michel123456 Posted December 6, 2014 Posted December 6, 2014 An electron doesn't grow like a circle as it gets farther in the past. If we went back in time people would not look like giant disks. The cone shows what part of the past can be observed. It takes time for light to travel from a to b.For one second in the past the sphere would have a radius of 186000 miles. The cone is a BOUNDARY. To see outside of the cone would require a signal traveling faster then light. As you go farther back the boundary grows. The particles do not grow. Traveling backwards in time would mean your worm makes a u turn. You are still moving foward in your time but your time is moving in the opposite direction of everyone else's time. Imagine a 2d graph where y is the time axis and x is the distance axis. Draw a upside down V. This would be a point that is traveling forward in time and then reverses it's direction in time. If you are observing this and you don't reverse your direction in time you could mistake this with two particles coming together and then disappearing when they meet. This is how Feynman describes matter and antimatter annihilating each other. An electron emits two photons. Instead of it recoiling the opposite direction in space it recoils the opposite direction in time. We reverse the arrow of time on the backwards traveling electron. When we do this we must also reverse its charge, spin, and matter antimatter classification. I said the twin paradox shows the past is not gone. When twins travel at different speeds there clocks get out of sync. What appears simultaneously to one would happen at different times for the other. 5 o'clock for one would be 4 o'clock for the other. If only the present exists then at 5 o'clock only one twin could exist. The other is at 4 o'clock and 4 o'clock no longer exists. Since you seem to understand the cone very well, a simple question in the hope to find (maybe) someone who understands me: You wrote The cone is a BOUNDARY. To see outside of the cone would require a signal traveling faster then light. What about the inside part of the cone? can we directly observe the inside part of the cone? To see inside would require a signal travelling slower than light.
michel123456 Posted December 6, 2014 Author Posted December 6, 2014 when light travels through air or some other medium it travels slower. Refractive index equals c/v c is the speed in a vacuum v is the speed through a medium. Bats see with sonar which travels at the speed of sound. Fully correct, but that was not the expected answer. I ment, for example, can you directly see your own past (which is inside your past cone) ?
david345 Posted December 6, 2014 Posted December 6, 2014 Fully correct, but that was not the expected answer. I ment, for example, can you directly see your own past (which is inside your past cone) ? Are you asking about time travel? You could see your past by looking in the mirror. It takes time for the light to reach you. You could use a slower signal to see farther back.
michel123456 Posted December 6, 2014 Author Posted December 6, 2014 Are you asking about time travel? You could see your past by looking in the mirror. It takes time for the light to reach you. You could use a slower signal to see farther back. Not about time travel. About the content of the past light cone. Another example: from where we are now, can we observe the Earth 10 days ago?
david345 Posted December 7, 2014 Posted December 7, 2014 (edited) Some are under the impression that a particle moves along the time line. This would require a second time. It takes time for a particle to move along the distance line and it would take a second time for a particle to travel along the time line. How fast does a particle travel along the time line? A second per hour? Does one person's time move faster then another person's time? This happens in relativity. It is a result of the Lorentz contraction. It is not a result of one person flowing along the time line faster then another. What if there is a second time? Do things move along this time line? This would require a third time. Not about time travel. About the content of the past light cone. Another example: from where we are now, can we observe the Earth 10 days ago? If you have a signal that takes 10 days to get from earth to you. Otherwise you would have to time travel. Edited December 7, 2014 by david345
michel123456 Posted December 7, 2014 Author Posted December 7, 2014 Some are under the impression that a particle moves along the time line. This would require a second time. It takes time for a particle to move along the distance line and it would take a second time for a particle to travel along the time line. (...) That is a confusing argument. If you have a set of 4 coordinates xyzt, does it take time to change from 0,0,0,0 to 0,0,0,1 ? One would say Yes, it takes 1 unit of time. Now, does it take time to change from 0,0,0,0 to 1,0,0,0? Mathematically, one would say no, because the T coordinate has not changed, but physically following Relativity we know it is not allowed. Anyway I don't think you need a fifth dimension (a second time) to study or make these changes.
david345 Posted December 7, 2014 Posted December 7, 2014 That is a confusing argument. If you have a set of 4 coordinates xyzt, does it take time to change from 0,0,0,0 to 0,0,0,1 ? One would say Yes, it takes 1 unit of time. Now, does it take time to change from 0,0,0,0 to 1,0,0,0? Mathematically, one would say no, because the T coordinate has not changed, but physically following Relativity we know it is not allowed. Anyway I don't think you need a fifth dimension (a second time) to study or make these changes. Imagine a point in (x,t). Imagine that point moving either along the t axis or along the world line. Does it travel from t1 to t2 instantly? Does it travel from w1 (world line point 1) to w2 instantly? If it traveled from t1 to t2 instantly then it would be at all points between at the same time. The same for w1 to w2. If it is not at all points between at the same time then it would take A PERIOD OF TIME to travel between t1 and t2, w1 and w2. You speak of travel between (0,0,0,0) and (0,0,0,1), and (0,0,0,0) and (1,0,0,0). Is this travel instantly or does it take time or is it neither instantly or takes time?
michel123456 Posted December 7, 2014 Author Posted December 7, 2014 Imagine a point in (x,t). Imagine that point moving either along the t axis or along the world line. Does it travel from t1 to t2 instantly? Does it travel from w1 (world line point 1) to w2 instantly? If it traveled from t1 to t2 instantly then it would be at all points between at the same time. The same for w1 to w2. If it is not at all points between at the same time then it would take A PERIOD OF TIME to travel between t1 and t2, w1 and w2. You speak of travel between (0,0,0,0) and (0,0,0,1), and (0,0,0,0) and (1,0,0,0). Is this travel instantly or does it take time or is it neither instantly or takes time? No, it needs one unit of time. i don't understand why you are confused. OTOH if it traveled "instantly" from T1 to T2, that would mean the object would be 'at the same time" at T1 and T2. IOW it would be a line upon the T axis, the standard representation of an object in time. And i disagree with that last.
david345 Posted December 8, 2014 Posted December 8, 2014 No, it needs one unit of time. i don't understand why you are confused. OTOH if it traveled "instantly" from T1 to T2, that would mean the object would be 'at the same time" at T1 and T2. IOW it would be a line upon the T axis, the standard representation of an object in time. And i disagree with that last. It would take a unit of a second time to travel between t1 and t2. The difference between t1 and t2 is the distance the point must travel. We will call that distance 1 sec. How long does it take for a point to travel a distance of 1 sec. You can not use the distance a point must travel as the time it takes to travel that distance. That would be like saying I am moving at a speed of a mile per mile. It could take a long time for the point to travel 1 sec. It could travel this distance in a short time. This is why you would need a second time to tell how long it takes for the point to travel a distance of 1 sec on the time line. Even if it traveled 1 sec per 1 sec that would be one second of the new time to travel one second of the old time.
Robittybob1 Posted December 8, 2014 Posted December 8, 2014 It would take a unit of a second time to travel between t1 and t2. The difference between t1 and t2 is the distance the point must travel. We will call that distance 1 sec. How long does it take for a point to travel a distance of 1 sec. You can not use the distance a point must travel as the time it takes to travel that distance. That would be like saying I am moving at a speed of a mile per mile. It could take a long time for the point to travel 1 sec. It could travel this distance in a short time. This is why you would need a second time to tell how long it takes for the point to travel a distance of 1 sec on the time line. Even if it traveled 1 sec per 1 sec that would be one second of the new time to travel one second of the old time. That sounds confused to me.
david345 Posted December 8, 2014 Posted December 8, 2014 That sounds confused to me.Is that your best refute?
Robittybob1 Posted December 8, 2014 Posted December 8, 2014 Is that your best refute? Yes it was too confusing to see how to straighten it out. I thought I'd give you time to change it.
david345 Posted December 8, 2014 Posted December 8, 2014 (edited) Yes it was too confusing to see how to straighten it out. I thought I'd give you time to change it. A point can move fast between a and b or it can move slowly between a and b. How long does it take for the point to travel from t1 to t2. We will call this interval 1 sec. Your buddy Michel claimed it takes 1 sec. to travel between t1 and t2. What if the point travels at twice the speed? Does it still take the same time to travel from t1 to t2 even though the point is traveling twice as fast? The idea of flowing time is incoherent. Edited December 8, 2014 by david345
imatfaal Posted December 8, 2014 Posted December 8, 2014 Since you seem to understand the cone very well, a simple question in the hope to find (maybe) someone who understands me: You wrote What about the inside part of the cone? can we directly observe the inside part of the cone? To see inside would require a signal travelling slower than light. Inside the cone - that is the volume we can interact with; the cone surface itself is light speed interactions and the interior is sub-luminal. The light cone surface is the outer/furthest limit of that with which we can interact in the future - and the past cone is that which could have influenced us in the past
imatfaal Posted December 8, 2014 Posted December 8, 2014 i dont think light cones are real... Tangible no, concrete definitely not - but a representation of our volume of influence they are very important and useful. Also remember that the cone shape is confusing as that is missing a dimension
michel123456 Posted December 8, 2014 Author Posted December 8, 2014 (edited) It would take a unit of a second time to travel between t1 and t2. The difference between t1 and t2 is the distance the point must travel. (...) At that point you lost me. The "distance" is measured in time. Its value is one unit. In time. Inside the cone - that is the volume we can interact with; the cone surface itself is light speed interactions and the interior is sub-luminal. The light cone surface is the outer/furthest limit of that with which we can interact in the future - and the past cone is that which could have influenced us in the past I am not allowed to reintroduce a thread that has fallen (or has been propulsed) into the Forum Trash can. If you are not afraid to deal with dirty things you can go there and have a look. http://www.scienceforums.net/topic/43241-space-time-diagram Note that, as usual, I haven't change my mind since. And it was in 2009! Edited December 8, 2014 by michel123456
Strange Posted December 8, 2014 Posted December 8, 2014 Note that, as usual, I haven't change my mind since. And it was in 2009! You sound almost proud of having failed (refused?) to learn anything in 15 years. Not impressive. 2
MigL Posted December 9, 2014 Posted December 9, 2014 Michel123456, why would a co-ordinate change ? And why would it take time to change assuming it could ? A co-ordinate is a FIXED reference point on a 4D grid. Events, or things, can occupy different co-ordinates as they move or age. Using (x,y,z,t), it takes I unit of time for an event's present to go from (0,0,0,0) to (0,0,0,1). Note that it has not moved. The alternate motion from (0,0,0,0) to (1,0,0,0), is NOT ALLOWED as it implies instantaneous motion and disregards c. so your question is meaningless. You will never be able to see events in your own past. That is not what a light cone represents. You cannot separate fast enough from an event so as to outrace the light coming from that event ( on sub-cosmological scales anyway ).
Ophiolite Posted December 9, 2014 Posted December 9, 2014 You sound almost proud of having failed (refused?) to learn anything in 15 years. Not impressive. He said 2009. That's five years, not fifteen. Are you in a different light cone? 2
david345 Posted December 9, 2014 Posted December 9, 2014 (edited) I have come up with a proof to settle this once and for all. You say time flows at a speed of 1 sec per sec. I will now prove that if time moves one sec per sec then space must move 1 mile per mile. The problem is that you are treating time as both a temporal distance and a spatial distance. Speed=d/t you say d\t=t\t this would mean t=t AND t=d if t=d then d=t if d=t then d\t=d\d You say time moves one second per second. I could equivalently say space moves one mile per mile. It does not take one unit of time to go from (0,0,0,0) to (0,0,0,1). The difference between (0,0,0,0) and (0,0,0,1) is one unit of time. DISPUTE SETTLED. Edited December 9, 2014 by david345
Strange Posted December 9, 2014 Posted December 9, 2014 He said 2009. That's five years, not fifteen. Are you in a different light cone? No. Just incompetent.
imatfaal Posted December 9, 2014 Posted December 9, 2014 The surface of the cone is information transfer at lightspeed and the interior is information transfer at sub-luminal speeds; Sisyphus said it 5 years ago and I repeated it above - without prompting I am unsure from this thread or the old one what you do not understand; you can interact with everything within your future lightcone, and can have been influenced with (and vice versa) everything in your past light cone - the limit of this interaction is the boundary of the cone which is the surface reached by travelling at the maximum speed of interaction (ie light speed)
michel123456 Posted December 9, 2014 Author Posted December 9, 2014 Michel123456, why would a co-ordinate change ? And why would it take time to change assuming it could ? A co-ordinate is a FIXED reference point on a 4D grid. Events, or things, can occupy different co-ordinates as they move or age. Using (x,y,z,t), it takes I unit of time for an event's present to go from (0,0,0,0) to (0,0,0,1). Note that it has not moved. The alternate motion from (0,0,0,0) to (1,0,0,0), is NOT ALLOWED as it implies instantaneous motion and disregards c. so your question is meaningless. You will never be able to see events in your own past. That is not what a light cone represents. You cannot separate fast enough from an event so as to outrace the light coming from that event ( on sub-cosmological scales anyway ). At least we agree on something: You will never be able to see events in your own past. Yes, exactly. That is what a lightcone represents. Our past is inside our light cone and it is not directly observable. What I say, now than 5 years, is that most if not all signals we get from the universe are traveling at c. As a consequence, all informations we gather are upon the surface of the lightcone. Not outside, not inside. I really don't understand what is wrong with that. There is of course other kind of information, like dinosaurs bone. But that does not give information about the universe, that gives information about us.
elfmotat Posted December 9, 2014 Posted December 9, 2014 What I say, now than 5 years, is that most if not all signals we get from the universe are traveling at c. That's just false. How about sound waves? Humans use those pretty often.
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