tag:blogger.com,1999:blog-22973357.post3088190548281048647..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: Is faster-than-light travel possible?Sabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger320125tag:blogger.com,1999:blog-22973357.post-74452125938644365262021-03-23T11:58:29.684-04:002021-03-23T11:58:29.684-04:00Sorry for the delay, I had given up on this thread...Sorry for the delay, I had given up on this thread until just now I saw a new comment on it in the recent comments list.<br /><br />My comment which you refer to was in response to WS's original example. In my opinion it strongly suggests that WS example was invalid under Special Relativity due to the simultaneity conditions it imposes.<br /><br />You pose a new example. As I understand it, JimVhttps://www.blogger.com/profile/10198704789965278981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-38685246664885182812021-03-23T11:23:15.130-04:002021-03-23T11:23:15.130-04:00No, I am not reinterpreting anything. I am merely ...No, I am not reinterpreting anything. I am merely stating the obvious, if you arrive at a contradiction, you did something unphysical. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75111577226775900162021-03-23T11:01:39.372-04:002021-03-23T11:01:39.372-04:00Is the theory you're referring to here the &qu...Is the theory you're referring to here the "reinterpretation principel" discussed at https://en.wikipedia.org/wiki/Tachyon#Reinterpretation_principle ? The wikipedia page says "this principle is not widely accepted as resolving the paradoxes", citing some sources that mention the "tachyonic antitelephone" paradox at https://en.wikipedia.org/wiki/JesseMhttps://www.blogger.com/profile/09993568347649474812noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-83588904510418671062020-08-30T03:01:09.868-04:002020-08-30T03:01:09.868-04:00c to infinity is not a physically meaningful limit...c to infinity is not a physically meaningful limit because c has units. You have to take a limit of the form v/c -> 0 instead. This is the non-relativistic limit and it does not have the properties that you claim it has. Math matters. Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-51433310871341321282020-08-29T14:31:17.956-04:002020-08-29T14:31:17.956-04:00We can make the right side of Einstein field eq. 0...We can make the right side of Einstein field eq. 0 by making all terms of the energy-momentum tensor 0. But that's mathematically equivalent with having speed of light c -> infinity and a non-zero energy-momentum tensor. Could we talk of a spooky action at a distance in the context of GR if there exists such a path of 0 E-p tensor?<br /><br />Same question when E-p tensor has all terms Catalinhttps://www.blogger.com/profile/06192244112905762189noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-25903802502927004202020-08-29T12:05:47.015-04:002020-08-29T12:05:47.015-04:00Most of the subject matter is just narrative, only...Most of the subject matter is just narrative, only some of which has "evidence" supporting the likelihood that it might indeed be proof. <br />If the narrative/theory does not make sense, maybe it should be tweaked until the next common sense logical juncture is encountered progression and leads to the next paradigm, etc. to be resolved. Hence, I like your notion of an approximation Michaelhttps://www.blogger.com/profile/06062130522411480102noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-34747586696624129462020-07-11T23:31:44.627-04:002020-07-11T23:31:44.627-04:00Perhaps things are different in deep space? Since ...Perhaps things are different in deep space? Since no one went there (yet), how do we know that a ship accelerating won't surpass c? Relativity prohibits it of course, but Relativity and Reality may be two different things if we don't have clear experimental proof. Clearly Relativity works on Earth and nearby, but would it work far from large mass? Any proof, and I mean direct proof? The Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-27968311303582086492020-06-21T12:57:50.516-04:002020-06-21T12:57:50.516-04:00Well, I did do the math wrong…[much confusion] … I...<i>Well, I did do the math wrong…[much confusion] … I still don't which is the more realistic case.</i><br /><br />B and C are irrelevant. A and D are receding from each other at a relative speed of (say) c/2, and A sends a signal to D at speed 4c in terms of A’s rest frame, and D immediately relays it back to A at speed 4c in terms of D’s rest frame, and the signal arrives back at A prior Amoshttps://www.blogger.com/profile/00595591283398023248noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-25586756971657318802020-06-21T00:11:26.991-04:002020-06-21T00:11:26.991-04:00Well, I did do the math wrong in the above. That, ...Well, I did do the math wrong in the above. That, is in my hen-scratched notes I got d = L'/(n-1) but somehow transposed it to L'/(n+1) in the next equation. So the true condition for the message from A to reach D in C-D's frame before C reaches A in C-D's frame is simpler and more intuitive: 1 >= n.<br /><br />So unless the train travels at the speed of light or faster, A'JimVhttps://www.blogger.com/profile/10198704789965278981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-10597319914660741602020-06-18T23:07:01.663-04:002020-06-18T23:07:01.663-04:00WS, on a long walk to a market and back (with a fa...WS, on a long walk to a market and back (with a face mask on) I started to agree with your example, and resolved to do some Lorentz calculations when I had a pencil and paper. As I said, I like definite numbers, so the tunnel length is L, the train moves at c/n, the train length is L over sqrt(1-(1/n^2)) = L0. So A & B see the train length as L, and C & D see the tunnel length as L'=LJimVhttps://www.blogger.com/profile/10198704789965278981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-43594797946960857012020-06-18T10:52:07.026-04:002020-06-18T10:52:07.026-04:00WS, as I see it, if the train is longer than the t...WS, as I see it, if the train is longer than the tunnel in their mutual rest frame, then when A and C coincide, D is well past B in C-D's frame. As I said earlier, I prefer to think of the rest frame lengths as the true lengths, and Lorentz effects being due to the impossibility of measuring those lengths from a frame moving relative to it. (Of course, some would say the true length is JimVhttps://www.blogger.com/profile/10198704789965278981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-38746882231296715202020-06-18T06:34:34.799-04:002020-06-18T06:34:34.799-04:00Plankalkül: Still being silly. Non-living matter c...Plankalkül: Still being silly. Non-living matter can <i>move</i> against the tide, if it has momentum or internally generated energy.<br /><br />Your premise is wrong. It doesn't make a difference if a living thing built a non-living object; the fact that any non-living object can do what you claim only living objects can do is proof that you are wrong. <br /><br />I don't care if you areDr. A.M. Castaldohttps://www.blogger.com/profile/17988116835722393503noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-59802778246662449252020-06-18T02:44:40.107-04:002020-06-18T02:44:40.107-04:00No answer is also a answer ...No answer is also a answer ...weristdashttps://www.blogger.com/profile/04693023273675933748noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-71441687578752002822020-06-17T21:15:34.379-04:002020-06-17T21:15:34.379-04:00"I am marking the time as t-2 when A and C co...<em>"I am marking the time as t-2 when A and C coincide"</em><br /><br />Are you saying <em>both</em> Alice and Carol synchronize their clocks to both read <strong>t2</strong>? That's fine, but remember that Bob and Dave then show different times on their clocks when they coincide.<br /><br />When Dave coincides with Bob, Dave's clock reads <strong>t0</strong> while Bob's Wyrd Smythehttps://www.blogger.com/profile/06694506351266400927noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-70481062117309328102020-06-17T18:09:42.851-04:002020-06-17T18:09:42.851-04:00"Don't be silly."
Oh what a nice we..."Don't be silly."<br /><br />Oh what a nice welcome.<br /><br />Your argumentation of the kind "No one sees a problem here but you" doesn't really convince me.<br /><br />OK I made one mistake. At first I thought Frau Hossenfelder meant reversing a process using the same particles. But it's the same problem using different particles, too.<br /><br />The point is: Plankalkülhttps://www.blogger.com/profile/06436729620905258626noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-54309011647530370952020-06-17T17:09:06.389-04:002020-06-17T17:09:06.389-04:00I don't see how you can convince me that I can...<i>I don't see how you can convince me that I can arrive back at Earth either before or after I left depending on which frame you chose.</i><br /><br />It isn’t about “choosing frames”, it’s about understanding the logical consequences of the (counterfactual) proposition that you can move superluminally in the context of special relativity. The principle of relativity implies that if it wereAmoshttps://www.blogger.com/profile/00595591283398023248noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-1414601343024778722020-06-17T11:20:14.422-04:002020-06-17T11:20:14.422-04:00In response to WS:
Just as you marked the time as...In response to WS:<br /><br />Just as you marked the time as t0 in both frames when B and D coincided, I am marking the time as t-2 when A and C coincide, and moving forward in C-D's frame (with the AoT) at that point. At that instance in the C-D frame, D is past B and cannot coincide with it, in the case that the train and tunnel have equal lengths in the same rest frame. If the train is JimVhttps://www.blogger.com/profile/10198704789965278981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-46680509553614989622020-06-17T01:16:12.785-04:002020-06-17T01:16:12.785-04:00Yes, the effect is because the two frames see simu...Yes, the effect is because the two frames see simultaneity differently. Only Alice-Bob see the tunnel doors close simultaneously. If they take a snapshot of the enclosed train at that moment, what they see is what I described above.<br /><br /><i>"Let's consider the time t-2,"</i><br /><br />Remember, only Carol's clock shows <b>t2</b>. Alice's clock shows <b>t0</b>. So doesWyrd Smythehttps://www.blogger.com/profile/06694506351266400927noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-88270092100138516932020-06-16T23:26:10.166-04:002020-06-16T23:26:10.166-04:00When I arrive at PC and head back towards Earth, t...<i>When I arrive at PC and head back towards Earth, that's the frame I travel in and will arrive in.</i><br /><br />You haven’t identified a frame, and your travel and arrival can be described (with the same laws of physics) in terms of any inertial frame. There is nothing special or unique about the frame in which the Earth happens to be at rest (unless you are a geocentrist).<br /><br /><iAmoshttps://www.blogger.com/profile/00595591283398023248noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-10251823424531698422020-06-16T15:14:14.488-04:002020-06-16T15:14:14.488-04:00Wyrd Smythe: "Here's where it gets twisty...Wyrd Smythe: "Here's where it gets twisty. Remember, the train fits in the tunnel, such that doors could be briefly (really briefly) closed. This means, according to Alice-Bob, some version of Carol-Dave fits in the tunnel."<br /><br />But according to C&D, no so such instant exists. (Assuming the train and tunnel are the same length in a frame in which both are at rest.) Each JimVhttps://www.blogger.com/profile/10198704789965278981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-17926531680025660422020-06-16T04:36:41.987-04:002020-06-16T04:36:41.987-04:00Wyrd Smythe2:22 AM, June 16, 2020
"Well, no. ...Wyrd Smythe2:22 AM, June 16, 2020<br />"Well, no. Moving sub-light isn't a problem."<br /><br />What do you argue again the obvious claim that all is moving with exact the speed of light versus photons/wavefronts?<br /><br />How will you defend your assertion that something is moving sub-light - versus photons/wavefronts?<br /><br />Why do you exclude photons/wavefronts as referenceweristdashttps://www.blogger.com/profile/04693023273675933748noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-86000651162001018722020-06-16T02:22:34.397-04:002020-06-16T02:22:34.397-04:00@JimV:
"Very confusing."
Special Relat...@JimV:<br /><br /><i>"Very confusing."</i><br /><br />Special Relativity is confusing until one develops an intuition for the geometry of it.<br /><br /><b>By definition</b> the moment Dave coincides with Bob is arbitrarily labeled <b>t0</b> on both Dave's and Bob's clocks. Due to Lorentz transformations, the clocks in both frames indeed "are in some relationship" withWyrd Smythehttps://www.blogger.com/profile/06694506351266400927noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-5470265190030353342020-06-15T20:09:57.522-04:002020-06-15T20:09:57.522-04:00From Wryd Smythe's original A-B, C-D comment:
...From Wryd Smythe's original A-B, C-D comment:<br /><br />"Call t0 the moment Dave and the front of the train, having passed through the tunnel, reaches Bob. The train continues, Dave passes Bob, and -- ON THE TRAIN -- at some later time t2, Carol and the train's end reach Alice at the tunnel mouth.<br /><br />But according to Alice and Bob, at t0, Carol's clock on the train readsJimVhttps://www.blogger.com/profile/10198704789965278981noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-23894469806823218942020-06-13T02:46:10.551-04:002020-06-13T02:46:10.551-04:00@Amos . . .
Superluminal travel is possible in...@Amos . . . <br /> Superluminal travel is possible in the imaginary spacelike interval<br /> (that can be derived from the counterfactual premise of in the <br /> context of special relativity) Such travel solves the causal paradox.israel sadovnik socratushttps://www.blogger.com/profile/05455782761752129698noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-23936579477081502382020-06-13T01:23:38.738-04:002020-06-13T01:23:38.738-04:00Its a mistake to use physics to try to prove the e...Its a mistake to use physics to try to prove the existence of God. The literalism of that effort circumscribes God into physics. It makes God into a physical being. In so doing you loose the essential mystery of God. You minimize and constrict God via physical processes, You wind up with a tiny God. Instead of a Christian God you wind up with a modern day Zeus.<br /><br />I think a lot of Steve Bullfoxhttps://www.blogger.com/profile/13990244011256349875noreply@blogger.com