Bobort
Positrons as electrons moving back in time is not forbidden by the model we use to explain particle behavior. Thus, it is as accurate to say that that is what happens as it is to say that the positron is a seperate particle. Either expression can be accurate.
Spiritus Noooo! Not another model debate! 
I’m outa here!..
I am irresistibly reminded of the old joke where a man calls up the patent office and asks for a list of everything that hasn’t been invented yet. ‘Cause, "Ya see I’m a thinkin’ of doin’ some inventin’ and don’t want to waste m’ time."
In a like vein the poster would like a list of everything we don’t know yet.
Myrr21 wrote:
Mathematically speaking, a “field” is a function that takes as its argument(s) a position in space and yields one and only one numeric value, either scalar or vector, for that point in space. Fields are useful for modeling some real-life regions of space: one can say there is a “temperature field” in a room, where each point within the room has a temperature.
The field Faraday was talking about was an electromagnetic field. Mathematically, this is just a vector-valued function that yields one “field strength and direction” for every point within the region you’re scrutinizing. The field strength vector for a given point defines how a charged (or magnetically polarized) particle within the region will respond.
The question I think you’re really asking is “what causes an elecrtromagnetic field?” The answer is, as Feynmann, Gauge, et al. discovered in their work on Quantum Electrodynamics, that charged particles exchange virtual photons between each other. Virtual photons, just like real photons, have a tiny amount of momentum. These virtual photons thus “push” on each charged particle. The overall effect is what we call an electromagnetic field.
Thanks! That was the story I was looking for.
This quote does sort of sum up my position:
Hopefully, this will further the understanding of quantum gravity, in any event.
Well put, but I think you missed my point. I am aware of what a field is mathematically speaking. My point is that it’s fundamentally a kinda silly–albeit very usefull–model…and just a model. Our whole understanding of all the basic laws of our universe is based on models that have proved useful, but could easily be revised in the face of new evidence.
(side note: while Faraday was only referring to the EM field, he defined it as a condition of space, not a function, and the idea was basically yoinked for other fields just because it was useful)
Well put, but I think you missed my point. I am aware of what a field is mathematically speaking. My point is that it’s fundamentally a kinda silly–albeit very usefull–model…and just a model. Our whole understanding of all the basic laws of our universe is based on models that have proved useful, but could easily be revised in the face of new evidence.
(side note: while Faraday was only referring to the EM field, he defined it as a condition of space, not a function, and the idea was basically yoinked for other fields just because it was useful)
Good bye.
There is no center of the universe, or the center of the universe is everywhere. A 2D-3D analog is the classic inflating balloon. The surface of the balloon (2D) is embedded in higher dimensions. As the balloon inflates, everything gets further away from everything else, yet there is no center. Reverse the process and the spherical surface collapses to a point, where everything was in the same place at once.
Sigh. I’m obviously not being clear enough in my explanation. Imagine the expanding balloon again. Now take a snapshot of the expanding balloon at some point (like a singal frame from a movie). In the context of the snapshot the balloon isn’t expanding (that’s why it’s a snapshot). On the surface of the balloon, a line can be drawn from a point which returns to the same point, even though it’s on a “straight line” on the sphere. The curve is embedded in the higher dimension. By the same token, one model of a closed universe is one that has a finite volume, but no boundary (as attributed to Einstein in the Britannica article you referenced). I was not suggesting actually moving through space, but rather casting a ray in the model. It was an attempt to describe the model, not describe an experiment.
Um, no. There is apparantly a repulsive force pushing stuff apart. The model for that is so-called “exotic” matter, etc. It has no place in our concept of gravity. And though there is theory, it hasn’t been confirmed. (Also, I can’t access the yahoo link because it has expired.) I think it’s odd to say that we had it right all along when it was such an unexpected find.
Why? I fail to understand why consciousness must be some external factor. Consciousness seems like some abstract philisophical thing like sight. We see it, but it doesnt mean that is what it is in reality.
I always just thought consciousness was just a “by product” of thinking. The same processes that allow us to remember and rationalize (Neurons in the brain firing in patterns I suppose) also allow us consciousness.
AFAIK we have seen absolutely no evidence for spirit or soul. Is this statement saying that it is something that cannot be detected in anyway? If so, wouldn’t it be safe to say that if it cannot be detected, proven or no evidence can be found, then it is nothing more than a philosophical thought?
Here is the same story from Space.com, which is a GREAT website, BTW.
Spiritus, you are correct if you restrict yourself to QED and QCD interactions because all such interactions are symmetric under both charge conjugation © and time-reversal (T). So it is possible to redefine the time-reversal operator to include charge conjugation–this leads to the interpretation that an antiparticle is a particle travelling backwards through time.
Unfortunately, the weak interactions aren’t so nice. The problem is that there are weak interactions that violate C symmetry but still respect T symmetry. The classic example is the neutrino. All neutrinos are “left-handed” and all anti-neutrinos are “right-handed”. Nevermind what left- and right-handedness means for now; the important thing is that handedness doesn’t change under either charge conjugation or time reversal. C symmetry is obviously violated: C takes a left-handed neutrino to a left-handed anti-neutrino, and there is no such thing. T symmetry is fine, though. Under T, the left-handed neutrino remains a left-handed neutrino. However, if we interpret T to include C–i.e. if we say that a particle travelling backwards through time is its own antiparticle–we end up with a left-handed anti-neutrino again. An anti-neutrino cannot be a neutrino moving backwards through time, so it doesn’t really make sense to use that interpretation anymore.
Ahh, before somebody points it out to me, I see the "what is concsiousness thread, I’ll read it now.
slinks off
Too bad I did’nt see it before I opened my yap in this thread. Therefore making myself look stupid.
Yes, but by the same token it makes no sense to speak of charge conjugation for neutrinos at all. I must admit, I have never been strong on neutrinos. Little buggers have no sense of propriety at all. What is your interpretation of the failure of C over neutrinos? For that matter, what ramifications does the case of neutrinos have for other T-C correspondences?
The charge conjugation operator is poorly named. It doesn’t really have anything to do with charge except insofar as charged (anti)particles flip sign under it. By definition it takes particles into antiparticles. As another example, gluons have no charge but they change color under C.
You’re right, though, neutrinos are obnoxious. Recent data suggests they might be violating conservation of lepton number also. I think they’re just doing it for attention.
C violation is weird, but it (actually CP violation) is probably responsible for the fact that there’s hardly any antimatter in the universe.
You might wonder whether you could just change the definition of C for neutrinos and keep the antiparticles-go-backwards interpretation. It would be kind of ugly but theoretically sound. Unfortunately there are analogous symmetry violations for hadronic weak interactions. Hadrons are all charged (or rather are made up of charged quarks), so you can’t make an exception for them without breaking everything for QED and QCD.
I was aware of CP assymetry and the proposal that it acounted for the assymetry of matter/antimatter after the Big Bang, but I had never thought to wonder what ramifications that had for broader CPT parity issues. I’ve been trying to find some recent papers on the web, but keep running into restricted archives.
I did find this report on a CPLEAR experiment that seems to confirm T-assymetry for K mesons, too (what’s up with those K mesons? No parity is good enough for them?). That seems to mean that neither C, P nor T is symmetric, CP jointly is assymetric, but CPT together holds. (Aside: has this experiment been reproduced? I saw several mentions, but they all seemed to point to the single result.)
I saw mentions of a couple of opposing theories about CP violation (superweak force or Kobayashi-Maskawa). Do you know if they extend to this quantum-scale violation of T reversal? Also, does the standard model demand that gravitons also show T assymetry, since black holes violate T reversal at the (very) macro scale?
Finally, since your reading seems much more current than mine, do you know of any experimental tests to distinguish between the superweak and Kobayashi-Maskawa models? From the little bit I could find on the web I lean toward K-M. It isn’t as “elegant”, but I don’t know that I feel good postulating a new fundamental force observable only in K-mesons and dipole moments.
Interesting. I wasn’t aware that someone had confirmed T violation for the Kaons. Thank god for that. If combined CPT symmetry is violated anywhere then modern theoretical physics basically gets knocked on its ass. So those Kaons had better damn well be violating T.
Previously CPT symmetry was inferred in this case because there isn’t any detectable difference in mass between the K[sup]0[/sup] and the anti-K[sup]0[/sup].
I think most of the work being done these days on CP-violation is trying to find it happening somewhere other than the neutral Kaons. These guys are looking for it in the B mesons.
Sorry, I don’t know anything about the superweak force. How long ago did you hear about it? I looked through the most recent particle data booklet and couldn’t find anything about superweak theory. However there’s quite a bit of discussion about the phase factor in the K-M matrix to accommodate CP violation.
As for T symmetry violation, as far as I can tell the most interest in it has to do with CP violation and making sure CPT holds. I think one reason for this is that it’s not easy to find T violation in the lab.
The standard model doesn’t have much at all to say about gravitons yet. Even though a lot theoretical of work is being done on quantum gravity, and experiments like LIGO are now looking for gravitational waves, most people I’ve talked to (who know what they’re talking about) think that detection of gravitons is several decades or even a century away. I think it’s way too early to make any serious predictions about stuff like whether or how T violations occur (there’s my non-hijack contribution to the thread).
OK, let’s try again
First, let me correct several misunderstandings in your reply:
Now, in my reply I listed one theoretical problem (quantum gravity) and four observational/experimental problems. Your answer assumes that solving the first will solve all the others. This may or may not be true. For instance, we could come up with a perfectly good theory of quantum gravity that says nothing about particle interactions (other than, presumably, gravitons), just like QED is a quantum theory of electrons and photons that says nothing about quarks. So a solution to quantum gravity might solve all or none of the observational difficulties. Obviously, a “theory of everything”, if it existed, would (by definition) solve all of the above-mentioned problems, but, since there is as yet no experimental confirmation of string theory, we don’t have a TOE right now. If you’re going to lump every outstanding problem into one box, then what your OP is really saying is “science has solved everything except the stuff it hasn’t solved”, which is of course true but trivial and uninteresting.
To go back to the OP:
This is simply untrue as in the examples I cited previously.
There’s also no particular reason to believe any of the existing theories will be proven valid. However, even if the claim you are making is “we have theories that might explain everything”, I disagree. String theory (the only candidate for TOE I’m aware of) is itself not well understood. Even if experimental evidence for it is found tomorrow, there will be many things that need to be checked, both experimentally and theoretically, before string theory can be claimed as “knowledge”.
Spiritus Mundi wrote:
That’s 'cause neutrinos are only created by the weak force! Hah! Get it? <rimshot> I’ll be here all week, tip your waitstaff!