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Everything posted by Janus

  1. The perspective effect is due to the fact that objects of the same size subtend a smaller angle of your visual field as the distance to them increases. If the observer is moving relative to the object, a second visual effect also has to be taken into account: aberration. Aberration affects the angle at which you will see the light coming from. In the case where you are looking at an object coming towards you, the angle tightens inward making the object "look" smaller. So let's go back to my last example: A and B both see light coming from planet X as they pass each other. They see the same light. The difference is that due to aberration, A sees the light come from a smaller angle, and visually "sees" a smaller image. Now this is not inconsistent with what I said about what he concludes, which is that the light he is now seeing left planet X when it was 3 light hrs from him, thus he would expect to "see" a smaller image. The point is that there is nothing about what A "sees" that runs contrary to, or is inconsistent with, what Relativity says is happening. Relativity usually ignores these secondary "visual" effects, not because it can't deal or account for them, but because at best, They don't tell us anything important, and at worst, they add unnecessary "clutter" to the scenario.
  2. We had bad air quality for ~ a week, staying in the "Very unhealthy" to "Hazardous" ranges. We tried to seal things up as best we could, but the smell of smoke still found its way in. We were stuck in a thermal inversion that was holding the smoke near the ground. We finally broke out of it Friday, when a system finally blew in. Had good air quality for a few days, then it jumped back up to over 130 today again, before dropping back to under 100 this evening.
  3. Again A and B would visually "see" the same thing. They would conclude a different state of things. B is at rest with, and 1 light hour from planet X as measured by either. A is moving at 0.8c relative to both, and is passing B on his way to planet X. As A and B pass, they see the same light that came from Planet X. B concludes that the light left 1 hr ago and took one hour to reach him across the 1 light hr distance separating them. A however, has to reason like this: "I am now seeing light from Planet X, while I am next to B, This light was traveling at c relative to me, and had to have left planet X before I was next to B, and when the distance between Planet X and myself was much greater than it is at this moment now, when I am next to B Planet X was 3 light hrs away from me when the light left, to be exact. It took 3 hrs for that light to reach me, during which time, The distance between planet X and myself decreased at 0.8c to 3lh -(3h*0.8c) = 0.6 light hrs. Thus as I am passing B, planet X is 0.6 light hrs from me ( even though the light I am now seeing left it when it was 3 light hrs from me) " A and B see exactly the same light from Planet X as they pass each other, but reach different conclusions as to how far away planet X is at that moment. A can reaffirm his conclusion by waiting until he and planet X meet up, which will occur in 45 min by A's clock. 45 min * .8c = 36 light min = 0.6 light hrs.
  4. Yes, you are wrong. You are again confusing what someone visually "sees", and what they would determine as being true at that moment. He would "see" exactly the same light as he saw before he made the jump* However, the conclusions he would make based on what he sees and his relative velocity to planet X would be that Planet X is closer and length contracted at that moment. It is important to separate the "optical" effects due to Relativistic velocity differences from the actual Relativistic effects. For example while according to you, an object flying by you at .8c would be length contracted, visually you would see it rotating as it passed you. This "Terrell rotation" is an optical effect, which doesn't represent an actual rotation of the object according to you, but the length contraction is measured as a physical change. This distinction between what one "sees" and what they "determine" seems to be something you struggle with. * There would be an aberration effect which would distort the image of planet X for him, But that would occur with or without Relativity( just to a different degree). And this aberration would vanish just as quickly if he were to come to a rest again with respect to Planet X.
  5. As Bufofrog has already pointed out, this would mean that two people, at the same spot and at rest with respect to each other would see two different things happening to the Earth for an hour. This is impossible, as the same light from the Earth is reaching both of them simultaneously at any given moment of that hr. Your claim leads to a physical contradiction.
  6. Or maybe it has something to do with the fact that even without taking relativity into account, even if we had rocket engines 100 time more efficient than the most efficient one presently available, such a rocket would have to mass over 19 times the mass of the Earth, just to get a 1 kg payload up to the speed of light. However, we do have countless practical observations and experiments that do give results that lend support to Einstein's Theory. This is why it is accepted, for the very reason that it has passed every test thrown at it. It would have never gained the level of acceptance it has without such experimental evidence. And science continues to throw tests at it.
  7. No he doesn't. Because, since the traveler has to undergo a change of velocity at the end of his outbound leg in order to return to the Earth, he will see a change in the frequency of light he receives from the Earth when he makes that velocity change. There is no delay. He sees the Earth clock tick at 1/3 speed for 45 min by his clock and thus accumulating 15 min, and then sees it ticking 3 times as fast for 45 min, accumulating 2 hrs, 15 min. Thus he sees the Earth clock accumulate 2 1/2 hrs while his own clock ticked off 1 1/2 hrs. The Earth observer has to wait to see the result of the velocity change because it takes place 1 light hr from him. The traveler doesn't have to wait, because he is the one making the velocity change, so it is happening where he is. I never addressed what the traveler would have seen before this. You jumped to an erroneous conclusion regarding what the traveler would see.
  8. Because If A sees B's clock tick slow while he travels out to a distance of 1 light hour, he will see it ticking slow for 2 and 1/4 hrs and accumulate 45 min of time. He will then see B's clock tick 3 times as fast for 15 min. End result, he sees B's clock accumulate 1 1/2 hrs in the time it takes for his own clock to tick off 2 1/2 hrs. In order to get a result where B's clock ticks off as much as A's, you would need to use the Newtonian equation for Doppler shift, or f0 = fs (c/(1±v/c) Where v is positive if the source is receding. In this case, A would see B's clock tick 5/9 as fast on the outbound trip, accumulating 1 1/4 hrs in 2 1/4 hrs by A's clock, and then tick 5 times faster for 15 min, accumulating another 1 1/4 hrs, for a total of 2 1/2 hrs, the same that accumulates for A. However, this is not what we measure in real life. We measure a Doppler shift that matches the Relativistic version, which ends up giving an answer of less accumulated time for B.
  9. To understand time, you have to understand Relativity, because, at its heart, Relativity is all about the very nature of Time and Space.
  10. And, in the rest frame of clock 3, it is clocks 1 and 2 that are moving at 0.8 c, and thus are length contracted, and this includes the distance between them. Thus by the 3rd clock's measure, the distance between clocks 1 and 2 is only 0.6 lh. So, as it passes clock 1, clock 2 is 0.6 lh away, is coming towards him at 0.8c, and takes 0.6lh/0.8c = 0.75 hr = 45 min.
  11. 1. No, the 3rd clock traveled 1 light hr in 1hr 15 min as measured by you, it just also ran slow by a factor of 0.6 and thus only accumulated 45 min , as measured by you. Visually, you saw it take 2 hr and 15 min to reach that 1 light hr distance. 2. Again, it took the clock 1hr 15 min to travel the distance. The fact that it arrived only 15 min after you saw it start its trip is just because it was following closely behind it's own light. Two cars leave a point 100 miles from you, driving towards you. One car, traveling at 100 mph carries a message that says the other car is also just leaving. The second car travels at 80 mph. The faster car arrives at 1:00, while the second car arrives 15 min later at 1:15. Now just because the message saying that the second car was leaving arrived just 15 min before the second car arrives, this does not mean that you will conclude that the second car only took 15 min to cross the distance and had to be traveling at 400 mph. The second car took 1 hr 15 min to make the trip, it was just following not too far behind the faster car.( By the time the first car arrives, the second car is only 20 miles away) Again, you are conflating "what someone visually sees", with what they say is actually happening. If I am 1 light hour from a clock stationary with respect to me, and see it reading 11:00, I don't think that the clock reads 11:00 at that moment, but that, assuming the clock continued to run, it ticked off an additional hr since the image I am now seeing left it, thus I will say that the clock now reads 12:00. Conversely, if your clock reads 12:00, you know that the light left when your clock read 11:00 and thus both clocks read 11:00 at that moment. This works if even if the other clock is moving relative to you. Light that left it when it was 1 light hr away will carry the image of what that clock read 1 hr ago by your clock. So if your clock reads 2:15 when you see the image of the 3rd clock carried by light that left it when it was 1hr away, You know that image left when your clock read 1:15. and if that image is of the 3rd clock reading 12:45, you know that the 3rd clock read 12:45 at the same moment your clock read 1:15.
  12. The Doppler effect does, but the time dilation does not. The relativistic Doppler shift is due to two compounding effects: Changing light propagation delay due to changing distance, the effect of which is determined whether the propagation delay is increasing or decreasing. Time dilation, which only depends on relative speed and is independent of direction. So with the above example, Doppler shift gives a value of 1/3 on the for the receding leg and 3 for the return leg, but time dilation has a factor of 0.6 for both legs.
  13. Again. Relativistic Doppler effect. (which is what you get by combining both light propagation and time dilation) If the clock is receding at 0.8 c, you see it ticking 1/3 as fast as your own. If it is approaching at 0.8 c, you see it running 3 times faster. One way to look at it is that by the time you visually see that clock begin its return trip, the clock has already been on its return leg for an hr, and only 15 min remain until it arrives. All the light emitted from it during the return leg is squeezed into that 15 min by your clock. If you see the returning clock tick 3 times faster, 3*15 min = 45 min is the time you see pass on that clock during its return leg. If you factor out the light propagation delay you will conclude that the clock left reading 12:45, when your clock read 1:15. It took 1 hr 15 min to cross the 1 light hr at 0.8c, and arrives when your clock reads 2:30. The clock read 12:45 when it left, and reads 1:30 when it arrives, thus ticked off 45 min in that 1 hr 15 min by your clock, or 6/10 of 1 hr 15 min(75 min) The time dilation factor for 0.8c is 0.6.
  14. How is using 1.25 hrs any different than saying 1 and a quarter hrs? or 1 1/4 hrs. The fact that the number is followed by "hrs" indicates that the numerical value is applies to the one unit, hours, while with 1:15 the ":" denotes a marker between units, or 1 hr, 15 min. I'm sorry if this confuses you, but when working with such problems it is easier to the work the math out in decimal hrs and then convert back to Hr and min afterwards if you need to. If the clock left you moving at 0.8c to a point 1 light hr away ( as measured by you), while both it and your clock both read 12:00, then it will take, by your determination, 1 hr 15 min to reach that point. You, however, will not see him arrive when your clock reads 1:15, as It will take an another hr for the light from his arrival to reach you, so you will see the image of his arrival 2 hr and 15 min after he left, when your clock reads 2:15. In other words, you will "see" his entire trip as being stretched out over 2 hrs 15 min. As you watched him recede from you, you will see him via relativistic Doppler shift. This does not only effects the measured frequency of the light you get from him, but also the rate at which you would "see" his clock tick. The Relativistic Doppler shift rate for 0.8c is 1/3. Since you see this happening for the entire 2 hr and 15 min, you will see that clock ticking off only 1/3 of that, or 45 min. Thus when you see the clock arrives at that point 1 light hr away, you will see it as reading 12:45.
  15. Orangutans, gorillas, and chimpanzees were the apes we saw, and were all "greater" apes, while gibbons belong to the "lesser" apes. Maybe the lesser ape species didn't survive. Or maybe they had their own separate communities.
  16. No. The detected frequency would be 1.732 times the source frequency. The red or blue shift is due to a combination of both The changing light propagation times and relativistic time dilation.
  17. If the universe were not expanding, we would not see any red shift with distance. Thus the increasing red-shift we see with increasing distance is evidence that the universe is expanding over time, and was smaller in the past than it is now. If we extrapolate back in time, we get the very dense, very hot state of the Big Bang. The acceleration of the the expansion over time is evidenced by the exact relationship between red-shift and distance. There are three possible scenarios for an expanding universe. All of them will show a red-shift: Case 1: expansion slows over time Case 2: expansion remains constant over time. Case 3: expansion speeds up over time. Only in case 2 will there be a perfect direct relationship between distance and red-shift, where doubling the distance exactly doubles the red-shift. In the other two cases, doubling the distance results in a red-shift that is not an exact doubling. Whether it is less than double or more than double distinguishes between the two cases. We have found that the red-shift distance ratio indicates that the universe's expansion rate has been increasing over time, and thus the rate of the expansion is accelerating.
  18. Galileo would have assumed that light followed the rules of Galilean Relativity and that the speed of the light emitted by B relative to A would depend on the velocity of B relative to A. Thus, if B were traveling away from A at c, its light emitted back towards A would be not moving at all relative to A. If B started at any non-zero distance from A, A would see light coming from it right up to the moment B started moving away at c, and then would see no image of B at all. If B then stops relative to A at a 1 light hr distance*, A would eventually see this two hrs after B left**, If both A and B read 10:00 while near each other, B will read 11:00 when it reaches its destination, and this light will reach A when its reads 12:00. Thus A would see B tick normally up until it starts moving away at c, and then A would see nothing until 12:00, when it would suddenly see B one light hr away and reading 11:00. Knowing that the light took an hour to get to him, that clock B at that moment also reads 12:00. Galileo would assume that clock B just ticked normally the whole time, and there were just portions of the trip that A simply could not see. If B were moving away at greater than c, A would also not be able to see it as it receded, because, once again, the light emitted by B would never get to A (in fact, it would have a velocity away from A.) If B were then were to suddenly reverse direction(for simplicity we'll assume an instantaneous change of velocity) upon reaching 1 light hr from A and returns at c, Galileo would expect A to the see the following. For 1 1/2 hours after B leaves, A sees nothing, Then at 11:30 it will see B at 1 light hr away, reading 11:00 and coming towards A at c. During the next half hr, It will see B close the distance, while B's clock appears to tick twice as fast, accumulating 1 hr of time until both clocks meet with both reading 12:00. If B make the same type of trip at 2c, A sees nothing for 50 min, then at 10:50 B suddenly appears, at a distance of 1 light hr reading 10:30. For the next ten minutes, A sees B close the distance while B's clock ticks 3 times faster, accumulating 30 min, to read 11:00 once it returns to A. In short, Galileo would not assume that anything out of the ordinary happens to Clock B in terms of its tick rate, just that the combination of the SOL and the relative velocity of B to A will alter how the information about B reaches A. And as long as A takes this into account, A will say that clock B always keeps perfect time with clock A Note that this is completely different for Relativity, where A, after taking into account the SOL effects on how the info arrived would conclude that Clock B did not keep time with clock A. Thus in my earlier example, When A sees a 1 hr and 75 sec difference between itself and clock B, 1hr of that is due to light propagation delay, and the remaining 75 sec is due to time dilation that occurred during the outbound trip. *Galileo didn't have a good idea of how fast light traveled, only that it was much faster than sound, so here, we'll just assume some finite value for c. ** This light will pass the stationary(relative to A) light left behind by B on its outbound trip.
  19. He will see whatever time that was on clock B when the light left it. So what? Where are you trying to go with this?
  20. But that is just light propagation delay, which generally is factored out when we deal with SR. Suing your example, with B traveling to a distance of 1 light hr in 1 day: To do this it has to travel at 1/24c. At that speed, the relativistic Doppler shift ( which determines the rate at which A would visually see B tick at as it recedes), is ~0.95917 Since it takes an additional hour for light to travel from a 1 light hr distance, A doesn't see B arrive at the 1 light hr distance until 25 hrs after B leaves. Thus for 25 hrs, A will see B tick at a rate of 0.95917 and accumulate ~86,325 of ~sec, while accumulating 90,000 sec itself. this is a difference of ~ 3675 sec. 3600 of those sec is accounted for by the 1 hr light propagation delay, leaving a 75 sec real time difference. Thus, A, at 10:00, will see B reading 08:58:45, but after accounting for the 1 hr propagation delay, will determine that B actually reads 09:58:15.
  21. It's not enough to just "see" the events simultaneously to say that they were simultaneous, even if you are halfway between the events when you saw them. For the observer to claim that those events were simultaneous, he also would have to have be either stationary with respect to these events or the relative motion between himself and those events would have to be on a line perpendicular to the line joining the events. Another observer moving parallel to that joining line, even if he was at the exact same point as the first observer, and "saw" the events simultaneously, just like the first observer did, would conclude that the events themselves were not simultaneous. So for example, this shows events according to the observer at rest with respect to the events. The white expanding circles is the light produced by the events For him, the events occur simultaneously. Both light flashes and the railway car observer arrive at his position at the same time. However, for the railway observer, the order for the same events is different: The light from both flashes meet at his position at the same moment as he is adjacent to the track observer, but the events producing those flashes did not occur at the same time. This is because he must measure light as traveling at c relative to himself. In other words if he were to measure the speed of either light flash as it passed him, he would measure both as moving a at relative to himself. Thus for him, the light flashes, once emitted, expand outward from the point of emission at c. (the red dots move away from these points, but we don't care what they do after the flashes are emitted) Now for him, the time it takes for a flash to reach him from either event is equal to the distance between him and the event at the moment the event took place divided by c Since the events have to occur prior to his seeing the light flashes, they had to occur before he was at the halfway point between them. He had to be closer to one event than he was the other. Different distances means different travel times at c, and therefore when he sees both flashes at the same time, he also knows that one of those flashes had to travel a longer distance and take a longer time to reach him, and ergo, the events producing those flashes could not have occurred simultaneously.
  22. The reddening we see with the setting Sun is due to the blue end of the spectrum being scattered. Thus the light coming from the direction of the Sun has less Blue light and looks redder. The red-shft we see from distant galaxies cannot be due to a like effect. We measure red-shift by looking at the light's spectrum. In it are patterns of lines that are like "fingerprints" for elements. Each pattern isn't only unique, but it is produced in a certain point of the spectrum. If the red-shift was due to a scattering out of blue light, all you would see would be a dimming in the blue end of the spectrum. The spectral lines would still be there and in the same place. This is not what we see. Instead we see a shift of the whole spectrum towards the red. Spectral lines have moved further to the red end of the spectrum. The wavelength of the light itself has been changed, rather than just certain frequencies filtered out leaving redder light behind. (in fact, red-shifting will shift non-visible frequency ultraviolet into the visible light range.)
  23. No. We used to think that "space" and "time" where unrelated. But then we learned that they are just two ways of measuring the same thing. The term space-time was coined to reflect this revelation. The "illusion" was that time and space were distinct and unrelated.
  24. Well, his 2nd marriage was to his cousin.
  25. No, it's just relative.
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