# Scientific respectability and Velocity C **URL:** \ **Category:** Factual Questions\ **Created:** [November 5, 2001, 10:03pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679 "2001-11-05T22:03:57Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Scott\_Dickerson](https://avatars.discourse-cdn.com/v4/letter/s/f04885/32.png) [@Scott\_Dickerson](https://boards.straightdope.com/u/Scott_Dickerson)\ **Post date:** [November 5, 2001, 10:03pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/1 "2001-11-05T22:03:57Z")
In a nutshell: Why is it considered an absolutely central test of scientific rationality to accept the proposition that “no information can travel faster than velocity C, the speed of light in a vacuum”? This is not intended as a Great Debates entry, and I am not asserting that the proposition is false. Furthermore, I have a good enough education in physics to know how this conclusion arose–Michaelson/Morley experiment, decaying microparticles lasting longer than they should, etc. I realize and appreciate the general elegance and simplicity of Einsteinian special relativity and its obvious predictive power. BUT-- the proposition is, after all, an utterly general and absolute assertion based upon the observed behavior of matter and energy: concrete things. Yet the proposition is defended as if it had attained the status of an a priori truth. We’re not talking about “all bachelors are unmarried” (true by stipulation, by the meanings of the words), nor “2+3=5” (true in that once it is empirically observed in even one case, its falsity becomes inconceivable). [The two examples correspond to Kant’s analytic and synthetic a priori, if anyone cares.] It seems that this proposition ought to be regarded as “just” another of the falsifiable proto-laws of science, which might well require fine-tuning or later subsumption under some other generalization; just as Galilean-Newtonian generalizations were subsumed under those of Einstein. It is not (literally) inconceivable that certain exotic energies or materials might be immune from relativistic effects; or that “C” might be locale-dependent to some nonzero degree; or even that its value might fluctuate between certain parameters. If we know the value of “C” to (say) one part in a billion, how can we justify any conclusion as to its value a billion times “finer-grained”? We have transmitted radar-like pulses over solar-system distances and received them back, measuring their speed of propagation directly; but such distances are pretty small potatoes in this big universe. My point, again, is not that Einstein is wrong and the nuts are right. I would just like to know why this has become such a touchstone (a dogma?) in scientific culture. Have I overlooked some purely logical element? Why would it be not just naive but actually obtuse to regard the cited proposition as only another well-supported hypothesis? ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [November 5, 2001, 10:29pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/2 "2001-11-05T22:29:37Z")
What is a theory but a very well-supported hypothesis? Anyway, Relativity states that nothing which carries information, such as matter, can travel faster than c without violating causality. So, in order for something to travel faster than c, either causality would be violated, or Relativity would be wrong. I’m going to assume you’re asking then, why isn’t Relativity wrong? Well, it could be, but we don’t have anything better to describe the Universe. Yet. The reason it’s considered a test of scientific rationality is that it’s so counter-intuitive. Gravity always pulls. Momentum is conserved. Do you have any evidence that the c speed-limit is considered more dogmatic than either of those principles? It takes faith in science to accept something which the evidence points to, even if it isn’t clear in your mind how it works. Believing that stuff falls down is just as true, scientifically, but anyone will believe it because it’s so intuitive. I’m interested in just what exactly you consider “scientific culture”, and just what you have in mind when you say it’s become a touchstone. ---
**Author:** ![bryanmcc](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@bryanmcc](https://boards.straightdope.com/u/bryanmcc)\ **Post date:** [November 5, 2001, 10:40pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/3 "2001-11-05T22:40:10Z")
I don’t think that the absolute and limiting nature of _c_ is regarded as an a priori truth. Most any qualified scientist will admit that such claims _may_ be shown to be incorrect, or at least require qualification, and, in fact, many are working to do so. However, many scientists (especially when dealing with lay people, as here on this board) do defend the absolute quality of _c_ with near-religious zeal. I think this is likely due to the fact that anti-science types (Creationists, various wackos in general) attack Einstein with equal zeal. He and his work are seen as the paragon of modern science, and the lynchpin to the downfall thereof. It seems like every two or three weeks I see a story in the press about someone who has “accelerated” light, slowed light, transmitted information faster than light, or otherwise disproved Einstein. These are invariably (or, at least, have been so far) misleading at best, and flat out wrong at worst. Scientists, in frustration, respond time after time with increased vehemance, “Hey! Nothing can travel faster than light!” So, I believe that they respond with such emotion due to the fact that they are required to defend it so often to such poor attacks. I, for one, don’t blame them. All current knowledge, and many, many supporting experiments, bear out the constancy of the speed of light, and the unattainable limit that it sets. But I would gladly accept any clear, well documented, repeatable experiments that clearly disprove Einstein. And, I think, so would they. -b ---
**Author:** ![JS\_Princeton](https://avatars.discourse-cdn.com/v4/letter/j/57b2e6/32.png) [@JS\_Princeton](https://boards.straightdope.com/u/JS_Princeton)\ **Post date:** [November 6, 2001, 1:49am UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/4 "2001-11-06T01:49:05Z")
The Lorentz transformations were invented to take into account electrodynamics. This is what you are missing in your argumentation. Basically, electromagnetic waves were a mathematical consequence to Maxwell’s Equations. They were deduced and their speed was found to be one over the squareroot of the electric permitivity of freespace times one over the squareroot of the magnetic permitivity of freespace. This number was… amazingly enough… discovered to be the speed of light! EUREKA! so it’s said. Now the problem came that it didn’t matter what Galilean reference frame you were in, electrodynamics worked exactly the same. This is a result of magnetism and electricity basically being the same phenomenon seen in different reference frames. In fact, you get the right reference frame with respect to a charged particle you get a totally electric field (if you are at the same velocity) if not, you get a mixture (due to the peculiarity of the force eqns for these phenomenon). So, here’s the thing: equivalence can be postulated without even appealing to friggin Michaelson and Morley… in fact Eistein, it seems, didn’t use the experiment at all. He was somewhat nonplussed when they told him about their peculiar results. “Of course that’s the way the world works! I could have told you that!” How did he come up with it? Well, basically he figured out that the velocity of the observer and the velocity of the charged particle could not be parsed. When he was 19 he was biking along (so the story is told) and thought, “Eef I travel the speed of light, I could see zees stationary waves, zee crests an zee troughs.” But that would violate Maxwell’s electromagnetic waves. “Zometing’s NOT right!” quoth young Einstein. In fact, what was not right was the fact that people did not have an equivalence principle for electromagnetism. The consequence of this is therefore that the speed of light is the fastest thing there is. It’s electrodynamics that does it! ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 6, 2001, 3:02am UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/5 "2001-11-06T03:02:21Z")
Just in case it’s not clear what **Achernar** meant: Violating causality would mean that you can get information from the future to the past (or future to present, or present to past, or near past to distant past, or… You get the point.). Most folks, in turn, believe that it’s impossible to get information to flow the “wrong way”, as that could potentially lead to all sorts of paradoces. That’s not to say that it’s necessarily impossible, though: Many scientists are actively researching the possibility, and the only result thus far is a definite “maybe”. One thing everyone agrees on, though, is that even if it is possible, it’s awfully difficult, and there’s certainly not yet been any experimental evidence presented for the possibility. ---
**Author:** ![Scott\_Dickerson](https://avatars.discourse-cdn.com/v4/letter/s/f04885/32.png) [@Scott\_Dickerson](https://boards.straightdope.com/u/Scott_Dickerson)\ **Post date:** [November 6, 2001, 7:40am UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/6 "2001-11-06T07:40:43Z")
I appreciate the replies, which answered my question very fully. Reading a little into the “electrodynamic” explanation, and separately the “causality-violation” explanation as well, are the following statements accepted as premises by those scientists with the greatest involvement in these matters, presumably physicists? (1) “Information” is ultimately reducible to some localized state (ie, “pattern”) of matter/energy (becoming “known” information when the locale happens to be one’s own cortex). Corollary: Nothing of any possible consequence (= nothing “real”) exists that is not wholly analyzable in terms of matter/energy. (2) Matter/energy modifications are never propagated except in accordance with Maxwell’s Equations (perhaps as later amended to some degree). Corollary: Ordinary mechanics and kinetics ultimately falls under these equations, as special cases. (3) Matter/energy modifications cannot be “understood” (“parsed”?) as propagating at C-plus velocities, as this would strictly entail at least the possibility of causality violations. (4) For a priori logical reasons, causality violations cannot possibly occur. Is this–very roughly–the logical case for the “C limit”? ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [November 7, 2001, 12:19am UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/7 "2001-11-07T00:19:03Z")
> [@](#): > > 1. “Information” is ultimately reducible to some localized state (ie, “pattern”) of matter/energy (becoming “known” information when the locale happens to be one’s own cortex). > Corollary: Nothing of any possible consequence (= nothing “real”) exists that is not wholly analyzable in terms of matter/energy. The corollary is probably accepted in something roughly like this form by most physicists, at least as a working hypothesis when it comes to doing science. The previous statement is more awkward; the word “localized” rings my alarm bells for a start. > [@](#): > > (2) Matter/energy modifications are never propagated except in accordance with Maxwell’s Equations (perhaps as later amended to some degree). Corollary: Ordinary mechanics and kinetics ultimately falls under these equations, as special cases. While Maxwell’s Equation are far from the final word, all the additional laws/equations/whatever that we know about share the same relevant mathematical property with them. So, yes, the gist of these statements is correct. > [@](#): > > (3) Matter/energy modifications cannot be “understood” (“parsed”?) as propagating at C-plus velocities, as this would strictly entail at least the possibility of causality violations. I’m not sure I understand this. > [@](#): > > (4) For a priori logical reasons, causality violations cannot possibly occur. Causality arguably comes closer to being _a priori_ than anything else in science: could science even exist in a totally acausal universe? However, philosophers, and some physicists, spend a great deal of effort distinguishing between different types of causality. Certainly many naive conceptions of it have taken a battering at the hands of quantum mechanics. This alone makes physicists wary of assuming anything about it in general. It is true that they will use it as a working hypothesis - in arguments like this, for instance - but few would fully accept such a strong statement as this. If anything, the discovery of relativity (and QM) has tended to make physicists distrust arguments for anything being _a priori_ true in their subject. ---
**Author:** ![JS\_Princeton](https://avatars.discourse-cdn.com/v4/letter/j/57b2e6/32.png) [@JS\_Princeton](https://boards.straightdope.com/u/JS_Princeton)\ **Post date:** [November 8, 2001, 5:10am UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/8 "2001-11-08T05:10:08Z")
> [@](#): > > \*Originally posted by Scott Dickerson \* > \*\* > > (2) Matter/energy modifications are never propagated except in accordance with Maxwell’s Equations (perhaps as later amended to some degree). Corollary: Ordinary mechanics and kinetics ultimately falls under these equations, as special cases. > \*\* To a point. Since we have unification of the strong force and the electroweak, we are pretty confident that relativity is a good cover-all for these guys. Gravity was expanded by good ol’ Einstein in GR. It was starting with the evidence that Maxwell’s Eqs. behaved in a certain way that allowed for further developments in relativity. Think of it this way: Maxwell’s Eqs. predicted a constant velocity speed limit of C everywhere in order for Galilean relativity to be true. Since these eqns. worked so well, we “ran with the ball” and ended up with the bizarre concepts of SR and GR that ended up being proved experimentally and shocked the world. ---
**Author:** ![FriendRob](https://avatars.discourse-cdn.com/v4/letter/f/ecc23a/32.png) [@FriendRob](https://boards.straightdope.com/u/FriendRob)\ **Post date:** [November 8, 2001, 4:37pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/9 "2001-11-08T16:37:34Z")
> [@](#): > > \*Originally posted by Scott Dickerson \* > \*\* > (1) “Information” is ultimately reducible to some localized state (ie, “pattern”) of matter/energy (becoming “known” information when the locale happens to be one’s own cortex). > Corollary: Nothing of any possible consequence (= nothing “real”) exists that is not wholly analyzable in terms of matter/energy. > \*\* “Information” is not really what the physicist is interested in. Rather, it is the “pattern of matter/energy”. The corolary is not necessarily true, either: physicists just limit ourselves to those phenomena which _can_ be analyzed in terms of matter/energy. > [@](#): > > \*\* > (2) Matter/energy modifications are never propagated except in accordance with Maxwell’s Equations (perhaps as later amended to some degree). Corollary: Ordinary mechanics and kinetics ultimately falls under these equations, as special cases.\*\* Well, if you replace “Maxwell’s Equations” with “the laws of physics”. Maxwell’s Equations just describe light (or rather electromagnetism), and for a better description you need to use QED (quantum electrodynamics) even for light. Really, it is the opposite of the Corollary: Maxwell’s Equations are a special case of QED. But all of the modern theories have the same spacetime structure built into them as that of SR. > [@](#): > > \*\* > (3) Matter/energy modifications cannot be “understood” (“parsed”?) as propagating at C-plus velocities, as this would strictly entail at least the possibility of causality violations. > \*\* Right, assuming of course that spacetime works the way we think it does. But there’s lots of evidence that it does. > [@](#): > > \*\* > (4) For a priori logical reasons, causality violations cannot possibly occur. > \*\* Right again. ---
**Author:** ![SCSimmons](https://avatars.discourse-cdn.com/v4/letter/s/e495f1/32.png) [@SCSimmons](https://boards.straightdope.com/u/SCSimmons)\ **Post date:** [November 8, 2001, 5:26pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/10 "2001-11-08T17:26:13Z")
It doesn’t have anything directly to do with matter-energy, actually, but rather with the interrelationship of space and time and the relativistic notion of _interval_. The interval between two events in spacetime is invariant in relativity-that is, two different reference frames will measure the same interval between any two events, although both the space and the time differences between the events will generally _not_ have the same measurement from that point of view. When you talk about information flow exceeding the speed of light, what this means in terms of relativity is that an event can influence another event which is separated from it by a spacelike, rather than a timelike, interval. The problem here is that when two events are separated by a spacelike interval, _the question of which event is prior is relative to the reference frame_. I’m not going to try to hurt anybody’s brain with the math. The upshot is that, if you allow this kind of information transfer, you can set up situations where information gets back to the original worldline at a prior point, which sets up causality paradoxes (like the infamous grandfather paradox, but with information rather than bullets). For instance, A and B are motionless with respect to each other at a distance of one light-year. A sends B a message, “I tried the experiment X we discussed, and it destroyed my equipment. Dumb idea,” using our hypothetical super-speed radio, and B receives the message one minute later. B is upset about A’s expensive apparatus being destroyed, but fortunately he has a great idea. By forwarding the message to spacecraft pilot C, who is traveling at the right speed & direction, with instructions to forward the message back to A (all by the same super-speed radio, of course), he can arrange for the message to get back to A _ **before it was sent** _. Naturally, A then decides not to do experiment X after all. But wait-then why would he send the original message? Physicists would like to believe that this can’t happen. So if relativity is correct, super-speed communication of this kind is impossible, regardless of whether it involves matter & energy or thought waves & ESP. C’est la vie. ---
**Author:** ![Scott\_Dickerson](https://avatars.discourse-cdn.com/v4/letter/s/f04885/32.png) [@Scott\_Dickerson](https://boards.straightdope.com/u/Scott_Dickerson)\ **Post date:** [November 8, 2001, 11:29pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/11 "2001-11-08T23:29:19Z")
So maybe the quickest and dirtiest answer is… 1. To exceed C allows “arriving” prior to “leaving” in terms of some observer (who thus “sees” a “flipped” causal sequence). 2. This would allow for time-reversed causal interaction, as viewed by the observer. 3. Which leads to self-stultifying situations, the “descriptions” of which are uninterpretable. 4. Therefore premise #1 must be false. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [November 9, 2001, 5:33pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/12 "2001-11-09T17:33:05Z")
> [@](#): > > The upshot is that, if you allow this kind of information transfer, you can set up situations where information gets back to the original worldline at a prior point, which sets up causality paradoxes If there is a preferred frame of reference for FTL communication, these paradoxes can be avoided. While there’s no evidence of any preferred frame of reference in terms of the equations of physics, it can’t be ruled out. As long as any FTL communication is instantaneous or slower in the preferred frame of reference, it won’t matter that it may be “backwards” in time for some other frame of reference. The communication in the other direction will always be _slower_ than instaneous. > [@](#): > > (4) For a priori logical reasons, causality violations cannot possibly occur. It’s not hard to imagine a universe closed in the time-like dimension. Think of a torus with time going around the hole. You’d have to enforce periodic boundary conditions in the time dimension, but I don’t see any reason why that wouldn’t be possible. ---
**Author:** ![Scott\_Dickerson](https://avatars.discourse-cdn.com/v4/letter/s/f04885/32.png) [@Scott\_Dickerson](https://boards.straightdope.com/u/Scott_Dickerson)\ **Post date:** [November 9, 2001, 7:30pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/13 "2001-11-09T19:30:20Z")
I understand that one can “visualize” a torus-like time dimension. But what I’m gleaning from some of the other posts–and maybe I’m just over-gleaning–is that the concept of a causal “flow” having a single direction, universally recognized as such, is so near the rock-bottom of our picture of Reality that we would tease out almost ANY alternative before admitting the possibility of a violation. (Well, I realize a toroidal time would still have a causal flow in one “direction.” I suppose what we reject–rightly or wrongly–is the notion that a causal sequence originating in the Now and extending futurewards, could be continuous with a chain coming toward us “from the past.” Whoa–need a few technical terms here re: relative positions in time that I don’t happen to know!) BTW, I appreciate these many thoughtful and serious answers! ---
**Author:** ![SCSimmons](https://avatars.discourse-cdn.com/v4/letter/s/e495f1/32.png) [@SCSimmons](https://boards.straightdope.com/u/SCSimmons)\ **Post date:** [November 9, 2001, 8:08pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/14 "2001-11-09T20:08:46Z")
> [@](#): > > \*Originally posted by ZenBeam \* > **If there is a preferred frame of reference for FTL communication, these paradoxes can be avoided.** Good point, ZenBeam. There are some other rather odd paradoxes that you could then dig up, but they’re not as mind-bending as causality violation, or even as the Copenhagen interpretation of quantum mechanics, I’d imagine. 🙂 ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [November 9, 2001, 10:40pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/15 "2001-11-09T22:40:13Z")
> [@](#): > > \*Originally posted by ZenBeam \* > **If there is a preferred frame of reference for FTL communication, these paradoxes can be avoided.** I wanted to make it clear that what **ZenBeam** is proposing here is a _violation of Relativity_. One of the two fundamental assumptions of Special Relativity is that there is no such preferred frame. As I mentioned earlier, either super-c information exchange violates causality, or Relativity is wrong. ---
**Author:** ![ZenBeam](https://avatars.discourse-cdn.com/v4/letter/z/3ab097/32.png) [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)\ **Post date:** [November 10, 2001, 1:38am UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/16 "2001-11-10T01:38:09Z")
General Relativity _predicts_, given sufficient mass in the universe, a closed universe. In a closed universe, there _has_ to be a preferred frame of reference. To convince yourself of this, try drawing a Minkowski diagram on a piece of paper, and rolling it into a cylinder so that the spatial axis in one frame of reference closes on itself. i.e., it forms a continuous line around the cylinder. The spatial axis from _any other_ frame of reference will not form a closed loop, but will rather spiral around the cylinder. OK, this has no particular relation to FTL communication, but not having preferred frame isn’t _that_ fundamental. Also, a preferred frame which only manifests itself in the context of FTL communication doesn’t contradict any measurements, because no FTL measurements have ever been made (AFAIK :)). **SCSimmons** , what “odd paradoxes” are you referring to? ---
**Author:** ![SCSimmons](https://avatars.discourse-cdn.com/v4/letter/s/e495f1/32.png) [@SCSimmons](https://boards.straightdope.com/u/SCSimmons)\ **Post date:** [November 10, 2001, 1:57am UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/17 "2001-11-10T01:57:35Z")
> [@](#): > > \*Originally posted by ZenBeam \* > \*\*SCSimmons, what “odd paradoxes” are you referring to? \*\* I think I’ve hijacked the thread enough for the moment. I’ll leave it as an exercise for the student. 😃 Just add an instantaneous communicator to the classic ‘traveling twin’ paradox and ponder how much weirder it gets. 🙂 But it _is_ a soluble problem, in that you can work out a logically coherent solution. (You want to particularly look at the situation where the stationary twin is in the preferred reference frame, and the travelling twin accelerates into a reference frame where communication in one direction is ‘backwards in time’ relative to that frame.) ---
**Author:** ![Achernar](https://avatars.discourse-cdn.com/v4/letter/a/e274bd/32.png) [@Achernar](https://boards.straightdope.com/u/Achernar)\ **Post date:** [November 10, 2001, 2:16am UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/18 "2001-11-10T02:16:36Z")
I concede that I don’t know enough about GR yet to defend myself, so I’m with you, **ZenBeam**. I didn’t realize that a closed Universe necessarily meant it was closed on the time axis as well. I should have said that a preferred reference frame is a _violation of Special Relativity_. So GR violates one of the fundamental assumptions of SR? Cool. Although now I tend to wonder why it’s still called Relativity. That Minkowski diagram experiment would not convince me, since I don’t have any non-Euclidean paper to work with. But your word is good enough for me. ---
**Author:** ![Scott\_Dickerson](https://avatars.discourse-cdn.com/v4/letter/s/f04885/32.png) [@Scott\_Dickerson](https://boards.straightdope.com/u/Scott_Dickerson)\ **Post date:** [November 10, 2001, 7:14pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/19 "2001-11-10T19:14:55Z")
This stuff is way cool. Idnit? To ease any concerns about hijacking–and thanks for those concerns–as OP my concept of this thread (somewhat clarified) is this: “Given experimental support for GR and the C-limit aspect thereof (as well as the role of C in Maxwell’s Equations, etc.), what is the LOGICAL STATUS of the proposition that no causative influence (including that special kind called ‘information’) can connect two points in space in less of a time interval (for any possible observer) than a C-travelling entity would take.” By “LOGICAL STATUS” I’m trying to get a grip on the idea that some propositions, not true in an a priori analytical sense, become classified as true in the way that “2+3=5” is true–an empirical generalization that, once accepted at all, cannot be conceived to be false. Is the proposition above (NB, in its most ABSOLUTE form) so interwoven with a century and a half of physics that no real modification or weakening is conceivable? In other words, is it like “There’s no such thing as perpetual motion” (definitely true), or more like “There is no life on Mars” (probably true, possibly false: wait and see)? ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [November 10, 2001, 11:50pm UTC](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679/20 "2001-11-10T23:50:52Z")
> [@](#): > > \*Originally posted by Scott Dickerson \* > “There’s no such thing as perpetual motion” (definitely true) Why is this definitely true? While, possibly without exception, professional physicists accept and believe the 2nd Law of Thermodynamics, very few would assert that violations are impossible in the sense of “cannot occur in **all** conceivable universes.” Personally, while I regard neither as likely nor either as impossible in this sense, perpetual motion seems generally easier to swallow than a casuality violation. [Next page](https://boards.straightdope.com/t/scientific-respectability-and-velocity-c/91679.md?page=2)