Ask any question you want about Physics

originally posted by: ImaFungi
a reply to: joelr

I know everything you know about theoretical fundamental physics, but more. I have all your understandings and perceptions of models and reality in my head, but the more intelligent progression of my thought, has resulted in viewing such stances as far from accurate/complete comprehensions of actual reality.

Are you The Donald's science advisor too? He may have an opening.

originally posted by: mbkennel


As I understand it (we need Eros for confirmation), the notion of "virtual particles" comes about when you try to do many computations in quantum field theory, and you need to make a "perturbative expansion".

In principle, Nature solves the true underlying field equations in full nonlinear form. Which humans approximate up to a certain order of expansion (think of approximating a function by a series expansion in some region around a known value).

In this expansion there are terms which are identified as 'particles' by their mathematical structure and the connection to physical experiment. The real ones were identified, and then there are other terms, in the math which look like real particles (but aren't exactly), and these are called "virtual particles".

Down at the core, there is the underlying field theory which is the TRVTH as far as we know it. Then there are approximations so primates can connect to primate experimental results.

Analogy: to do Maxwellian classical electrodynamics, you don't need virtual particles. You just solve the underlying partial differential equations. But when you do it on a computer, you have to, in practice, make some grid of 'finite elements' and patches of 'fields'. These are the expansion functions, in a sense, of a practical electromagnetic simulation. They aren't the underlying truth, they are the computational convenience.

In a rough analogy, these are equivalent to real and virtual particles. In electromagnetic interactions, real particles (photons) correspond to radiation which can transmit energy & momentum out to far distances. The virtual particles are the expansion representation for non-radiative (near field, in the classical sense) electromagnetic forces like induction, etc.

Yes, Maxwell's equations and classical electrodynamics is a field theory and QED is a quantized field theory. But when you go out to a higher precision in QED then virtual particles, Feynman's diagrams and orders of perturbation enter.

Like your analogy says - Particles have rules and will go off on their own but virtual particles are more like disturbances that will fade away with distance.


There is disagreement in the ranks also. The field is real, the virtual particles are not real, the field is not real but the virtual particles are. Once people get their degrees and begin research and teaching they absolutely do not all agree on these points.
On youtube you can watch many debates from the World Science Festival where top Physicists in similar fields can't agree on anything.

This is such a great thread. Thanks to all those who are posting here.

Theory of Gravity, three views:

This is the relativistic version of the theory of gravitational attraction:

i.livescience.com...

"The right-hand side of this equation describes the energy contents of our universe (including the 'dark energy' that propels the current cosmic acceleration)," Livio explained. "The left-hand side describes the geometry of space-time. The equality reflects the fact that in Einstein's general relativity, mass and energy determine the geometry, and concomitantly the curvature, which is a manifestation of what we call gravity.

We have three basic branches (classical/Newtonian, Einstein's equation, and advanced theories Minkowski, and others)

Einstein's equation, which is enhanced to give the full equation at the beginning of the post

G = 8πgT/c^4

Newton's F (force) = G * [(m1*m2)/r^2]

This wiki explains the terms. Anyone have anything to add?

R_[mu nu ]-[1 over 2]R,g_[mu nu ]+Lambda g_[mu nu ]=[8pi G over c^[4]]T_[mu nu ]

en.wikipedia.org...

=======
where R_[mu nu ], is the Ricci curvature tensor,
R, is the scalar curvature, g_[mu nu ], is the metric tensor,
Lambda , is the cosmological constant,
G, is Newton's gravitational constant,
c, is the speed of light in vacuum, and
T_[mu nu ], is the stress–energy tensor.

This paper gives a restatement of Newtonian gravity:

ned.ipac.caltech.edu...

In alternative language, newtonian gravitational theory states that the acceleration a (the rate of change of the velocity v) imparted by gravitation on a test particle is determined by the gravitational potential phi,

a = -dv / dt = -delphi,

and the potential is determined by the surrounding mass distribution rho by Poisson's partial differential equation

del·delphi = 4piGrho.

What I'm getting the sense of is that a field is something that exhibits a 'particle duality' when you shake the field, and the waves or excitations cause the particle/wave, or particle/field.

So you have a charge surrounded by something (a field) and when you shake that field around the charge, it causes ripples and the ripple gives off something, like a photon.

When you make that analogous to the Higgs Field, you shake the Higgs field and it has an excitement, but it's a denser strata, and that causes a local excitation which results in a Higgs Particle.

I'm supposing that due to symmetry you can have a negative Higgs Particle?

Now, the Higgs loves to interact with itself the most strongly. It will be interesting to see if, when it is fitted into the Standard Model if it still doesn't quite fit, IOW still has some symmetry breaking.

I've just had a little ah-HA! moment wrt to symmetry breaking, i.e. the breaking of gauge symmetry (the W+, W- and Z bosons being large masses), that lead to the postulation of the Higgs particle. That finally made a bit of sense.

I didn't -quite- get the importance of symmetry-breaking, until watching some of the Great Courses lectures, (Sean Carroll and Stephen Pollock).

a reply to: FriedBabelBroccoli
Here are some things to consider:
The official name is SLAC National Accelerator Laboratory but if you spell out what SLAC originally meant, you get
"Stanford Linear Accelerator Center National Accelerator Laboratory", so with "accelerator" or an acronym for it appearing in the name twice, you can be sure that running their huge accelerator is their core project. They might have some other projects too which is why I asked if you might have run across something else they were working on and I don't know much about that.

So once you know it's an accelerator, what do you know about what accelerators accelerate? Well, they can't accelerate light, because the speed of light is constant. So, it must be something else like particles, and it's hard to accelerate neutrons in an accelerator, so it would have to be charged particles.

In order to accelerate particles close to the speed of light, you can't have them bumping into air or other molecules, so you evacuate the air and create a pretty good vacuum so the charged particles can accelerate unimpeded.

So they are accelerating in this case electrons as the charged particles, but let's take your explanation for a moment and presume they send light down the vacuum tube into the undulators. Since there's no medium, the light isn't subject to the Faraday effect and it would pass through the magnets without being affected by them, so the magnets wouldn't do anything to light even if they were sending light instead of electrons down the apparatus.

If you're using magnets to polarize light it must be passing through some kind of medium instead of a vacuum like at the SLAC. At the SLAC the electrons are the key as the undulator magnets do affect those, and the X-rays and the electrons actually interact with each other in the undulators. If you get a chance to watch the video it's worth the time to watch it, as it's one of the better animations I've seen, of anything.

originally posted by: Maverick7
I'm supposing that due to symmetry you can have a negative Higgs Particle?

Are you talking about the antiparticle of the Higgs? It's thought to be its own anti-particle like the photon and gluon. Some extended versions of the standard model predict more than one Higgs boson but we won't know if those models are right unless more Higgs bosons are discovered. I don't know much about those models but I would have guessed that the other Higgs bosons would also be presumed to be their own antiparticles, though I'm not really sure about that.

So you are interested in gravity. read thru my thread in my signature to get an alternate view to Einstein
a reply to: Maverick7

originally posted by: Maverick7
This is such a great thread. Thanks to all those who are posting here.

Theory of Gravity, three views:

This is the relativistic version of the theory of gravitational attraction:

i.livescience.com...

"The right-hand side of this equation describes the energy contents of our universe (including the 'dark energy' that propels the current cosmic acceleration)," Livio explained. "The left-hand side describes the geometry of space-time. The equality reflects the fact that in Einstein's general relativity, mass and energy determine the geometry, and concomitantly the curvature, which is a manifestation of what we call gravity.

We have three basic branches (classical/Newtonian, Einstein's equation, and advanced theories Minkowski, and others)

Einstein's equation, which is enhanced to give the full equation at the beginning of the post

G = 8πgT/c^4

Newton's F (force) = G * [(m1*m2)/r^2]

This wiki explains the terms. Anyone have anything to add?

R_[mu nu ]-[1 over 2]R,g_[mu nu ]+Lambda g_[mu nu ]=[8pi G over c^[4]]T_[mu nu ]

en.wikipedia.org...

=======
where R_[mu nu ], is the Ricci curvature tensor,
R, is the scalar curvature, g_[mu nu ], is the metric tensor,
Lambda , is the cosmological constant,
G, is Newton's gravitational constant,
c, is the speed of light in vacuum, and
T_[mu nu ], is the stress–energy tensor.

Minkowski is more related to space-time and Special Relativity. There is a field theory of gravity that uses Minkowski space-time and it's actually pretty old. But it ends up with the same results as GR.

There is Loop quantum gravity also and then string theory supposedly has a model of gravity.
And of course Bob Lazar.

a reply to: joelr

I found a description here which I really like:

profmattstrassler.com...

The best way to approach this concept, I believe, is to forget you ever saw the word “particle” in the term. A virtual particle is not a particle at all. It refers precisely to a disturbance in a field that is not a particle. A particle is a nice, regular ripple in a field, one that can travel smoothly and effortlessly through space, like a clear tone of a bell moving through the air. A “virtual particle”, generally, is a disturbance in a field that will never be found on its own, but instead is something that is caused by the presence of other particles, often of other fields.

Analogy time (and a very close one mathematically); think about a child’s swing. If you give it a shove and let it go, it will swing back and forth with a time period that is always the same, no matter how hard was the initial shove you gave it. This is the natural motion of the swing. Now compare that regular, smooth, constant back-and-forth motion to what would happen if you started giving the swing a shove many times during each of its back and forth swings. Well, the swing would start jiggling around all over the place, in a very unnatural motion, and it would not swing smoothly at all. The poor child on the swing would be furious at you, as you’d be making his or her ride very uncomfortable. This unpleasant jiggling motion — this disturbance of the swing — is different from the swing’s natural and preferred back-and-forth regular motion just as a “virtual particle” disturbance is different from a real particle. If something makes a real particle, that particle can go off on its own across space. If something makes a disturbance, that disturbance will die away, or break apart, once its cause is gone. So it’s not like a particle at all, and I wish we didn’t call it that.

The "virtual particles" are considered a bad name, I'd call them virtual non-particles They often represent 'polarizations' or interactions.

Quoth Matt:

Students of math and physics will recognize real photons as solutions of a wave equation, and virtual photons as related to the Green function associated with this equation.

The Green's functions are used to compute the effect of interactions.

On virtual particles, they are more concepts used to carry properties during interactions but are not direct observables.

Think of them as the items that perform the interaction, they are required to follow certain rules and have certain properties depending upon what type of virtual particle it is. It is a weird concept I agree.

The whole thing about maxwell and moving then onto perturbations and loop corrections is simply a matter of asking the question what if?

Many people think that the models we have are very rigid, cold and do not represent anything in nature, but, think about the following example...

You fire a tennis ball from a calibrated catapult. The air is still (as far as you can tell) but still the ball lands in different spots each time. If the catapult does give you EXACTLY the same energy each time, then what causes those differences? Well, maybe the air isn't as still as you think, maybe the temperature along the flight path is different each time. These are all concepts we can understand and think.. well what if? We could apply each of those concepts knowing enough about fluid dynamics to figure out exactly the range in which the ball will land given the circumstances.

Now... apply this to something like, a radioactive decay, or a interaction cross section... a more alien concept.

We have a model that has a set of rules, things that can happen and things that cannot.

Well if an interaction can happen, then what stops it happening all the time? why does firing an electron with an energy of say 40eV at an argon atom not always result in double ionized argon? Why do unstable isotopes not just decay instantly?

Well, this all boils down to our rules and the same question... what if?

Lets say you have a particle X and as it propagates it will turn into particle Y easy calculation? On the surface yes! but your calculation (based on inputs from other interactions you have observed) only gives you about 10% accuracy on the rate of decay or transmutation from X into Y... BUT your theory says that X can undergo an interaction that puts it into an intermediate state, but is otherwise unchanged physically... so why not?

So you then do a calculation that asks, what is the rate of change from X into Y with this interaction that i know occurs at a set probability or rate... Your calculation gives you 5% accuracy! great, you think harder and realise, hmmm wait it is possible to have many many many of these intermediate events occuring, so what does this do to my rate calculation... and boom... what you have is a loop correction and it doesn't usually give you infinite accuracy, but it allows you to more closely predict reality.

that might have been the most confusing and crappy explanation ever, but iv been up since 4:40 to get underground to continue building that Dark Matter experiment I work on... haha... finishing touches... it is so damn close!

a reply to: ErosA433

Why do you think it is possible for an earth based experiment to detect dark matter?

Is it theorized that it is hypothetically possible to detect dark matter itself, or is the experiment an attempt to detect other things, and claim that those other things that were detected are results of interacting with dark matter?

Is it possible dark matter is similar to a virtual particle concept?

originally posted by: ImaFungi
a reply to: ErosA433

Why do you think it is possible for an earth based experiment to detect dark matter?

Eros already said it might be possible or it might not be possible for Earth based or any other experiment to detect dark matter directly. Neutrinos are already hard to detect because so few of them interact with detectors, so if dark matter particles interact even less, then the only evidence we might have of them is their gravitational interaction. The distribution of dark matter is a mystery to me though. It seems to comprise maybe 85% of the matter in the universe but very little of it appears to be in our solar system. Even if most of it is in what they call "halos", I would imagine a few particles still might make it to underground labs in Earth but I have no idea how many.

Is it theorized that it is hypothetically possible to detect dark matter itself, or is the experiment an attempt to detect other things, and claim that those other things that were detected are results of interacting with dark matter?

I suggest reading his excellent thread:

Direct Dark Matter Detection [A review]

Note the word "direct".

just build an over unity machine (many are there on the internet)and you will get electrons out of the time domain, which are the dark matter
dark matter search ends here
a reply to: ImaFungi

originally posted by: Nochzwei
just build an over unity machine (many are there on the internet)and you will get electrons out of the time domain, which are the dark matter
dark matter search ends here
a reply to: ImaFungi

You do not seem to understand that you do not understand that you are making statements that you do not understand and you do not understand that you do not understand how they are wrong.

a reply to: Arbitrageur

If no dark matter is directly or indirectly detected, would the experiment be a waste of money, resources and time?

Would your answer differ, if the reason no dark matter would be detected is due to hair brained theory?

originally posted by: ImaFungi

originally posted by: Nochzwei
just build an over unity machine (many are there on the internet)and you will get electrons out of the time domain, which are the dark matter
dark matter search ends here
a reply to: ImaFungi

You do not seem to understand that you do not understand that you are making statements that you do not understand and you do not understand that you do not understand how they are wrong.

Lol how clownish of you.

a reply to: ImaFungi
If the experiment that should have detected something, does not detect anything, we have gained knowledge that the experiment is based on an incorrect hypothesis.

The negative result is sometimes even more informative than the positive.

Moreover, a negative result is the clue that effort should be taken to some other direction.

A positive result that confirms what we "knew" all along adds no information.

originally posted by: ImaFungi
a reply to: Arbitrageur

If no dark matter is directly or indirectly detected, would the experiment be a waste of money, resources and time?

Would your answer differ, if the reason no dark matter would be detected is due to hair brained theory?

Actually, proving that dark matter either does not exist at all or is way different than what we thought and thus was not detected would be a spectacular feather in someone's hat. Possibly Nobel quality.

a reply to: Bedlam

Even if it was possible to do that by thoroughly critiquing current theory and observation? Without the need for multi billion dollar dust collector?

a reply to: Bedlam

Dark matter/evidence will not be detected on/under Earth; and if 'it is' then those who say 'it is' are lying to themselves and others whether they know it or not. The problem is with theory.

originally posted by: ImaFungi
a reply to: Bedlam

Even if it was possible to do that by thoroughly critiquing current theory and observation? Without the need for multi billion dollar dust collector?

You mean like when Marko Rodin announced 5 years ago what dark matter really was?

RodinAerodynamics

And the 9 demonstrates the omni dimension which is the higher dimensional flux emanation called Spirit that always occurs within the center of the magnetic field lines. The last number left to be explained from The MATHEMATICAL FINGER PRINT OF GOD is the number 9. The number nine is Energy being manifested in a single moment event of occurrence in our physical world of creation. It is unique because it is the focal center by being the only number identifying with the vertical upright axis. It is the singularity or the Primal Point of Unity. The number nine never changes and is linear. For example all multiples of 9 equal 9. 9x1=9, 9x2=18, but 1+8=9, 9x3=27, but 2+7=9. This is because it is emanating in a straight line from the center of mass out of the nucleus of every atom, and from out of the singularity of a black hole. It is complete, revealing perfection, and has no parity because it always equals itself. The number nine is the missing particle in the universe known as Dark Matter.

So you gotta wonder why we are still looking for dark matter when he already told us what it was, and you probably have an equally compelling explanation as does Nochzwei with his "electrons out of time domain".

Lots of people make lots of claims and critiques but Nochzwei, Marko Rodin and probably you too lack proof to back up such claims.

While Moffat does provide some evidence for his claim that dark matter isn't needed to explain galaxy rotation curves, scientists who have offered an opinion seem to think his modified gravity model can't account for bullet cluster observations.