Reaching the practical end of physics?

Hi, H.Sorry that I haven't been participating in a few of your other threads. Been real busy to write long posts, and those threads were getting wacky anyway.But as far as this point:I will point out that to the best of my understanding, useful devices like NMR and PET scans were developed after through the investigation of the properites of atomic nuclei and their constituents. What is interesting is that these imaging techniques don't really rely on using the protons and neutrons as individual particles -- rather they rely on the understanding we gained as protons and neutrons were studied as individual particles and how they behave when combined in nuclei.In a similar vein, in investigating the quantum mechanical nature of electrons, especially their behavior in solid matter, I don't think the physicists of the early 20th century could have realized that the electrical devices with which they were familiar would be completely replace in many applications (and totally new applications developed) by the then unknown properties of semiconductors.So it may very well be that stuff like quarks and vector bosons will themselves will not be of direct practical importance. But understanding them may lead us to new understandings of the nature of mundane, bulk matter that will have practical applications.Pretty much hard to say.And, as I've said before, I think that primary value of this type of research lies more in the "Gee whiz!" factor more than in any real "practical" applications that may come out of it. But then, my main training has been in mathematics which in the main part is conducted with very little thought of "practical importance", at least by the participants themselves, so I have a fondness for learning and intellectual achievement for its own sake.-Now as far as "the end of new physics is concerned", we aren't in the same position as the scientists of the turn of the 20th century. (Or is 1900-01 the turn of the 19th century?) I don't think anyone is naive to believe that we are close to knowing everything, and that all that will be left to do is to dot the i's and cross the t's.Rather, if there is a problem, it's with the availability of energy. Now to study ever smaller scales requires ever greater energies at which to "smash those atoms". And, although I don't think that we are at that point yet, there is only so much energy that will be available to us whatever our level of technology -- unless we discover something that will allow us to get around the laws of thermodynamics. So it is possible that someday in the far future we will hit a wall simply because the fundamental laws of nature itself will not allow us to probe any deeper. Or, as another possibility, our understanding of physics changes and we realize that we don't need higher energies to probe deeper into the fundamental nature of the universe.

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Progress in human affairs has come mainly through the bold readiness of human beings not to confine themselves to seeking piecemeal improvements in the way things are done, but to present fundamental challenges in the name of reason to the current way of doing things and to the avowed or hidden assumptions on which it rests. -- E. H. Carr

Well, my point is that the initial investigations did use pretty high energies and exotic energy sources. I believe, in fact, that some of the earliest experiments were conducted at high altitudes because at the time cosmic rays were the highest easily available energies. Then, as particle accelerators became common, the scientific investigations involved accelerating the nuclei to incredibly high energies.Now, to conduct NMR the just put the patient in these huge magnets. And PET simply relies on radioactive isotopes to produce their own positrons. So the knowledge was gained from bulky apparatuses (apparati?) and very high energies, but is implemented using much more manageable equipment and much lower energies.Similarly, we may be using very high enegies to study such very ephemeral phenomena, but that may give us knowledge about the behavior of even ordinary matter that will allow us to manipulate it at more reasonable energies.I agree that this is kind of a stretch. I, myself, don't expect much practical used to come out of this. But what do I know? Twenty years ago I was the guy who insisted that the dinosaurs could not have been wiped out by a meteor.

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Progress in human affairs has come mainly through the bold readiness of human beings not to confine themselves to seeking piecemeal improvements in the way things are done, but to present fundamental challenges in the name of reason to the current way of doing things and to the avowed or hidden assumptions on which it rests. -- E. H. Carr

It's even worse than you think. "Go back in time to the same position in space" is meaningless -- there is no absolute determination of position. Position depends on the frame of reference; of course, there is no absolute measurement of time, either, so one couldn't really say "go back in time 5 minutes" either. Five minutes in which frame of reference? To go back in time, one would have to specify both time and spatial coordinates relative to a particular frame of reference.On a related note, the science fiction author Larry Niven (at least I think it was Niven) had an interesting point when he wrote stories that involved teleportation. If one teleportation station is at a different altitude relative to another, there is a change of potential energy in the teleported object (or person) that had to be taken care of somehow; for example, if an object was teleported to a lower altitude, the potential energy would be converted to heat, which would heat the object if it wasn't somehow dumped somewhere. As I recall, in one story this adjustment wasn't perfect, and a murderer tried to hide the time of death of the victim by teleporting the corpse to a lower altitude, using the heating to throw off estimates of the time of death. Niven also mentioned problems with adjusting kinetic energy and momentum if the two stations are moving relative to one another.Anyway, think of the massive heating problems Capt. Kirk faces teleports to the surface of a planet from an orbiting star ship!

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Progress in human affairs has come mainly through the bold readiness of human beings not to confine themselves to seeking piecemeal improvements in the way things are done, but to present fundamental challenges in the name of reason to the current way of doing things and to the avowed or hidden assumptions on which it rests. -- E. H. Carr