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Iggy: ...Blah, blah, blah... You're a little late in the game to come back to the bullet vs light illustration. And I'm the one who said that "there is no cumulative velocity for light." Read the thread before you pop off. My examples: #4: #6: #12:

I take this to mean you believe that relativity is an all or nothing theory which is absolutely true in all respects and beyond all criticism. Your additional phrase, "like all of science" is quite obscure in meaning. None of science can be criticized without all of it being rejected? As to your second sentence, I don't need your permission to "pick and choose" the parts of relativity which I choose to criticize, as summarized above. And those parts do not invalidate my acceptance of GR's improved coordinate system for predicting the effects of gravity or SR's well established constancy of lightspeed.

When I said at the end of my last post, "That is all. I am done now." ... that was a signal from the author of the thread that either it could be shut down now by a moderator... not unusual for my threads... or contributors could focus on specifics to which I am allowed to reply. It clearly would not be fair to allow challenges to my last post, that I am not a "relativity denier," yet not allow my defense to each challenge, under my present gag rule restrictions. Just one example; Swansont said: "Intrinsic shape" means 'as it is' regardless of how it is observed or measured. As a "naive realist" I do not "... adopt a preferred frame of reference in which that shape is measured." ( I have a preference for being "at rest with" objects I observe and measure.) I realize that naturally occurring shapes of objects like planets do not depend on relativity's "frames of reference" for their properties, including dimensions and distances between such objects, etc. If the above reply violates (edit) 'my' gag rule, you can just ban me now and be done with it.

I will not allow such misrepresentation. For the record, I am not a "relativity denier." I accept that GR is an improvement over Newtonian physics in calculating and predicting the movements of masses and light around other masses. The math and physics work well with the coordinates for space and time based on the GR model. I deny that mass curves something 'in the real world' called "spacetime." I accept that the speed of light is constant as per SR. In fact I just learned more about its particulars by comparing different frames of reference in this thread and hearing the answers. I deny that the length contraction part of SR makes planets change shape, earth's atmosphere get thinner, or the distance between planets and the sun or between stars get shorter, as it might *appear* from relativistic frames. All of the above acceptance and denial is based on rational, reasonable thinking and what 'scientific realism' calls 'naive realism.' If the claim that a flattened earth is just as valid as a nearly spherical earth is based on the length contraction part of relativity as 'scientific realism', then I remain a 'naive realist', insisting that earth keeps its nearly spherical shape no matter how it might appear from extreme frames of reference. That is all. I am done now.

It is dropped. I wonder if there is anyplace in this forum where I can challenge "length contraction" on macro-scale without continuing censorship. Just wondering.

Me: "Speeding frames of observation do not change that, "in the real world."" So do speeding frames of reference change the naturally occurring cosmos and all of its properties or not? All this about what I have been told repeatedly... the authoritarian "argument"... does not answer this question. It requires rational thought and then a straight answer.

If you must have the last word, please address my last comment which you quoted: Edit; Ps: My thought experiment spontaneously emerged from considering the OP question about the ship traveling into the tail end of the light beam it was projecting... with no "pushing" it faster. I was corrected on that misconception. But meanwhile I had set up a scenario by which to compare what earth and the buoys would observe, both at rest relative to the test ship, with what the ship would observe, i.e., "contracted miles," for which it compensated to maintain earth-frame miles, which defines "miles" in the first place. I do accept that 'c' is constant in and of itself. It provides a constant standard for distance in light years. (The Alpha Centauri complex is 4+ light years away, and the sun is 8+ light minutes away. That remains constant.) Speeding frames of observation do not change that, "in the real world." My question concerned the discrepancy with what the ship would see with light traveling at 'c' relative to itself. From the ship's position at the 30th buoy (after a minute,) if it observed light traveling at 'c', it should have appeared to travel beyond the 60th bouy to a virtual 90th buoy, though it could only have gone 11,160,000 (to the 60th buoy) miles in a minute. So "apparent" miles are contracted "for the ship" as its "minutes" are expanded via its clock slowing down. I get it. You just hate to call earth-frame miles "length contracted miles", as seen from the ship. Oh well. Pps: You nailed it here: So did Spyman in his own words, previously quoted. My misconception was that constant 'c' meant that light should be observed from earth moving away from the ship at 'c' too. I was mixing frames in error.

I can and did ask "about the speed of light relative to the ship..." and also how it would look from earth's frame with the buoys place to preserve earth-frame miles between them. Earth sees the ship going 5,580,000 earth-miles and the light beam going 11,160,000 earth-miles in a minute of travel. My confusion, as already explained, was clarified by Spyman's explanation comparing the ship's frame to the frame of earth and the buoys at rest relative to earth and the ship. Light moves at 'c' relative to the buoys, which were 'brought to rest' relative to the ship dropping them. Review the part where the buoys' retros were fired until they lost 1/2 'c' of velocity, to be at rest relative to both ships (going the same velocity.) The buoys were placed to the specs of earth-frame miles as explained already in detail. I distinguished between that and length contracted miles in detail also. The ship was instructed to compensate for the difference, dropping them further apart than the length contracted 'miles' its frame would "see" at 1/2 'c' velocity. The spaceship was moving at 1/2 'c' relative to earth and the buoys. They had been 'brought to rest' relative to the ship, as I keep repeating. See above. Maybe you should read the thread before posting. I already addressed that. Here it is again from yesterday's post: ' No. No absolute frame. Ironically, the relativity of varying contracted dimensions is not absolute either. Things and the space between them are as they were naturally formed, not fluctuating with every different frame observing them. This, from Spyman on the 15th answered my basic question about the "push" of light: And this was very helpful in clarifying my misconception about SR: It's just very ironic for me that the "everything is relative" dictum is so absolute that the world/cosmos and all its relationships/distances between bodies loses its intrinsic reality... that things are as they are independent of observational frames. I'm done with this topic now.

Swansont: I ask the forum whether this is swansont's opinion, as a well educated physicist, or an indisputable fact. I will go with the former. The solar system was formed quite a long time before we came along and started observing it. The shape of earth and the distances between planets and the sun were well established long before intelligent life evolved on earth. Our observations and measurements don't change any of that.

swansont: “There is no such thing as a universal standard length.” I am not claiming and have never claimed that there is. “A mile”, however is derived from earth’s frame of reference... you know, 5280 feet... around 1/25,000the of earth’s circumference, etc. That is why I went into some detail on the set up, so that the layout of the buoys would be 186,000 earth-frame miles apart and then the ship & its beam would be observed from earth’s frame (taking into account, of course, the time for light to bring the “observation” back to earth.) My thought experiment is based on "seeing" what goes on here from Earth's frame. I know that the high speed frame will see it differently. Likewise a ship traveling at very high speed past the earth would probably see its diameter as length contracted, but that observation does not mean that earth's diameter does in fact become shorter, as we belabored to death in my previous threads. md: No need for your usual insulting condescension. My concern has always been with the distances between “things” (and object’s lengths) as they actually, intrinsically are, as contrasted with how they are observed (how they might appear) from relativistic speeds. That is why I said above: (Bold added.) swansont: To the first sentence, of course... obvious. In this thought experiment, light moves at ‘c’ relative to the earth and relative to the buoys. Your last sentence is false. Again, I do not dispute that a high speed frame will see it all differently, i.e, contracted. But “a mile” remains an earth-frame standard of length... Note: not a "universal standard of length." I think that “a mile” as seen from the ship should be called a length contracted 'mile' (l.c.'m.') and recognized as a relativistic distortion of the actual distance “a mile” as earth-frame derived. That l.c.'m.' will vary with the ship's velocity, but the standard earth mile will remain the same length. This recognizes the intrinsic lengths of objects as naturally formed and distances between them as, for instance between sun and planets as naturally spaced when the solar system was formed. No problem with "seeing" those distances differently as per relativistic effects. That is what my thought experiment was meant to advocate. Spyman, I find this post very helpful! Thank you. (I'd give you an approval point in the margin but for my belief that the popularity contest here is bogus anti-science.) My confusion about SR was the belief that it claims constant 'c' relative to any moving source or any observer, moving or not. Your statement above clarifies that: "From Earth's view there is nothing wrong with the fact that the lightbeam has only traveled 5,580,000 miles further than the ship after one minute." I had thought that the above dictum required the light to have traveled 11,160,000 from the ship, period, even as seen from earth. Again, thanks.

Again, I am not interested in what Newton thought about it. This is my own attempt to clarify questions in my mind, and I am not a stupid person. You seem to "need" me to "drop this." I am not interested in your needs. If I do not pursue this inquiry I will not understand the answers to what I am asking. . That may be true and I do not deny it. But just stating it as fact doesn't address my inquiry, last stated as: "How does the energy of its momentum transfer force to the sail with no mass to push against the matter of the sail? The sail absorbs the light, no doubt, but how does the 'push' manifest?" Thank you. I don't dispute those facts, but I still don't understand how a mass-less particle imparts force against (pushes) a mass (like the solar sail.) Momentum acting like mass without having mass still makes no sense to me. Edit; probably a silly question, but... Since we can't make photons sit still, we have no way of measuring them "at rest." So how can we be sure they they don't have an infinitesimal amount of mass? My thought experiment is based on "seeing" what goes on here from Earth's frame. I know that the high speed frame will see it differently. That's why I said that I'm not interested in the fact (probability?) that the ship will see less than 186, 000 miles between buoys. Not disputing what the crew would see. Asking what earth based observation would see. The earth-based mission was to place the buoys 186,000 earth-frame miles apart. So the crew would have compensated for apparent contraction, placing them more than 186,000 earth miles apart as seen from their frame. So the stage is set. In one minute the ship travels 5,580,000 earth-frame miles (to the 30th buoy) and its light beam travels 11,160,000 earth-frame miles (to the 60th buoy.) As earth sees it then, the light beam has only traveled 5,580,000 miles further than the ship. Yet relativity insists that the light has traveled, at constant 'c' 11,160,000 earth-frame miles from the ship in that minute? Or does constant 'c' relative to the seeding ship only hold true for length contracted "miles", i.e, "miles" as seen from the ship? It doesn't make sense if we use "a mile" defined by earth's frame, as it originated, as the standard of length. Edit: Gone for the weekend. Carry on.

First, on the mechanics of light pushing on things... say on a solar sail just to keep it simple: How does the energy of its momentum transfer force to the sail with no mass to push against the matter of the sail? The sail absorbs the light, no doubt, but how does the "push" manifest? As to "distance": I said that the distance between buoys must be 186,000 in earth miles, not contracted "miles" as measured from the speeding ship... requiring the adjustment to compensate as already discussed. Also I already specified that there is, as you said "a difference of 5,580,000 miles between the light and the ship, because one moved at c and one moved at c/2." I laid that out already. Do you have a point in repeating it all? The question remains, why are there only 5,580,000 earth-frame miles between the ship and the far end of the light beam if the light traveled at 'c' ahead relative to the ship as well as relative to the buoys during that minute?

I know that light does not "rest" to be measured as resting mass and that its momentum acts like mass. My question is, how does the energy/momentum of photons "impact" or apply force to objects without a "substantial" agent or carrier of that force, i.e., without mass. I really don't understand how momentum sans mass acts as a force "pushing" on things as in the OP examples. I know and have been referring to that fact. Check. Also already known. I am not arguing for classical physics. See above reply to iNow for my continuing inquiry about how momentum transfers energy and force ("push") as in my examples. I also already know that clocks slow down in rate of "timekeeping" as they move faster or experience stronger gravity and that lengths/distances appear contracted from higher velocity frames. We need not go over all that again. It's my inquiry and I'll tell you what my issue is. I am not interested in how the string of buoys *appears* to the moving ship. The ship would have used its SR manual and computers to adjust for its clock running slower than earth clocks and for the apparent length contraction (to .866/1 if you figure is correct) it experiences because of that while dropping the buoys. But its mission was to place the buoys 186,000 earth-based miles apart... not length-contracted "miles" as "seen" from the ship's high velocity. I have no argument with what DH said about that as per "in the frame of the ship.": Also no argument with the rest of that post and all the math. My thought experiment specified earth miles as the units between buoys. The question then remains regarding the distance between the ship and the end of the light beam (5,580,000 earth-frame miles) after a minute of travel. I agree with Spyman here: My setup was meant to illustrate the example as seen from earth's frame of reference, assuming that the whole operation (both ships) were earth-based at launch and that their 1/2 'c' velocity was relative to earth... not about creating an alternative reality "as seen from the ships' frame of reference."... again, not disputing the observations as seen from the ships.

I was obviously using the earth standard mile as derived from earth's frame. That is what "a mile" means. So the ship that dropped the buoys would have used that standard for the distances between buoys, once 'fixed' in place. Of course the ship would have compensated for its 1/2 'c' velocity and the resulting .866 apparent contraction of distance between drops. I was striving to demonstrate how the whole example would 'pan out' in old fashioned earth miles marked out over the course of the travel through space in question. Another part of the photon "pushing" issue raised in the OP was raised again in post 4. I redirect attention to the above and ask again.

So now my OP questions are ignored and the thread has gone into off-topic chatter. I would call it "thread hijacking" but I don't like the label, having been accused of it so much myself. Thanks DH for making it personal and then derailing it onto a sidetrack.

Right. I misspoke, which should have been obvious by the context of the ship and its light beam passing the buoys. The buoys were meant to represent 'mileposts' on the 'road through space' traveled by the ship. So, to be accurate, the ship which dropped the buoys, if it were going at half 'c' also would have programmed their retro-rockets to "brake", decreasing velocity relative to the ship until they each had lost 1/2 'c' of velocity. OK? Now, again, "what am I missing" given that there are only 5,580,000 miles between the ship and the front end of the light beam after a minute of travel?

Thanks for all your answers. As I said in the OP, "I don't know. Just asking." My "guess" must have been wrong about flying into the projected beam absorbing the ships velocity... as a guess why there is no cumulative velocity. A case of "fuzzy" thinking. You are right. Once light is projected ahead, the ship will never catch up with it, let alone travel into it. Which leaves the mystery as stated, i.e., why is the beam not boosted to 1&1/2 'c'? Clearly light can not be "pushed" faster than 'c', so what happens to the ship's velocity? I still don't know. But I'm working on it. The "velocity relative to what?" question (in lieu of no "aether") can be answered by adding some props along the direction of travel. Say some space buoys had been placed along the way, brought to rest (zero velocity) relative to the approaching ship. Say they are placed every 186,000 miles, to make it easy. The ship's light beam passes one every second, while the ship, at 1/2 'c', passes one every two seconds. After a minute the ship will have passed 30 buoys (having gone 5,580,000 miles) and its beam will have passed 60 of them (having gone 11,160,000 miles.) Then the distance between the ship and the far end of the beam is 5,580,000 miles, yet the light traveled 11,160,000 miles. What am I missing here?

If the ship sent out a pulse of light, your first statement would remain true. Even a single photon pulse would be gone. But I already "imagined" and suggested a steady beam being shone ahead, as in your second example. You then say, "There is still no interaction. There is no traveling into the beam of light. It doesn't make sense." Am I to take this on your authority or because of your lack of making sense of it or do you have an argument against my assumption? As a steady beam projected ahead at 'c' from a ship traveling at 1/2 'c', we know that the beam remains constant at 'c'. One explanation of the fact that the velocities are not cumulative is that the ship is traveling into the beam it is projecting. Rather than just saying 'not so' how about explaining how it can not be so? That photon travels at 'c' too. 'C' remains constant regardless of the velocity of the light source... in any direction (and also independent of any other observational frame of reference.) So please address my inquiry as stated ... or quit the thread if it's just another lecture on constant 'c.'

Most of my questions are still left unanswered. But I will go with what you did say above. I don't think that the forces will be equal in magnitude. My question was about pushing vs being pushed. The velocity of the approaching mirror will effect how much it pushes on the reflected light. But we know that the light has the momentum of lightspeed. Its pushing on the mirror will probably dwarf the force of the mirror, at whatever sub-light speed, “pushing” on the light beam. I don’t know if light can be pushed, however trivially... not yet measured. That’s why I asked the question. My reply to this post just disappeared. Who knows why? I will write it again. My bullet example assumed no such thing. It was an example of physics demonstrating the contrast with constant 'c', as I said already. Is the first statement above just your opinion or do you have a reasoned argument to back it up? As I said, I was positing a constant light emission, not a pulse of photons which are then "gone.' "Travel into the tail end of that light? What does that mean." It means that the light which the ship is shining ahead is traveling at 'c' no matter how fast the ship is traveling. So if it is going 1/2 'c', the reason that the beam is not boosted to 1&1/2 'c' is that the ship is traveling into the beam at 1/2 'c.' There is nothing intentionally hidden here. I am not "assuming there is some absolute frame of reference in which an object's true velocity can be specified." We all know that velocity is always relative to whatever it is measured in reference to. (See all of the above.) This seems to derail the topic. My questions remain unanswered.

Could we please leave Newton (and the history of science) out if for the moment as we discuss the topic here as per the inquiry. My "bullet" example was intended to contrast cumulative velocity with the established fact that constant 'c' requires that there is no cumulative velocity for light shone ahead from a high speed ship. What is wrong with my guess as to why not? Please don't make it personal.

I see. The velocity of the approaching mirror gives reflected light more energy and momentum without more speed. But I'm not sure how that constitutes a "push." Maybe its just that "push" is not a specific enough scientific term. It's obvious with a bullet fired ahead from a moving gun, "pushing" it to its regular velocity plus the gun's velocity. But, of course that doesn't work for a light shone ahead of a high speed ship, as above. In that case it must be, as I said, "... that the ship must travel into the tail end of that light, absorbing the difference between its velocity and 'c.' Yes? In the 'box of mirrors' experiment, the light is clearly "pushing" against the mirrors inside the box. It is hard to see how the mirror above reverses that, i.e., how does its velocity reverse the physics of what is pushing against what? I'm still not clear on the concept. Surely there is mutual "pushing" in that case, light against mirror and mirror against light. No? How is the above situation different than light "pushing" against a laser gun as in laser recoil when fired? Certainly the light is "interacting" with (pushing against) the gun... why not with the ship? (I'm talking a steady beam here, not just a single pulse, to be clear.) Edit; Ps: In all possible cases of light pushing or being pushed, the question for me still remains, "How is it that mass-less light act like mass? Or, "how does mass-less momentum "push" at all with no 'substance' (so to speak) to impact whatever it pushes on?"

This question has bugged me for a long time. Sunlight "pushes" against 'solar sails.' They call it "solar wind." Laser light "pushes" against the lasers which fire it. They call it laser recoil. Light trapped in a box of mirrors "pushes" against the inside of the box, giving it more static inertia as if it were added mass. Yet the classic thought-experimental spaceship traveling at a significant fraction of lightspeed can not "push" a light shining ahead any faster than its speed limit, 'c.' It seems that the ship must travel into the tail end of that light, absorbing the difference between its velocity and 'c.' And it seems that its momentum acts like mass traveling past massive objects. I don't know. Just asking.

michel12345, I am sorry if you feel that I hijacked your thread. (Do you?) I will not reply in this thread again. My last post was a direct reply to md's argument, point by point.

md: "You say "No." Please explain." (Reply to 18 below) I did already in different ways in every post... 2, 9, 11, etc. 11: "If time is just the concept of that which elapses as things move, that can be longer or shorter duration depending on the physical process involved (and velocity/gravity situation for a clock.)" 13: "It's not like clocks detect and measure something called "time" which slows down. It is simply that clocks slow down." 18: "Title: "Change and time... can change happen without time?" No. Change is movement on whatever scale, whatever the event or events. Movement takes time. Whether movement happens faster or slower is another question, depending on a wide variety of factors." md, 20: It is not a personal definition. It seems to me the most generic/universal meaning of time, as above: “... time is just the concept of 'that which elapses' as things move,.” (not a thing/entity.) “A year” of time elapsed in 2002. “A year” (about the same duration) will have elapsed in 2012. There is your “ordering” of different timed events with same duration but happening “at different times.” Regarding time and all the confusion around it, simple is better as long as it makes sense and describes “event duration” in the observable world without trying to "make something of it" (reify it.) Regarding your example: I don’t see any reality to the concept of t=0. This is based on linear thinking cosmology (like "in the beginning"), with which I disagree.(I prefer infinitely ongoing cyclical.)Your example requires that, first there is nothing... then something (magically appearing)... and its movement (change) begins time. No. Also no "end of time."

Please elaborate on your opinion that the JCS is an example of "philosophy badly practiced." Thanks.