Oh come on! Surely you know that gamma-gamma pair production is merely annihilation in reverse. Surely you know about the Breit Wheeler process: "The process was described by Gregory Breit and John A. Wheeler in 1934 in Physical Review.[3] Although the process is one of the manifestations of the mass–energy equivalence, as of 2014, it has never been observed in practice because of the difficulty in preparing colliding gamma ray beams. However, in 1997, researchers at the Stanford Linear Accelerator Centre were able to conduct the so-called multi-photon Breit–Wheeler process using electrons to first create high-energy photons, which then underwent multiple collisions to produce electrons and positrons, all within same chamber.[4] In 2014 a model of a photon–photon collider was proposed, where Monte Carlo simulations suggest that it is capable of producing of the order of 105 Breit–Wheeler pairs in a single shot.[1]" Besides, in pair production using a nucleus, the incident photon is converted into an electron and positron, and the nucleus is still there. So we can make matter from light. Why are you trying to dismiss and deny accepted science in order to make a point? There's a pattern here, isn't there? I tell you some physics or what Einstein said, and when it doesn't fit with your popscience pseudoscience misunderstanding, you dismiss it. See above, check out SLAC, and have a read of the Wikipedia two-photon physics article: "Two-photon physics, also called gamma–gamma physics, is a branch of particle physics that describes the interactions between two photons. If the energy at the center of mass of the system of the two photons is large enough, matter can be created.[1]" No, I tell you about physics, and I back it up with references. When it doesn't match your popscience understanding, you dismiss it.
Being subject to Newton's laws of gravity is not General Relativity. Hence, "Prof. Barbour's" example fails. :EDIT: And he's not even a professor. But he wrote cranky books and papers before I was born. Good for him!
Good stuff tashja. Let's have a look at what Julian Barbour says: If nothing changes, one cannot speak about time. Thus, change is primary. Moreover, one can formulate laws of change without the notion of time as something which exists in addition to the things that change. Take a simple example: three particles that move subject to Newton's law of gravity. At any instant they form a triangle. Its size and shape change continuously. Because the change is continuous, you can lay all the successive triangles out in a line and call it a timeline. However, there is no line (and hence no time) without the triangles. It is the triangles and the law that governs their change which creates what you call time. The components (things and law of change) together also enable one to speak of duration, but it does not exist without the two primary components. Sounds good to me. And very different to the message in his 1999 book The End of Time. There he advocated a block universe where motion is an illusion. Google on Barbour motion is an illusion. For more on duration, see my essay The Nature of Time on my website. In short, one can show that one does not need time as a primary notion. It's a bit like names that one gives to people. In the first place they are distinguished by their DNA and many other features. A name is something we add for convenience. Best wishes, Julian Barbour. http://www.platonia.com/ Again, sounds good. But again, when you read The Nature of Time, you see things like this on page2: "The one I favour seems initially impossible: the quantum universe is static. Nothing happens; there is being but no becoming, the flow of time and motion are illusions." But to be fair to the guy, he isn't saying that in this essay, instead he's saying things like this: "I shall show that intervals of time do not pre-exist but are created by what the universe does. Indeed, Newton can be hoist by his own petard if we see what his marvelous laws actually tell us." This fits in well with what I and others have been saying. See for example "Mach in contrast was right, we do abstract time from motion". But then he goes and says this: "We shall see that this leads to a very different definition of clocks - and understanding of time - to that of Einstein, given below." It's as if he's never read Palle Yourgrau's 2005 book A World without Time: the forgotten Legacy of Gödel and Einstein. And a quick look at his papers on arXiv suggest to me that he doesn't really believe in his own essay. If he did, IMHO we'd be seeing papers on the variable speed of light and how gravity actually works. Not papers on a gravitational arrow of time.
Good stuff river. It's a shame the diehards won't face up to it. But then as Max Planck said, science advances one death at a time. I tell you, if we hadn't had a Max Planck, Einstein would have stayed a patent clerk.
Barbour is probably a crank, outside academia and has been at this for longer than you, Farsight, so where is his Nobel Prize? Hasn't it ever occurred to you that elementary school children could come up with the same ideas that you and your ilk have? :EDIT: I wonder how his PI seminar was received. That special place between UW and the liquor store doesn't seem so special anymore.
That's it? In that proces the photons in the photon-photon interaction, we're not observed. They were implied as intermediate steps in a theoretical interaction. No one has yet proven gamma gamma interactions as anything more than an explanation, for results they observer... Even then they rely on interpretation based on the underlying theory. I am not saying it does not or cannot happen, just that the gamma gamma interaction resulting in electron/positron production has not been directly observed.... Observing a gamma ray is a destructive process. Once you can say with certainty it is there it can no longer interact with anything else let alone another gamma ray. Farsight, it is one thing to accept a theory as valid, even a valid explanation for an observable event, a completely different thing to have directly observed the theoretical component. You continue to confuse the theoretical explanation with the physically observed results.
I'm not confusing anything. Now pay attention: In 1997, researchers at the Stanford Linear Accelerator Centre were able to conduct the so-called multi-photon Breit–Wheeler process using electrons to first create high-energy photons, which then underwent multiple collisions to produce electrons and positrons, all within same chamber
Eh, I can't find 1997 on that page. Neither can I find a reference to Breit–Wheeler. So I reported your post for false information.
Now pay attention to the portion in bold! While it is true that you could detect high-energy photons emerging from the initial collision, any high-energy photon that was detected could not be observed as a component of the interaction leading to electrons and positrons, in the same chamber. Photons to do not leave tracks. The detection process is destructive. What you point to as proof is electron collisions that result in electron/positron production which theoretically involves high-energy photons as an intermediate stage. Pay attention, Farsight.., the fact that theory supports the chain of events is not the same as proof. What I asked for was some reference that did not involve an initial massive particle collision........ Do you really believe that the high-energy photon-photon interaction was observed? Or is it more like, what they observed fit with the end results of a theoretical process. You really do have some difficulty understanding the difference between theory and.... But you do have an active if not accurate imagination.
Phooey. You said this: "Theoretically two high energy gamma rays could interact directly with each other, resulting in a positron/electron.., but that.., so far remains theory." And I quoted the above, which included this: "high-energy photons, which then underwent multiple collisions to produce electrons and positrons". Bah, naysayer. You're just another of those guys whose doesn't know any physics, and never will. Because when I give the references and evidence to back up what I'm saying, you dismiss it all. Now, can we get back on topic please?
And how did they, the physicists involved, determine that the produced positrons and electrons, were the result of high-energy photon collisions? HINT as an interpretation of results based on a theorized process. What happened was there was an electron initiated collision that resulted in both electrons and positrons, through a process which is theoretically explained as involving an intermediate photon-photon collision stage. Your same initial quoted reference includes the following.., NOW PAY ATTENTION! Never been observed, as of 2014 and a 2014 proposed, but not built.., photon-photon collider.., which mich be used to prove the underlying theoretical process. You need to pay attention to the whole of even your own references. Photon-photon collisions of any character remain theoretical. They have not yet been directly created or observed... Again Farsight, do you understand the difference between what remains theory and what has been proven? I'm not asking what you imagine to be real or believe, just what is real.., as in.., has been proven.
OK, I found the reference. Albeit buried. The process was described by Gregory Breit and John A. Wheeler in 1934 in Physical Review.[3] Although the process is one of the manifestations of the mass–energy equivalence, as of 2014, it has never been observed in practice because of the difficulty in preparing colliding gamma ray beams. http://en.wikipedia.org/wiki/Breit–Wheeler_process#cite_note-nature-1\ And by buried I mean when you copy/paste wiki all the links transfer as well. So I skimmed through all the links.
Here's the 1997 paper out of SLAC: http://www.hep.princeton.edu/~mcdonald/e144/burke_prl_79_1626_97.pdf
Here is a quote from the professor's "ideas" on time: "Mach remarked: “It is utterly beyond our power to measure the changes of things by time. Quite the contrary, time is an abstraction at which we arrive through the changes of things.” Thus, time as such does not exist but only change." It is true than without motions (which is the ONLY way we can & do measure time) time would not exist; but my POV is a little less firm as motion does exist, but there is zero need of any time concept to describe any and all motions (including chemical processes that are just atomic scale motions). It is Ockham's rule which allows me to say time does not exist. (Newton's version of that rule is a little more precise and limits it to the philosophy of reasoning - he had to "watch his step" - The church knew God's angels where keep the universe orderly. - Doubt that and you could burn, tied to a stake, before an eternity in hell.) Some have without proof or reason asserted the opposite" With out time, motion would not exist" as if time or some other agents (angels ?), were needed to push a falling rock toward the earth's center. Probably not strange he and I agree - He appears (in photo at his site) to be another "old nerd" with Ph.D. in physics, like me, retired from a university. I have not posted for some pages - the level of silly crap / opinions* is too high, but decide to endorse the professor's POV. * By edit: Trippy's link (post 796) NOT included, of course. It gives experimental evidence of high energy photon collisions making more than 100 electron/positron pairs. So I'm glad I do still wade thru (rapid skim) the crap to find a few gems. Quite clever of them to (Compton) back scatter a few photons off very high energy electron beam back into the on-coming laser beam. Much more** than twice the laser photon's momentum was transfer to the scattering electron, and as energy had to be conserved, a part of the electron's relativistic mass energy was given to the back scattered photon converting it into a gamma ray! ** "Much more" because the laser's photon's momentum was reverse and greatly increased to that of a gamma ray headed towards the laser. If I were not too lazy (and busy to read more than the abstract) I could apply Compton scatter equations and tell the energy gain of the reversed photon - the gamma ray. Again: very clever. These 100 or so, man-made, gamma rays may be the most harsh man has ever made. The gamma ray in the lab frame had probably more than the 1.22Mev required.
Say something is true because you feel like ignoring general relativity? Experimental evidence in high energy photon collisions that has never been observed? And you complain about "silly crap"? :EDIT: I may be at a miss on the high energy photon SLAC experiment, but Billy has posted so much nonsense already my initial reaction to them now is mostly disgust. And to busy to read everything right away.
Hehe.. Old school minds think alike, eh? And why not? You've done the miles. You've earned it Please Register or Log in to view the hidden image!
Thanks again tashja for the effort in asking these pertinent questions. On this one though, you have finally picked one whose thoughts I do disagree with. The statement from professor Barbour.... If nothing changes, one cannot speak about time. Thus, change is primary. Does not make much sense to me. I've stated many times that any change, or motion happens in time, and nothing as yet has changed that. The BB was not an evolution of change and motion.....it was an evolution of space and time, and change and motion occurred in that space and time, or spacetime. He then concludes with the statement....... In short, one can show that one does not need time as a primary notion. It's a bit like names that one gives to people. In the first place they are distinguished by their DNA and many other features. "A rose by any other name, etc ? Of course one needs time...especially if one accepts the BB and the evidence that supports it. If one decides to call time rose instead of time, then it still exists as rose, as it was what evolved from the BB. Having Professor Barbours opinion though, certainly supports my earlier claim which was agreed by Matt, that the debate on whether time is real or not is debatable simply because as yet we do not know the true nature of the beast. Irrespective, in my view, there is enough evidence to support that time is indeed real and that has been supported by other professionals such as Sagan, Thorne, Smolin, Carroll, Kaku, and Hawking. So what newbies to this forum must be aware of, is that the egotistical self gratuitous claims of Farsight and others are no more than opinions, and in Farsight's case, is just another example of the weird generally unsupported take he has on physics in general. That is obviously supported by another of tashja's replies from another professor, who advised Farsight to learn some GR. That statement is obviously true and should be heeded.
