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But why, why would this change the past? Let's say you've a magical superluminal laser. The laser is turned on 20 lightyears away now, you see the dot appear

But why, why would this change the past? Let's say you've a magical superluminal laser. The laser is turned on 20 lightyears away now, you see the dot appear immediately, instead of 20 years later (because it was magically superluminal). But of course no laser dot would appear before the other side turned on the laser. Wouldn't the recording just show the same thing over and over again?

BizarroLand 5y ago
My assumption would be that the laser would move into the past at the same speed that we move into the future, so that might be the issue. If that were the case, each moment of the future would be further changed by the, (I don't know if this is the correct term but it seems appropriate) "temporally equidistant" moment in the past. If that were the case, eventually the recording of the laser dot would not show a laser dot at all as the laser dot would have been fired before the video was recorded. In the case of your magical superluminal laser, from your perspective what would happen is that it would show up and then appear to retreat at light speed back to its source 20 years later, right? But that's magic. If a laser actually traveled backwards in time then it would continue to do so until it ceased traveling backwards in time, so each moment forward would be a moment where the past was changed a little bit more by the equal backwards movement in time.
- BizarroLand 5y ago
  Another interesting thought that just crossed my mind is this: Suppose you have a magical superluminal laser. Whatever you point it at (with a direct line of sight), no matter how far away, will be lit up with the laser at the moment you push the button. That laser beam will appear at the location you pointed it however many light years in the past it would have taken for light to travel to its destination and then return over time to the moment you fired the laser. From the moment your superluminal laser is operational and verified to be working, how many alternate timelines are collapsing out of probability every moment you either are or are not pushing the button? If you push the button, you instantly change the past, right? The universe suddenly becomes a universe where a laser, that from the local time observers viewpoint, suddenly appeared out of nowhere and then flew off at the speed of light to your location. The change may be minuscule (a 5mw red laser light touching on the surface of the moon with no observer is such a small variation as to be essentially negligible in the grand scheme of things after all) but it could also be massive. For instance, lasers have a radius that they spread out from over a distance. No laser is perfectly uniform that we are currently capable of creating. This laser collimation problem is well known and apparently impossible to correct for. So, there are 2 ways this could go. If it worked the exact same way forwards as backwards, then no big deal, a few photons from 20 light years away seem to appear out of nothing and zip away. But if this magical laser fires and arrives 20 years in the past with its starting intensity, then that creates some problems. In the first probability, the laser light will then fly back and begin dispersing normally, spreading out across its arc radius as it reverses to its source and then somehow the massive, multi-light year spread of light all converges simultaneously at the moment the button is pushed (this is the good ending), or alternatively, the amount of energy needed to arrive collimated at the destination is enormous, and since nature abhors a vacuum the universe will provide the needed energy, the laser drawing more and more energy in during the return trip to account for the arc difference over the distance. If the former happens, that will be an interesting thing to see as light moves at truly infinite speeds for the moment immediately before the button is pushed. Poof! Magic, no harm, no foul. If the latter happens, then things get really funky. If you fired a 1 watt laser 20 light years away, then the laser will have to travel 300,000,000m/s * 31557600 light-seconds * 20 = 18,934,560,000,000,000,000,000 meters, or roughly 19 sextillion meters (for simplicity). Lasers spread out by a multiplier of roughly 1x per meter of distance. So the laser that arrived in the past at 1 watt would have necessarily required 19 sextillion watts of power. The most powerful laser in the world hasn't even been built yet but is estimated to be able to draw 100 petawatts of power, or 1^17. Your laser would be 1.89^22, or 5 orders of magnitude more powerful than that. It would start out arriving harmlessly at its destination, probably bright enough to stun someones eyes, and then begin a light speed return trip through normal time back towards its source, increasing its power with every second on its way back until, at the infinite moment right before the button was pushed arriving at its destination with nearly 2,000,000 times the amount of energy produced by the entire planet's electrical grid all focused on a single point. Needless to say, some very interesting things might happen should you ever push that trigger. It is difficult to imagine what those things would be but I'm guessing if all you got was a gigantic explosion that might be all for the best. That much energy density in such an infinitely small location might be enough to destroy the city, or the continent, or wipe out all life on the planet, or possibly jump start the second big bang. I don't have enough knowledge to know for certain, but your magical laser might possibly be the death of the universe. For every moment that you do not push the button, potential timelines of existence flare out of the range of possibility. But the moment you do push the button, you potentially create an entirely new timeline where an insanely powerful and unstoppable force of nature began hurtling at the speed of light towards a very specific destination, ultimately destroying everything in its inexorable path, a tidal wave of energy, a laser tsunami crashing towards a lens operated by the tip of your finger. All I can say is that thank God you didn't point it at Betelgeuse (642.5 light years away)
  - jnurmine 5y ago
    I have to admit I still fail to understand why the laser would somehow travel to the past. > That laser beam will appear at the location you pointed it however many light years in the past it would have taken for light to travel to its destination and then return over time to the moment you fired the laser. No... I mean, you'd be able to see the laser button being pushed 20 years later (assuming 20 LY distance), but the laser light appears before this (because it was magical superluminal laser with polarized hull plating and photons that travel 20 LY in a second, or such). This doesn't mean the laser push has not happened at the moment when the laser dot appears. It has. This is why you see the dot. Far away someone must have pushed the button at this very instant. You just haven't observed the push yet because of the large distance (and speed of light slower than the magical superluminal laser).
    - BizarroLand 5y ago
      Either way you look at it you're involving time travel through the normal universe. For someone 20 light years away to click a button and a laser appear at a spot next to you simultaneously. I mean, whew. There's so many things that have to be accounted for that it boggles the mind. 1. The universe is spinning. 2. The galaxy is spinning 3. The solar system is spinning 4. The planet is spinning. All together you are moving hundreds of thousands of miles an hour. Over 20 years that's trillions upon trillions of miles. This laser would have to compensate for the universal drift of 2 points nineteen sextillion meters apart over the course of 20 years. That's aside from the point. We are dealing with things that are faster than the speed of spacetime. (space is time, time is space) So, what would happen is you would click the button, and the laser would arrive at its intended destination 20 light years away simultaneously. Then, the universe will start to catch up to the lasers pre-afterimage. (I can't think of a better term for this, I'll try to explain. You're with the laser at Point A. Destination is Point C. The Point B is the space and time between Point A and Point C. After the laser instantly jumps from Point A to Point C, the universe must still inexorably traverse Point B, during which it will encounter, in its future, the past afterimages of your laser, a.k.a its pre-afterimage.) That is what I mean by the laser traveling into the past. Even though it's the same point in relative time between Point A and Point C, the laser, assuming that it is following some version of universal law, must still traverse the distance between the two points. If it did it faster than the universe can, that's fine, the universe will still commute that time distance either way. From the point of view of Point C, the laser will appear and then recess back towards Point A over the course of the next 20 years. (This has to happen because the universe moves at the speed of light even if something else within it did not). From the point of view of Point A, 20 years ago a laser of some intensity was fired at it and hit it the moment the button was pushed. Both of these things are true because the speed of light was broken by your magical laser. During the universe's commuting of that time distance, interesting things will happen. When I was talking about the laser tsunami (and thank you for creating an opportunity for me to earnestly write the phrase "laser tsunami" twice in my lifetime) that is talking about what must inexorably happen on the other side of Point A or Point C temporally. For Point C, not much, a little flash of light. For Point A, either some really pretty light shows or total universal destruction. Sure, whatever. But no matter how fast the laser moved, the universe must still cross the length of Point B, and as it does so (since we are moving in linear time) the universe will experience either essentially negligible effects (in the case of the 2 happier endings I presupposed in my last post) or it will undergo catastrophic alterations as it reacts to more energy than exists within itself ripping across 20 light years of distance in an infinitely short amount of time. Light doesn't have mass but it does have energy. Energy is mass. That will have an effect on the universe whether you want it to or not. Space and time are the same thing. 20 light years of distance is therefore 20 years of temporal distance at least from the inside of this universe. Point C by all accounts must therefore be 20 years in the past from Point A in order for a laser from Point A to hit Point C at the time the laser is fired from Point A. This is despite the fact that they are currently at the same time frame in the temporal view. (That means that when you have a faster than light anything, everything that it can reach at faster than light speeds must be in the past even though they are both now). If it wasn't, you would miss the shot because where you pointed the laser on Point C would be where Point C was 20 years ago, hundreds of trillions of miles away from where it would be right now.

BizarroLand 5y ago

My assumption would be that the laser would move into the past at the same speed that we move into the future, so that might be the issue. If that were the case, each moment of the future would be further changed by the, (I don't know if this is the correct term but it seems appropriate) "temporally equidistant" moment in the past. If that were the case, eventually the recording of the laser dot would not show a laser dot at all as the laser dot would have been fired before the video was recorded. In the case of your magical superluminal laser, from your perspective what would happen is that it would show up and then appear to retreat at light speed back to its source 20 years later, right? But that's magic. If a laser actually traveled backwards in time then it would continue to do so until it ceased traveling backwards in time, so each moment forward would be a moment where the past was changed a little bit more by the equal backwards movement in time.

BizarroLand 5y ago
Another interesting thought that just crossed my mind is this: Suppose you have a magical superluminal laser. Whatever you point it at (with a direct line of sight), no matter how far away, will be lit up with the laser at the moment you push the button. That laser beam will appear at the location you pointed it however many light years in the past it would have taken for light to travel to its destination and then return over time to the moment you fired the laser. From the moment your superluminal laser is operational and verified to be working, how many alternate timelines are collapsing out of probability every moment you either are or are not pushing the button? If you push the button, you instantly change the past, right? The universe suddenly becomes a universe where a laser, that from the local time observers viewpoint, suddenly appeared out of nowhere and then flew off at the speed of light to your location. The change may be minuscule (a 5mw red laser light touching on the surface of the moon with no observer is such a small variation as to be essentially negligible in the grand scheme of things after all) but it could also be massive. For instance, lasers have a radius that they spread out from over a distance. No laser is perfectly uniform that we are currently capable of creating. This laser collimation problem is well known and apparently impossible to correct for. So, there are 2 ways this could go. If it worked the exact same way forwards as backwards, then no big deal, a few photons from 20 light years away seem to appear out of nothing and zip away. But if this magical laser fires and arrives 20 years in the past with its starting intensity, then that creates some problems. In the first probability, the laser light will then fly back and begin dispersing normally, spreading out across its arc radius as it reverses to its source and then somehow the massive, multi-light year spread of light all converges simultaneously at the moment the button is pushed (this is the good ending), or alternatively, the amount of energy needed to arrive collimated at the destination is enormous, and since nature abhors a vacuum the universe will provide the needed energy, the laser drawing more and more energy in during the return trip to account for the arc difference over the distance. If the former happens, that will be an interesting thing to see as light moves at truly infinite speeds for the moment immediately before the button is pushed. Poof! Magic, no harm, no foul. If the latter happens, then things get really funky. If you fired a 1 watt laser 20 light years away, then the laser will have to travel 300,000,000m/s * 31557600 light-seconds * 20 = 18,934,560,000,000,000,000,000 meters, or roughly 19 sextillion meters (for simplicity). Lasers spread out by a multiplier of roughly 1x per meter of distance. So the laser that arrived in the past at 1 watt would have necessarily required 19 sextillion watts of power. The most powerful laser in the world hasn't even been built yet but is estimated to be able to draw 100 petawatts of power, or 1^17. Your laser would be 1.89^22, or 5 orders of magnitude more powerful than that. It would start out arriving harmlessly at its destination, probably bright enough to stun someones eyes, and then begin a light speed return trip through normal time back towards its source, increasing its power with every second on its way back until, at the infinite moment right before the button was pushed arriving at its destination with nearly 2,000,000 times the amount of energy produced by the entire planet's electrical grid all focused on a single point. Needless to say, some very interesting things might happen should you ever push that trigger. It is difficult to imagine what those things would be but I'm guessing if all you got was a gigantic explosion that might be all for the best. That much energy density in such an infinitely small location might be enough to destroy the city, or the continent, or wipe out all life on the planet, or possibly jump start the second big bang. I don't have enough knowledge to know for certain, but your magical laser might possibly be the death of the universe. For every moment that you do not push the button, potential timelines of existence flare out of the range of possibility. But the moment you do push the button, you potentially create an entirely new timeline where an insanely powerful and unstoppable force of nature began hurtling at the speed of light towards a very specific destination, ultimately destroying everything in its inexorable path, a tidal wave of energy, a laser tsunami crashing towards a lens operated by the tip of your finger. All I can say is that thank God you didn't point it at Betelgeuse (642.5 light years away)
- jnurmine 5y ago
  I have to admit I still fail to understand why the laser would somehow travel to the past. > That laser beam will appear at the location you pointed it however many light years in the past it would have taken for light to travel to its destination and then return over time to the moment you fired the laser. No... I mean, you'd be able to see the laser button being pushed 20 years later (assuming 20 LY distance), but the laser light appears before this (because it was magical superluminal laser with polarized hull plating and photons that travel 20 LY in a second, or such). This doesn't mean the laser push has not happened at the moment when the laser dot appears. It has. This is why you see the dot. Far away someone must have pushed the button at this very instant. You just haven't observed the push yet because of the large distance (and speed of light slower than the magical superluminal laser).
  - BizarroLand 5y ago
    Either way you look at it you're involving time travel through the normal universe. For someone 20 light years away to click a button and a laser appear at a spot next to you simultaneously. I mean, whew. There's so many things that have to be accounted for that it boggles the mind. 1. The universe is spinning. 2. The galaxy is spinning 3. The solar system is spinning 4. The planet is spinning. All together you are moving hundreds of thousands of miles an hour. Over 20 years that's trillions upon trillions of miles. This laser would have to compensate for the universal drift of 2 points nineteen sextillion meters apart over the course of 20 years. That's aside from the point. We are dealing with things that are faster than the speed of spacetime. (space is time, time is space) So, what would happen is you would click the button, and the laser would arrive at its intended destination 20 light years away simultaneously. Then, the universe will start to catch up to the lasers pre-afterimage. (I can't think of a better term for this, I'll try to explain. You're with the laser at Point A. Destination is Point C. The Point B is the space and time between Point A and Point C. After the laser instantly jumps from Point A to Point C, the universe must still inexorably traverse Point B, during which it will encounter, in its future, the past afterimages of your laser, a.k.a its pre-afterimage.) That is what I mean by the laser traveling into the past. Even though it's the same point in relative time between Point A and Point C, the laser, assuming that it is following some version of universal law, must still traverse the distance between the two points. If it did it faster than the universe can, that's fine, the universe will still commute that time distance either way. From the point of view of Point C, the laser will appear and then recess back towards Point A over the course of the next 20 years. (This has to happen because the universe moves at the speed of light even if something else within it did not). From the point of view of Point A, 20 years ago a laser of some intensity was fired at it and hit it the moment the button was pushed. Both of these things are true because the speed of light was broken by your magical laser. During the universe's commuting of that time distance, interesting things will happen. When I was talking about the laser tsunami (and thank you for creating an opportunity for me to earnestly write the phrase "laser tsunami" twice in my lifetime) that is talking about what must inexorably happen on the other side of Point A or Point C temporally. For Point C, not much, a little flash of light. For Point A, either some really pretty light shows or total universal destruction. Sure, whatever. But no matter how fast the laser moved, the universe must still cross the length of Point B, and as it does so (since we are moving in linear time) the universe will experience either essentially negligible effects (in the case of the 2 happier endings I presupposed in my last post) or it will undergo catastrophic alterations as it reacts to more energy than exists within itself ripping across 20 light years of distance in an infinitely short amount of time. Light doesn't have mass but it does have energy. Energy is mass. That will have an effect on the universe whether you want it to or not. Space and time are the same thing. 20 light years of distance is therefore 20 years of temporal distance at least from the inside of this universe. Point C by all accounts must therefore be 20 years in the past from Point A in order for a laser from Point A to hit Point C at the time the laser is fired from Point A. This is despite the fact that they are currently at the same time frame in the temporal view. (That means that when you have a faster than light anything, everything that it can reach at faster than light speeds must be in the past even though they are both now). If it wasn't, you would miss the shot because where you pointed the laser on Point C would be where Point C was 20 years ago, hundreds of trillions of miles away from where it would be right now.