring fudge-factor, inflation.
Dark matter is needed even in the classical Newtonian limit since galaxy rotation curves are too fast compared to the amount of mass that can be accounted for by the visible light of stars. They ought to fly apart if the only thing holding together was just the stuff we can see.
Dark matter used to include anything that was not luminous matter (ie. everything that isn't a star or brown dwarf). Back in the early days you could hide it as biros, chair legs and sticks of rhubarb. But today with the extended range of observational wavelengths there is nowhere left to hide ordinary baryonic matter in sufficient quantity. There has to be some form of cold dark matter that really doesn't interact at all by electromagnetism (or at the very least a functional equivalent that we haven't done the right experiment to discover yet).
Dark energy is another kettle of fish. That was the constant of integration that Einstein original put into the Einstein-Lemaitre universe solutions to permit a stable steady state solution - something he described as his greatest mistake when experimental evidence for the Big Bang cosmological model made it obvious that Steady State was wrong.
It is curious that we now find that the value has to be slightly non-zero to match the observed boundary conditions in our universe!
I confess that I don't much like dark energy. I would much prefer that something was funny about the earliest supernovae in the universe.
Basic relativity is just a consequence of requiring that the laws of physics should be the same for all observers in an inertial reference frame. The hints were there for all to see from the point where Maxwell's equations allowed the electromagnetic wave equation to be derived but it took Einsteins genius to spot how to make everything work correctly together as coherent physics rather than ad hoc fixups (various others like Fitzgerald, Heavyside, Poincare, Lorentz and Larmour had partial solutions).
We can never be sure of that. Whenever someone announces that physics will be completely solved in X years some exotic experiment gives results that refutes the status quo and a paradigm shift occurs.
What is certain is that the current models are not quite right since there is still no way to combine the quantum physics of the very small with large scale physics of general relativity (a continuum theory).
Both theories in their own domain have been verified and validated with unprecedented accuracy and precision but there is a no man's land in between them where things still get very tricky.
What's peculiar is, AFAIK, QM has been hacked to even use special relativity; indeed, this is what made QED possible, and it's as accurate as we can measure (and QCD is as accurate as we can model, so it seems; it's just ridiculously hard to work with).
No, it's also needed to explain the rotation curves of galaxies. If the mass of the galaxy were concentrated the same way as its luminosity (i.e. strongly towards the centre) then the outer parts would show Keplerian orbits (period proportional to (semimajor axis)**1.5), but they don't. That's where the dark matter concept originated. Other things, e.g. the cosmic deuterium abundance, show that the dark matter can't be baryons, and a theory of gravity that deviated badly from Newton over a hundred kiloparsecs or so wouldn't fit the cosmological data.
Clearly there's a lot more to learn. My son Simon (aka Dashing FPGA Hunchback) is working on a dark matter detection experiment (DEAP) at TRIUMF in Vancouver. Whoever detects it first will probably get a Nobel too.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
No, the Dirac equation has been around since the 1920s. (It's the special-relativity version of the Schrodinger equation.) Feynman's method (those funny diagrams with virtual photons and so on) is a method of keeping track of all the perturbation integrals.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
AFAICT the gravity lensing from the bullet nebula and other galaxy collisions has put an end to most modified Newtonian gravity theories. (though you have to wait for the old theorists to die... :^)
Dark matter is the big mystery now, it must be a fun thing to work on.
Yes, he's graduating in Honours Physics this May, God willing. He's got a job at TRIUMF after graduation, which is good since he wants to take a year to decide on a grad school.
I think that's right. There isn't as much wiggle room to dork the higher-order terms as there used to be, e.g. the old Brans-Dicke scalar tensor theory.
He's in charge of 240 photomultipliers, each with its own digitizer, PSU, and FPGA. He's basically rewritten the timing and control FPGA code from scratch, I gather. He's got chucked in the deep end, for sure--he had to learn HDL coding from the ground up. The deep end can be uncomfortable at first, but that's how you get to be a wizard.
Cheers
Phil "Proud papa" Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
It's always a moment of pride when you off-spring perform up to expectations.
Our _fifth_ granddaughter graduated from UofA in December (early).
All five were employed prior to graduation.
None are engineers :-( All are honor graduates of the Eller College of Management (business). ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Since gravitational effects travel at light speed, it seems to me that the field created by rotational frame dragging should be capable of becoming some sort of transverse wave, sort of like a gravitational compression wave. Poke a stick into a spinning wheel and the frame-drag field gets shut off, so there is some sort of wave effect.
The critical issue is that gravity travels at c, as Einstein predicted. Pretty smart guy.
Does a traveling mass radiate a gravitational wake and thus lose energy?
--
John Larkin Highland Technology, Inc
picosecond timing precision measurement
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Great! A year off doing some research may help him figure out what he likes, (if he doesn't already know.) My advice would be to try and pick an advisor and not a grad school... but that may be hard... again depending on his interest. And if he's good he might be 'scooped up' by some prof where he's working.
"Woosh....", The sound of a GR reference passing far over my head. :^)
Sounds like he's already got his head above the water.
Grin.. and being able to "talk shop" with your son is an added bonus. My daughter will be a senior in HS next year. I tired to convince her to take an optional math class, but she, "hates math". She did sign up for physics though.. (I think somewhat to keep her dad happy.) which I warned her will still have plenty of math.
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