asprung Posted February 5, 2009 Share Posted February 5, 2009 How is it that an earth twin and space twin can both continuously share the same "now" while there clocks run at different rates? The universe only exists "now" its past is but history formed of a collection of successive past "now’s" and its future is yet to arrive. It follows that events can only occur "now" and that the lag between events occurring during former and later "now’s” cannot be measured by clocks. Thus a twin traveling at a speed approaching the speed of light, and his earth twin should share the same "now" while there clocks would run at different rates. Each event occurring could be viewed simultaneously by each of the twins (adjusting for the differences in time it would take a signal from the event to reach the respective twin). When the space twin returns to earth, since he shares earths "now" he could step on to earth and merely adjust his calendar and clock to earths. If this were not so he would find himself in earth's non-existent past with earth in his future. Since the twins continuously share the same "now’" they should be the same biological age, though their clocks would indicate vastly different ages. I do not know how the speed of the progression of "now" would be measured. It would have to be fast enough so that light could not pass into the nonexistent future. Maybe the speed of “now” is the brake on the speed of light. In any event, the rate of the passage of "now" would seem to be the correct measure of the aging of the universe. Link to comment Share on other sites More sharing options...
NowThatWeKnow Posted February 6, 2009 Share Posted February 6, 2009 Since the twins continuously share the same "now’" they should be the same biological age, though their clocks would indicate vastly different ages. That isn't the way the story goes. The atomic clock, windup clock and biological clock all agree. http://www.phys.unsw.edu.au/einsteinlight/jw/module4_twin_paradox.htm You should read this site (insert your favorite word). Link to comment Share on other sites More sharing options...
moth Posted February 6, 2009 Share Posted February 6, 2009 once the twins start moving relative to each other they start having trouble agreeing when "now" is. http://en.wikipedia.org/wiki/Relativity_of_simultaneity 1 Link to comment Share on other sites More sharing options...
swansont Posted February 6, 2009 Share Posted February 6, 2009 This is a semantic argument, not a physics one. It's always "now" for any observer. Physics demands more rigor than this. Link to comment Share on other sites More sharing options...
asprung Posted February 6, 2009 Author Share Posted February 6, 2009 "now" is when the event occurs, and is the same for both twins. They only dissagree as to its time. 1 Link to comment Share on other sites More sharing options...
D H Posted February 6, 2009 Share Posted February 6, 2009 "now" is when the event occurs By saying that you are implicitly assuming that true simultaneity is a valid concept in physics. True simultaneity does not exist. Some reading material for you: http://en.wikipedia.org/wiki/Relativity_of_simultaneity http://physics.suite101.com/article.cfm/simultaneity_and_relativity Link to comment Share on other sites More sharing options...
NowThatWeKnow Posted February 6, 2009 Share Posted February 6, 2009 "now" is when the event occurs, and is the same for both twins. They only dissagree as to its time. Twin A's 2008 is twin B's 2009. So an event could happen in two different years yet happen at the same time or "now" as you say. You could demonstrate this after the trip was over. Each twin may disagree on the year of a recent event, but agree it happened 1 hour ago. However, from two different frames they will not agree. I can relate to your thought process but I am usually wrong. Link to comment Share on other sites More sharing options...
moth Posted February 6, 2009 Share Posted February 6, 2009 "now" is when the event occurs, and is the same for both twins. They only dissagree as to its time. each twin has a different perception of how "fast" time is passing. one twins "now" could be the other twins 5 minutes. how long does "now" last? Link to comment Share on other sites More sharing options...
NowThatWeKnow Posted February 6, 2009 Share Posted February 6, 2009 each twin has a different perception of how "fast" time is passing. one twins "now" could be the other twins 5 minutes. how long does "now" last? It could be instantaneous like a digital change. Using the theory of relativity you could calculate an exact time for every location in space and that could be used for a now time. Just like clocks for different time zones we could have clocks for different locations in the universe that would run at different speeds. They would be displaying a now time for different frames. Link to comment Share on other sites More sharing options...
asprung Posted February 7, 2009 Author Share Posted February 7, 2009 If the universe only exists "now" the twins would have to share the same "nows". If not they would pass into the past and future with respect to each other and the space twin could not return to the earths present. Link to comment Share on other sites More sharing options...
moth Posted February 7, 2009 Share Posted February 7, 2009 Just like clocks for different time zones we could have clocks for different locations in the universe that would run at different speeds. They would be displaying a now time for different frames. when you move away from where and when you made the map it will need corrections with the Lorentz factor Merged post follows: Consecutive posts mergedIf the universe only exists "now" the twins would have to share the same "nows". If not they would pass into the past and future with respect to each other and the space twin could not return to the earths present. they can get back to a place where they both agree when "now" is but they will disagree on how much time has elapsed since they first separated. Link to comment Share on other sites More sharing options...
john5746 Posted February 7, 2009 Share Posted February 7, 2009 If the universe only exists "now" the twins would have to share the same "nows". If not they would pass into the past and future with respect to each other and the space twin could not return to the earths present. Whatever, so there is not past, present or future to worry about. The space twin returns to earth and both twins are on the earth "now". But the space twin is younger than the earth twin. In fact, the earth twin might be long dead, but they are both on earth "now". Link to comment Share on other sites More sharing options...
NowThatWeKnow Posted February 7, 2009 Share Posted February 7, 2009 If the universe only exists "now" the twins would have to share the same "nows". If not they would pass into the past and future with respect to each other and the space twin could not return to the earths present. That is the point being made by the twins paradox, the space twin does return to Earth's future according to the clock on the space ship. A 12 year 1G rocket ride for you would mean 100,000+ years will pass on Earth. Merged post follows: Consecutive posts mergedwhen you move away from where and when you made the map it will need corrections with the Lorentz factor Travelers would require a computer controlled time keeping system. There is no reason why you could not calculate Earth time while traveling. Just thinking out loud and not suggesting anything that would be practical. Link to comment Share on other sites More sharing options...
swansont Posted February 7, 2009 Share Posted February 7, 2009 If the universe only exists "now" the twins would have to share the same "nows". If not they would pass into the past and future with respect to each other and the space twin could not return to the earths present. They do share the same "now." They just disagree on what time "now" is. I don't see what the problem is. Well, I do, actually — "now" isn't a well-defined term in physics, which is why these discussions occasionally sound like an Abbott & Costello bit. Link to comment Share on other sites More sharing options...
NowThatWeKnow Posted February 7, 2009 Share Posted February 7, 2009 ...which is why these discussions occasionally sound like an Abbott & Costello bit. I resemble that remark. Link to comment Share on other sites More sharing options...
asprung Posted February 7, 2009 Author Share Posted February 7, 2009 It seems that most agree that the twins share the same "nows" though their clocks may run at diffrent speeds. I believe that the true ageing of the universe is determined by the rate of advancment of "nows" and that this should also determin the twins ageing and not the speed of their clocks. Link to comment Share on other sites More sharing options...
D H Posted February 7, 2009 Share Posted February 7, 2009 It seems that most agree that the twins share the same "nows" though their clocks may run at diffrent speeds. True simultaneity, and hence a universal "now", does not exist. Please read the links in post #6. Link to comment Share on other sites More sharing options...
swansont Posted February 7, 2009 Share Posted February 7, 2009 It seems that most agree that the twins share the same "nows" though their clocks may run at diffrent speeds. I believe that the true ageing of the universe is determined by the rate of advancment of "nows" and that this should also determin the twins ageing and not the speed of their clocks. What is the difference between the two? From my interpretation of the undefined phrase "advancement of nows" I'd say that's exactly what clocks measure. Thus the speed of time, as measured by the clocks, is precisely what determines their aging. Link to comment Share on other sites More sharing options...
NowThatWeKnow Posted February 7, 2009 Share Posted February 7, 2009 The definition of "now" http://www.einstein-online.info/en/spotlights/Now/index.html "two events are simultaneous if and only if they can be seen on the same photograph, taken with a double camera placed exactly in the middle between their locations." Link to comment Share on other sites More sharing options...
asprung Posted February 8, 2009 Author Share Posted February 8, 2009 If the twins start at the same "now" and end at the same "now' with their clocks, which measure time, showing diffrent values, time as we measure it cannot accuratly show the rate of progression of "now". Link to comment Share on other sites More sharing options...
NowThatWeKnow Posted February 8, 2009 Share Posted February 8, 2009 If the twins start at the same "now" and end at the same "now' with their clocks, which measure time, showing diffrent values, time as we measure it cannot accuratly show the rate of progression of "now". Your head ages faster then your feet and they share the same "now". "...sound like an Abbott & Costello bit." Yep Link to comment Share on other sites More sharing options...
swansont Posted February 8, 2009 Share Posted February 8, 2009 If the twins start at the same "now" and end at the same "now' with their clocks, which measure time, showing diffrent values, time as we measure it cannot accuratly show the rate of progression of "now". The conclusion of relativity is that time is not an absolute. "Now" is not an absolute — it's the time displayed on your clock. You keep treating them as different things, and they aren't. Merged post follows: Consecutive posts mergedYour head ages faster then your feet and they share the same "now". "...sound like an Abbott & Costello bit." Yep What time is it? Now. Yes, now. I want to know what time it is now. Yes. The time. Now. Yes, now. Yes. Link to comment Share on other sites More sharing options...
asprung Posted February 22, 2009 Author Share Posted February 22, 2009 Do the space twins share the same “now” and progression of “nows”? If not how would they simultaneously view an event and not fall into the past and future with respect to each other? Link to comment Share on other sites More sharing options...
swansont Posted February 22, 2009 Share Posted February 22, 2009 Do the space twins share the same “now” and progression of “nows”? If not how would they simultaneously view an event and not fall into the past and future with respect to each other? You really have to get past using these ill-defined terms. In science we try and quantify things. Time is not an absolute. Twin A measuring the time to be Ta and twin B measuring it to be Tb does not put one of them in the other's past or future. Link to comment Share on other sites More sharing options...
ydoaPs Posted February 22, 2009 Share Posted February 22, 2009 The conclusion of relativity is that time is not an absolute. "Now" is not an absolute — it's the time displayed on your clock. You keep treating them as different things, and they aren't. Merged post follows: Consecutive posts merged What time is it? Now. Yes, now. I want to know what time it is now. Yes. The time. Now. Yes, now. Yes. Who's on first? Link to comment Share on other sites More sharing options...
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