A while back I got to wondering whether there is anything in the generally accepted physics that demonstrates that the laws of physics are applicable in the future. In the classes I’ve taken (pretty much restricted to standard mechanics and electromagnetism), it’s assumed that the fundamentals of physics - time, mass, energy, and the relationships between them - will be the same in the future as they are today. My question is whether that’s a grand assumption or something that is proveable.
It’s clear that as we learn more, new theories can be developed and verified through experiment, but ever since Newton, the basic mechanics that I deal with haven’t changed. I’m not asking about new theories, but whether the basics could someday change - the gravitational force goes away, etc. Is that impossible, or are we just ignoring that possibility?
It’s an assumption. It’s certainly an assumption that has been hotly discussed for decades, which means that it has been questioned by a few. There is no method of proof that anyone knows about, short of a complete understanding of all physical processes. This is still far beyond any current theories.
This is true but it is also subject to experimental testing. For example, by looking far distances, you are looking back in time due to the finite speed of light. There is some evidence that alpha, the fine structure constant is related to the electron charge, e; the speed of light, c; Planck constant, h; and epsilon the vacuum permittivity by
alpha = e^2/(2hc*epsilon)
It is a unitless quantity approximately equal to 1/137. It can be measured by looking at the spectrographic absorption lines. And as I said there is some evidence it may have changed. This would imply that one or more of the fundamental constants listed has changed over time.
There is also some theoretical work on a changing speed of light.
I don’t think it is fair to just say it’s assumption.
On one hand, it’s best to think of “laws” as ideas whose idea status has worn away. I imagine we all suppose there must be something about any given law that will be found wrong or improved upon in some way, and in a simple sense we’d expect any of the laws to turn out to be at least sort of wrong eventually.
On the other hand, these laws aren’t just islands independent of one another. In various ways they form structures that make sense. To the extent that we expect something that makes sense today will also make sense tomorrow, we expect some kind of continuity into the future. So, Galileo figured out a kind of relativity that still appears true enough that anybody working out the mechanics of moving bodies such as aircraft landing, guns recoiling, microphones flexing or bones breaking is going to take his relativity as perfect, and Einsteinian relativity is (except at really unusual velocities) a neglible tweak to that.
Now, there is another issue, whether constants such as the fine structure constant might be drifting a little over time, and it’s within the laws of physics already to think about the consequences of that, and an open question whether they do. I think you’d need something new, though, to explain WHY they drift.
It would be extraordinarily difficult to prove that the sun will rise tomorrow. I submit that the “laws of physics” should be held to an even higher standard.
What do you mean? The instant gravitational forces go away we all die, and the universe as we know it ceases to exist. How can you plan for that? What good would *not *ignoring that possibility do?
I took your original question to be a philosophical one. By definition, the laws of physics will always be true. We just have to figure out what they are.
OldGuy - thanks. I had not considered astronomical observations. If nothing else, that shows that the fundamentals have worked for a long time.
Contrapuntal - my question was more along the lines of whether things will work tomorrow like they do today. Thing seem to have worked the same way since people have been noticing, if you discount stories of interesting beings and events that we consider to be mythology these days. I realize that the physics of the Big Bang are consistent with how things work today, but was just wondering if there had been any proof that physics will work the same way tomorrow. I certainly count on it, but had never heard of anything that nailed it down.
sunacres - When you say that by definition, laws of physics will always be true, that confirms my (limited) understanding that we have decided that they will always be true. I realize that decision is based upon a lot of experience, but that doesn’t necessarily make it true for all time. I agree that my question is more philosophical than practical. First of all, I would have no idea how to respond if I even wanted to plan for changes in physical behavior. And second, I plan on going through the coming days without any worry that things might change. Just curious.
The problem is that almost nobody in the scientific community actually believes either of these things, which are among the issues I mentioned have been “questioned by a few.” And you wiki cite in fact gives no backing to the fine structure constant change findings. Just the opposite.
There is simply no good evidence, let alone proof, accepted by any more than a few physicists of any change in any constant.
Again, while all the evidence is that nothing fundamental has ever changed, this does not constitute a proof. First, we simply don’t have enough evidence of all behaviors through time. Second, we may not have detectors sensitive enough to recognize the rate of change. Third, the universe is comparatively young, and change may yet happen in the long term.
Without a fully realized and understood “theory of everything” in the most general sense, we have no firm idea of whether any change is possible or not. All our evidence currently tells us no, but it is strictly an assumption, albeit one based on very sound footing.
What I meant was that the laws will always be true, but our attempt to understand them and describe them may not always be accurate or correct. Which is not what you’re asking about. Unlike civil law, we didn’t create the laws of physics, we’re just trying to figure out what they are.
(Correct me if I’m wrong, sunacres, but) I think what he means – by saying “by definition the laws of physics will always be true” – is that if a “law” changes over time it is no longer a “law of physics” but a phenomenon in itself that follows some higher rule, or law, that must be studied.
In the past the laws of physics as we know them might have been different, but there had to have been some mechanism by which they changed. That mechanism is now open to study, and eventually the label “law” may be applied to it.
In a way, what you are asking about is the problem of induction, which has been discussed not merely for decades, but in fact for centuries, most famously by David Hume. There are many aspects to the problem of induction, but the one that’s relevant here is that it’s not entirely clear how we could have access to knowledge about the future given only knowledge of the past, given that, most would say, the future need not necessarily resemble the past. Given some assumed knowledge about some particular instances, it’s not clear what warrants us to conclude from this anything about further instances. For all we know, despite the way things have previously been, gravity will reverse tomorrow and unicorns will spontaneously spring into existence all over Australia. Knowledge of the future seems impossible to achieve (and the same holds for various other epistemological concepts).
Then again, to one of that skeptical bent, it’s not entirely clear how we could have access to knowledge of the past either, since the past need not necessarily be in any significant relation to our current observations, memories, etc. For all we know, right up until five minutes ago, everything was precisely as described in your favorite work of fiction; however, five minutes ago, things spontaneously switched over to, well, this, complete with implanted memories, dinosaur fossils, the whole shebang. (The omphalos hypothesis)
Personally, I might at times say that the labels of “the past” and “the future” are ordinarily used in such a way as that they (the past and the future) are essentially defined from our primitive knowledge/sensations/experience of the world, according to rules I couldn’t explicitly state but have some sense for nonetheless. The result of the setup would be that it becomes analytically true (i.e., true as a matter of pure definition) that knowledge about the future and past is attainable by the usual methods, the future will resemble the past, etc. But others will be less sympathetic to this point of view (as will I, at times).
I’m not sure that many ToEs would even do it. You’d need some proof (or understanding) that Laws at t+n will always be the same as Laws at t, for all t > ~0 (~ because you need time for things to settle down after the Big Bang.) I’m not aware that laws are written this way, or that there are meta-laws. Without this kind of treatment, I don’t see how you’d have a proof, but induction seems plenty good enough to give the desired level of confidence.
It seems anyone asking for a proof of anything doesn’t really understand. Perhaps a better question is what supports the assumption mentioned in the OP. Looking back in time is a good answer to that question.
I’ve heard it said that the cosmological principle says that the laws of physics, as we know about them here on Earth, will apply equally well on Mars, two stars over, or in the furthest galaxy, bearing in mind that the physical conditions in those locations will vary somewhat.
Sounds like what the OP is asking for is a temporal cosmological principle - that the laws of physics will apply equally well everywhere in time.
It’s really the same thing. Whatever we see in the farthest galaxy is light from many billions of years ago. So we have to make the assumption when we try to interpret the readings that the laws of physics were the same at that time as well as at that place.
I think he’s pointing out that if, for example, the speed of light is not in fact a constant forever and ever, we have more than just our observation of its speed in the last few decades; we are looking back in time over billions of years when we peer out to the stars, and it apparently has been the same constant all along.
If it were variable, it would seem more likely that it would have already been varying in the past. I think that’s good enough reason to provisionally believe that it will continue to be the same in the future, pending some (surprising) new data.
If you think that’s a good enough reason, then, hooray. You are willing to (provisionally) believe that what has held in the past will continue to hold in the future. You are willing to grant precisely the assumption that the OP has expressed skepticism about. I wouldn’t say there’s anything wrong with that, but it also does nothing in itself to assuage those who are less willing to grant such an assumption. That is, to one who expresses doubt about such assumptions, you have not provided any substantial reason to lower that doubt.
Science in all its glory is now so small shall defy the laws of nature. And now must be “new” sciences. Science creates science and so on. The singularity near? The great debate it seems to me maddening. The final frontier? Technology, as we watch our science expand…does everything expand. To what point. Everything imagined. Laws of nature, ha. Things not yet discovered. Not laws of nature. Laws of themselves. Things only pertinent to themselves. Not effecting anything else. SO small, we can not justify their presence yet because they dont affect anything else. Well, really, yes, I think they can and will change…everything theory. Its the going back that cant change. But then again I am a crazy alcoholic.
