michel123456 Posted November 22, 2014 Share Posted November 22, 2014 This is a question: Suppose that I am looking in my telescope to a distant star 1 million light years away. Around this star is a planet. On this planet I see an alien observatory and an alien scientist looking in my direction. Can he see me? Link to comment Share on other sites More sharing options...
Strange Posted November 22, 2014 Share Posted November 22, 2014 This is a question: Suppose that I am looking in my telescope to a distant star 1 million light years away. Around this star is a planet. On this planet I see an alien observatory and an alien scientist looking in my direction. Can he see me? No. He was there 1 million years ago. He is probably long dead (depending on the lifespan of these aliens). What he sees is the Earth as it was 2 million years ago. Link to comment Share on other sites More sharing options...
davidivad Posted November 22, 2014 Share Posted November 22, 2014 light is manipulatable to quite a degree. i will go the other way for arguments sake and say that it depends on the configuration of the medium. if a civilization lives within a long enough time frame they have the capability to take advantage of it. Link to comment Share on other sites More sharing options...
Strange Posted November 22, 2014 Share Posted November 22, 2014 i will go the other way for arguments sake and say that it depends on the configuration of the medium. What medium? You are proposing a technology to make light travel instantaneously in both directions? Link to comment Share on other sites More sharing options...
michel123456 Posted November 22, 2014 Author Share Posted November 22, 2014 No. He was there 1 million years ago. He is probably long dead (depending on the lifespan of these aliens).OK I can understand that. Agree. What he sees is the Earth as it was 2 million years ago.This part of your answer is based on our current understanding of time. Does that mean that by any means (gravity & EM radiations), the interactions are delayed? I mean we are receiving EM radiation from this planet today, and this planet is NOT receiving EM from us now, but from the Earth as it was 2 million years from now ? Link to comment Share on other sites More sharing options...
Strange Posted November 22, 2014 Share Posted November 22, 2014 This part of your answer is based on our current understanding of time. All parts of the answer are. I could make one up that isn't based on what we know about time, space and the speed of light (if you prefer)... Does that mean that by any means (gravity & EM radiations), the interactions are delayed? Yes. Because (as far as we know, currently) nothing can transmit information faster than light. I mean we are receiving EM radiation from this planet today, and this planet is NOT receiving EM from us now, but from the Earth as it was 2 million years from now ? Actually, now it is receiving light from the Earth as it was 1 million years ago. (There are obviously, some difficulties defining exactly what "now" means for such widely separated observers. But nothing that is significant to 1 million years.) Link to comment Share on other sites More sharing options...
michel123456 Posted November 22, 2014 Author Share Posted November 22, 2014 (edited) All parts of the answer are. I could make one up that isn't based on what we know about time, space and the speed of light (if you prefer)... Yes. Because (as far as we know, currently) nothing can transmit information faster than light. Actually, now it is receiving light from the Earth as it was 1 million years ago. (There are obviously, some difficulties defining exactly what "now" means for such widely separated observers. But nothing that is significant to 1 million years.) IOW, correct me if i am wrong, what we call "interaction" is not exactly an "interaction" between 2 objects, it is a triangle connecting (to make it simple) A the observer, B the observed object and C the observer "as it was in the past". And when we speak about "interaction" we suppose that A and C are the same objects. Edited November 22, 2014 by michel123456 Link to comment Share on other sites More sharing options...
Strange Posted November 22, 2014 Share Posted November 22, 2014 IOW, correct me if i am wrong, what we call "interaction" is not exactly an "interaction" between 2 objects, it is a triangle connecting (to make it simple) A the observer, B the observed object and C the observer "as it was in the past". And when we speak about "interaction" we suppose that A and C are the same objects. Sorry, I don't know what you mean. What sort of interaction are you talking about? Link to comment Share on other sites More sharing options...
davidivad Posted November 22, 2014 Share Posted November 22, 2014 i would suggest bridge created by someone who has traveld the full dimensions of the experiment. Link to comment Share on other sites More sharing options...
michel123456 Posted November 22, 2014 Author Share Posted November 22, 2014 (edited) Sorry, I don't know what you mean. What sort of interaction are you talking about? Physical interaction. In this case gravitational and electromagnetic. What is troubling me is this: We are traveling in the universe together with planet B, that we observe 1 million LY away and 1 million years in the past. There is no physical way (no bridge) to go to planet B and check what the observer there was looking at . All the travels that we can do are limited by the speed of light. IOW we suppose that the observer there was in the universe with the company of a younger Earth. Respectively, today we may be observed by future astronomers looking at us in their telescopes from distant planets. We cannot see them, but we suppose that they will be on one of those planets we observe today. Again, it is a supposition, there is no physical way to prove that. Those suppositions are based on the way we picture ourselves how time works. It may be correct but it may be wrong, we cannot check. Edited November 22, 2014 by michel123456 Link to comment Share on other sites More sharing options...
Strange Posted November 22, 2014 Share Posted November 22, 2014 Any gravitational or electromagnetic interactions at those distance are going to be negligible. But they will still take place at the speed of light. Link to comment Share on other sites More sharing options...
pzkpfw Posted November 22, 2014 Share Posted November 22, 2014 Physical interaction. In this case gravitational and electromagnetic. That page doesn't list magic. Nothing known will change the speed of light and the distance to your alien. Was this really a question or a sneaky speculation? Link to comment Share on other sites More sharing options...
Strange Posted November 22, 2014 Share Posted November 22, 2014 Those suppositions are based on the way we picture ourselves how time works. It may be correct but it may be wrong, we cannot check. The only supposition is the aliens you have invented. There is no supposition about the speed of light. Not even about it being the same a million years ago and a million light years away. We can actually test such ideas, you know. Link to comment Share on other sites More sharing options...
swansont Posted November 22, 2014 Share Posted November 22, 2014 Those suppositions are based on the way we picture ourselves how time works. It may be correct but it may be wrong, we cannot check. Sure we can. We can look at light coming to us and make sure it follows the laws of physics. Different physics would give different answers, but we see what we should given the physics we know. Link to comment Share on other sites More sharing options...
michel123456 Posted November 22, 2014 Author Share Posted November 22, 2014 (edited) That page doesn't list magic. Nothing known will change the speed of light and the distance to your alien. Was this really a question or a sneaky speculation? I don't question the speed of light. The question is: when I look at the (speculated) alien, does he see me? The answer is : No. The next question is: what is he looking at? Strange's answer is: he is looking (he was looking) at the Earth as it was 2 million years ago. I am questionning Strange's answer. I say: how can we check that? Edited November 22, 2014 by michel123456 Link to comment Share on other sites More sharing options...
John Cuthber Posted November 22, 2014 Share Posted November 22, 2014 I don't question the speed of light. The question is: when I look at the (speculated) alien, does he see me? The answer is : No. The next question is: what is he looking at? Strange's answer is: he is looking (he was looking) at the Earth as it was 2 million years ago. I am questionning Strange's answer. I say: how can we check that? Easy, we can check it in the ;lab. OK you would need a rather large lab to do the experiment on the million year scale, but it's easy these days to measure propagation delays as we bounce em signals round satellites or reflect light from the Moon. Link to comment Share on other sites More sharing options...
swansont Posted November 22, 2014 Share Posted November 22, 2014 I don't question the speed of light. … I am questionning Strange's answer. I say: how can we check that? We check the speed of light, which you are not questioning. Link to comment Share on other sites More sharing options...
michel123456 Posted November 22, 2014 Author Share Posted November 22, 2014 Easy, we can check it in the ;lab. OK you would need a rather large lab to do the experiment on the million year scale, but it's easy these days to measure propagation delays as we bounce em signals round satellites or reflect light from the Moon. How do we reflect light from the Moon? There is an approximate 2 sec gap with the Moon. That means 4 sec to go forth and back. During those 4 sec the Earth & Moon have moved respectively. How do we catch back the signal? from another location? Link to comment Share on other sites More sharing options...
Strange Posted November 22, 2014 Share Posted November 22, 2014 Strange's answer is: he is looking (he was looking) at the Earth as it was 2 million years ago. I am questionning Strange's answer. I say: how can we check that? You invented him, only you know what he is looking at. I gave you an answer based on science. Maybe he is looking at unicorns swarming round the Pleiades. How do we reflect light from the Moon? There is an approximate 2 sec gap with the Moon. That means 4 sec to go forth and back. During those 4 sec the Earth & Moon have moved respectively. How do we catch back the signal? from another location? http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment Link to comment Share on other sites More sharing options...
Robittybob1 Posted November 22, 2014 Share Posted November 22, 2014 (edited) How do we reflect light from the Moon? There is an approximate 2 sec gap with the Moon. That means 4 sec to go forth and back. During those 4 sec the Earth & Moon have moved respectively. How do we catch back the signal? from another location? It is 1 second there and 1 second back (total time approx 2.5 seconds). The Earth and the Moon are rotating around in the same direction with the same side always facing the Earth. So the amount of movement is still little enough for the reflection to work. Edited November 22, 2014 by Robittybob1 Link to comment Share on other sites More sharing options...
michel123456 Posted November 22, 2014 Author Share Posted November 22, 2014 It is 1 second there and 1 second back (total time approx 2.5 seconds). The Earth and the Moon are rotating around in the same direction with the same side always facing the Earth. So the amount of movement is still little enough for the reflection to work. So the Moon & Earth are almost acting like a single object. I see also that the reflectors on the Moon are not parallel to the surface (they are not horizontal on the Moon) http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment#mediaviewer/File:ALSEP_AS14-67-9386.jpg http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment#mediaviewer/File:Apollo_11_Lunar_Laser_Ranging_Experiment.jpg Link to comment Share on other sites More sharing options...
Janus Posted November 22, 2014 Share Posted November 22, 2014 How do we reflect light from the Moon? There is an approximate 2 sec gap with the Moon. That means 4 sec to go forth and back. During those 4 sec the Earth & Moon have moved respectively. How do we catch back the signal? from another location? If we want to hit a reflector on the Moon we have to take into account both the light time delay and the 1km/sec orbital velocity of the moon. It takes ~1.25 sec for light to travel from Moon to Earth, so the light we see is 1.25 sec old, which means the Moon has moved ~1.25 km in the time it took for its image to reach us. It will also take ~1.25 sec for laser we fired to hit the Moon, during which time the Moon has moved an additional ~1.25 km. Assuming we are aiming at a reflector that is fairly small, we aim our laser ~2.5 km ahead of where we see the reflector. Now, it will take ~2.5 sec for the laser to make the round trip, during which time the image of the Moon we see in the sky moves ~2.5 km. Since we "lead" the reflector by ~2.5 km when we fired the laser, the image carrying the refection will have moved exactly to the spot where we aimed the laser. IOW, the reflection we see comes back from the same direction as we aimed the laser. 3 Link to comment Share on other sites More sharing options...
Robittybob1 Posted November 22, 2014 Share Posted November 22, 2014 So the Moon & Earth are almost acting like a single object. I see also that the reflectors on the Moon are not parallel to the surface (they are not horizontal on the Moon) http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment#mediaviewer/File:ALSEP_AS14-67-9386.jpg http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment#mediaviewer/File:Apollo_11_Lunar_Laser_Ranging_Experiment.jpg I nearly said 'yes" but really it is "No" the Earth spins 29 times as fast. The Moon is still orbiting the Earth slowly (about 29 days) All my figures are rough estimates, precise details are available. If we want to hit a reflector on the Moon we have to take into account both the light time delay and the 1km/sec orbital velocity of the moon. It takes ~1.25 sec for light to travel from Moon to Earth, so the light we see is 1.25 sec old, which means the Moon has moved ~1.25 km in the time it took for its image to reach us. It will also take ~1.25 sec for laser we fired to hit the Moon, during which time the Moon has moved an additional ~1.25 km. Assuming we are aiming at a reflector that is fairly small, we aim our laser ~2.5 km ahead of where we see the reflector. Now, it will take ~2.5 sec for the laser to make the round trip, during which time the image of the Moon we see in the sky moves ~2.5 km. Since we "lead" the reflector by ~2.5 km when we fired the laser, the image carrying the refection will have moved exactly to the spot where we aimed the laser. IOW, the reflection we see comes back from the same direction as we aimed the laser. I think the speed that the laser and the receiver is moving transversely to the reflector is much more important than the motion of the Moon. but I stand to be corrected. Is the gun and receiver separated by a kilometer or so? Wikipedia:http://en.wikipedia.org/wiki/Earth%27s_rotation#Angular_speed.... equatorial speed of 465.1 m/s Link to comment Share on other sites More sharing options...
michel123456 Posted November 22, 2014 Author Share Posted November 22, 2014 If we want to hit a reflector on the Moon we have to take into account both the light time delay and the 1km/sec orbital velocity of the moon. It takes ~1.25 sec for light to travel from Moon to Earth, so the light we see is 1.25 sec old, which means the Moon has moved ~1.25 km in the time it took for its image to reach us. It will also take ~1.25 sec for laser we fired to hit the Moon, during which time the Moon has moved an additional ~1.25 km. Assuming we are aiming at a reflector that is fairly small, we aim our laser ~2.5 km ahead of where we see the reflector. Now, it will take ~2.5 sec for the laser to make the round trip, during which time the image of the Moon we see in the sky moves ~2.5 km. Since we "lead" the reflector by ~2.5 km when we fired the laser, the image carrying the refection will have moved exactly to the spot where we aimed the laser. IOW, the reflection we see comes back from the same direction as we aimed the laser. Provided that the screen is perpendicular to the beam, i suppose. Does the following diagram depicts roughly the situation? Link to comment Share on other sites More sharing options...
davidivad Posted November 22, 2014 Share Posted November 22, 2014 (edited) even our own reflections are the past. you cannot see him nor he you. heck, you cant even see your current reflection as this is a different frame of reference. Edited November 22, 2014 by davidivad Link to comment Share on other sites More sharing options...
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