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write4u
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What part of the measurement of time is called 'world line' or 'world braid'? And how is it measured?
QuantumPion said:... If you took two cesium atoms, one on a flying jet and the other on the ground, by the time the atom on the ground produced 9,192,631,770 periods of radiation the one on the jet will have produced say 9,192,631,769 periods of radiation. This is because the atom on the jet experienced less time compared to the atom on the ground.
Salman2 said:...Do we not say the second horse was slower than the first because it took a longer time to reach the finish line ? I do not see why Einstein would grant 'time' as a concept the same physical status as 'horse' and say that both move slow or fast ? ...
LastOneStanding said:There is indeed a difference between time as something that locates an event in space-time ("coordinate time") and time as something measured by clocks ("proper time").
LastOneStanding said:Time dilation isn't something that just happened to the atomic clocks; it happened to every dynamical process.
A "world line" is the curve in spacetime that describes the motion of a point-like object. The term "world braid" is non-standard, I think. I googled it, and didn't get any physics-related hits on the first two pages. Wikipedia uses the following terminology:write4u said:What part of the measurement of time is called 'world line' or 'world braid'? And how is it measured?
SR defines two kinds of time, "coordinate time" and "proper time". A coordinate system is a function x that associates a 4-tuple ##(x^0(p),x^1(p),x^2(p),x^3(p))## with each p in M. The number ##x^0(p)## is the coordinate time (or time coordinate) of p.azoulay said:QuantumPion, what's your definition of time ?
They "measure" the proper time of the curves in spacetime that describe their motion, in the sense that if a clock displays t at one event and t' at another, then the proper time of the part of the clock's world line from the former event to the latter event is t'-t.azoulay said:LastOneStanding, you say that clocks are measuring "something", what is that "something"?
azoulay said:So I'm not saying Einstein was wrong, what I'm saying is that Einstein probably could of written all his theory talking only about movements and to never having to use the word "time".
azoulay said:Could you please give me examples of some dynamical process where time dilation happens ?
If anyone wants to reply to the above, PLEASE start your reply with a clear and unambiguous definition of "time".
IOW, 'multiple measurements' can only be made after the new coordinates have been established (after the event). Before then the destination coordinates were not yet known and duration of time was only a latent 'probability' for that event.World lines aren't measured. What you measure is the position of the object. If you make multiple measurements, you can draw the object's world line.
That doesn't have anything to do with world lines.write4u said:Still looking for the science article with the term world braids, but perhaps this may clarify,
http://en.wikipedia.org/wiki/Braid_group
This is at best philosophy. It certainly isn't physics.write4u said:IMHO, time is a potential measurement of duration of motion and becomes explicate and measurable only during that motion or change.
I see Time as a fundamental potential, a "latency" which becomes an expressed non-physical property of an event or movement, which by needs 'requires' and 'uses' time.
azoulay said:So the definition of time for me has always been that it's an abstract representation of some movement and nothing else.
You are contradicting yourself yet again. First you say that time represents some movement, then you say that clocks measure some movement. Therefore your obvious conclusion should be that clocks measure time. For you to conclude what clocks measure is "not time" is a self-contradiction.azoulay said:So clocks really keep tracks of MECHANICAL MOVEMENTS, not time:
Exactly.azoulay said:So yes, "time" is relative (Einstein was right) but only if the definition of time has to do with MECHANICAL MOVEMENTS. Bottom line, to put it simply: it is MECHANICAL MOVEMENTS that is relative.
I like Einstein's definition (simplified): "time is what a clock measures (proper time) together with a simultaneity convention (coordinate time)". That is the essence of Einstein's section 1, and is a clear and unambiguous experimental definition of time.azoulay said:If anyone wants to reply to the above, PLEASE start your reply with a clear and unambiguous definition of "time".
Time dilation occurs with EM processes (e.g. atomic clocks), weak force processes (e.g. muon decay), strong force processes (e.g. pion decay), and gravity (e.g. gravitational potential). All dynamical processes are based on one or more of those fundamental forces so all dynamical processes exhibit time dilation.azoulay said:Could you please give me examples of some dynamical process where time dilation happens ?
It will take a real genius to fulfill your request.azoulay said:...
Conclusion 2: I think, it would be possible in science to never use the word "time" and only use the word "movement".
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Einstein probably could of written all his theory talking only about movements and to never having to use the word "time".
If some genius one day wants to rewrite Einstein theory and set aside the word "time" and use only the word "movement" it would be, I think, a lot more comprehensible and intuitive for everyone.
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If anyone wants to reply to the above, PLEASE start your reply with a clear and unambiguous definition of "time".
ghwellsjr said:Events don't have speeds. And an observer's view of events does not change depending on anything.
ghwellsjr said:Clinging to the idea of an absolute reference frame does not change any observations. It also does not change any predictions (as long as you have a correctly working theory based on an absolute reference frame). That sounds like a modern incarnation of Lorentz's Ether Theory. You should be clearer when making statements like this, as is, they sound confusing.
ghwellsjr said:If you want to take Einstein's special theory of relativity, then you must reconcile with time dilation. It's not an option. And it is more than simply our ability to observe, given our medium. Are you talking about Ether?
ghwellsjr said:You sound like you're on shaky ground.
An event is a point in the spacetime manifold. It has no spatial nor temporal extent, and as a result it does not have a speed. It most definitely does not change as a function of time.Bhumble said:I don't understand how an event does not have a speed (or more specifically a time dependence). I'm not sure how else would you describe an event other than some setting changing as a function of time?
Bhumble said:I agree completely for matter that has an electromagnetic interaction but I suppose I still have reservations considering the majority of the matter in the universe seemingly does not interact with light and COULD very well have different limitations.
Is there any suggestion in quantum theory that an event, as a point in spacetime manifold, has the spatial and temporal extent of Planck-space and Planck-time ? Thus, given that both Planck-space and Planck-time are outside possibility of human measurement, could this help explain why all events in spacetime manifold do not change as a function of time ? The suggestion being that events as points in spacetime would be outside the limit of human ability to measure change because they occur within Planck-space and Planck-time, which by definition also are outside the spacetime manifold ?DaleSpam said:An event is a point in the spacetime manifold. It has no spatial nor temporal extent, and as a result it does not have a speed. It most definitely does not change as a function of time.
Salman2 said:Is there any suggestion in quantum theory that an event, as a point in spacetime manifold, has the spatial and temporal extent of Planck-space and Planck-time ? Thus, given that both Planck-space and Planck-time are outside possibility of human measurement, could this help explain why all events in spacetime manifold do not change as a function of time ?
OK. Suppose we have two synchronized clocks and they start motion at the same place in spacetime, and we find that they return to that place simultaneously as an event, and the dτ/dt = 0.99 for one clock, and dτ/dt = 0.90 for the second. I do not see why it is semantics to say that one clock moved faster or slower relative to the other because time as measured by dτ/dt was shorter or longer ? Sorry, but I just do not understand how the math dτ/dt demands that time cannot be understand as long (or many) or short (or few) when the motion of what the time measures is labeled as fast or slow.DaleSpam said:I think you are getting hung up on the english. You seem to be stuck on "long" and "short" rather than "fast" and "slow". The important part is that dτ/dt<1 for a moving clock, do you understand that?
OK, then how are these 'points in space-time' defined ? If they are defined using Planck scale does this not open a door for a way to unite relativity theory and quantum theory ?LastOneStanding said:Events don't have spatial or temporal extent because they are defined to be points in space-time. Quantum theory has nothing to do with it.
In SR, we describe events with their coordinates according to a specified Inertial Reference Frame (IRF). There are four coordinates--three spatial and one time. We can then transform the coordinates of all the events according to a new IRF moving with respect to the original IRF and we will get a new set of coordinate values but we should never conflate the coordinates of one IRF with the coordinates of another IRF so we don't ever want to let the fact that their is motion between the IRF's lead us into the false notion that their is any motion to events. Each event is described as occurring at an instant in time at a specific location in space according to the coordinates of a specific IRF.Bhumble said:I don't understand how an event does not have a speed (or more specifically a time dependence). I'm not sure how else would you describe an event other than some setting changing as a function of time?ghwellsjr said:Events don't have speeds. And an observer's view of events does not change depending on anything.
If you are talking about a scenario where you don't specify when the ball dropped into the hole but rather when the ball was launched at some speed and angle from a cannon for example and we have to figure out its trajectory, then the IRF matters because distances as well as times are relative to the IRF and we can get different answers to the question of when the ball dropped into the hole as well as different answers to the question of how fast was the ball moving. Is that what you are concerned about?Bhumble said:Assuming that you agree that an event does have a time dependence. Then doesn't it follow that the perception of time passing depends on the reference frame of the observer. Say you describe an event as a ball dropping into a hole. Is the time that this event occurred invariant to the speed that the ball drops and the reference frame of the observer?
Salman2 said:OK, then how are these 'points in space-time' defined ? If they are defined using Planck scale does this not open a door for a way to unite relativity theory and quantum theory ?
The spacetime manifold is part of relativity, which is a classical theory, not a quantum theory. I think your question will be answered once we get a working quantum theory of gravitySalman2 said:Is there any suggestion in quantum theory that an event, as a point in spacetime manifold, has the spatial and temporal extent of Planck-space and Planck-time ?
I appreciate your comments. Here is an unpublished report from a physicist associated with CERN where a suggestion is made how the Planck scale could enter into a spacetime manifold, so it does appear that my question is not completely off base:LastOneStanding said:They are defined by basic topology. I think you need to learn what a manifold is. The Planck scale does not enter into it anywhere.
Salman2 said:I appreciate your comments. Here is an unpublished report from a physicist associated with CERN where a suggestion is made how the Planck scale could enter into a spacetime manifold, so it does appear that my question is not completely off base:
http://cds.cern.ch/record/368952/files/9810174.pdf
I didn't say that you couldn't understand it in terms of English words, just that whatever words you choose use to express the ideas need to correspond to that mathematical expression. Einstein used the word "slow" to refer to dτ/dt<1. You prefer "long" or "short". As long as you are using those words to refer to dτ/dt<1 then you are correct, if you are not then you are wrong.Salman2 said:Sorry, but I just do not understand how the math dτ/dt demands that time cannot be understand as long (or many) or short (or few) when the motion of what the time measures is labeled as fast or slow.
LastOneStanding said:They are defined by basic topology. I think you need to learn what a manifold is. The Planck scale does not enter into it anywhere.
1. Depends on which two points in space we're talking about, and your choice of what to call "space".write4u said:How big is the distance between spatial points that keep things apart? How do we measure the time interval between spatial points? What size is the graininess of spacetime?
Nugatory said:The muon decay measurements have always been one of my favorites. High energy cosmic rays hit the atmosphere about 100 km up, giving rise to very short-lived particles called muons. These muons decay so quickly that they shouldn't be able to hit the surface of the Earth - even though they're moving at nearly the speed of light, it still takes a few hundred microseconds for them to travel 100 km, and they don't live that long.
But they do reach the surface of the earth. That's time dilation at work.
azoulay said:If science is willing to consider "time" as being a representation of a mechanical movement, then science should try to explain why a muon reaches Earth in terms of a mechanical movement (not time dilation that's disconnected from physical/mechanical reality).
If we assume that time is always related to some kind of mechanical movement
Note that "this effect" refers to the fact that the numbers displayed by clocks agree with the proper times of their world lines. If there's something worth protesting against here, it's that this is called an "effect". It's just a description of what clocks do. It's not explained by the theory, it's one of the assumptions that defines the theory.azoulay said:If we assume that time is always related to some kind of mechanical movement, then it is not true to say that "This effect arises neither from technical aspects of the clocks nor from the fact that signals need time to propagate, but from the nature of spacetime itself" because then you need another definition of "time", one which has nothing to do with mechanical movements.
And that's exactly the magical notion of "time" I'm fighting against in this thread.
Fredrik said:Note that "this effect" refers to the fact that the numbers displayed by clocks agree with the proper times of their world lines. If there's something worth protesting against here, it's that this is called an "effect". It's just a description of what clocks do. It's not explained by the theory, it's one of the assumptions that defines the theory.
LastOneStanding said:There is no "mechanical" explanation because there's nothing mechanical in the scenario! The muon is an elementary particle, there are no "internal workings", no ticking clock inside of it.
No one is assuming that but you. The definition of time being used in special relativity has been given to you many times now, I see no reason to repeat it.
Everything that has been explained to you is based on rigorous mathematics and has been tested by a battery of experiments. That is science, not magic. You just don't like it. Well, tough: nature doesn't care what you like.
That is your definition, not science's. However, it isn't too bad. The only real problem with it, IMO, is that it is too restrictive on what is considered a clock. I would allow clocks with no moving parts to measure time also.azoulay said:If science is willing to consider "time" as being a representation of a mechanical movement
If you have a large number of muons at rest next to a good mechanical clock then you will find that with each tick of the clock the same fraction of muons decay. By YOUR definition of time, that means that the same fraction of muons decay over each interval of time. This is a law which governs the behavior of muons.azoulay said:, then science should try to explain why a muon reaches Earth in terms of a mechanical movement (not time dilation that's disconnected from physical/mechanical reality).
Why not? What makes this magical in any way? We have a scientific theory, in that theory we propose that spacetime has certain symmetries. We investigate the logical conclusion of those symmetries and find that if spacetime does have those symmetries then time will dilate. We hypothesize that if our theory is correct then fast moving muons will decay more slowly than stationary muons. We perform an experiment to measure the decay rate of fast moving muons. We find that it agrees with the theory. Therefore we conclude that spacetime does indeed have the symmetries. What could be more scientific than that? That is the essence of the scientific method.azoulay said:"but from nature of spacetime itself" This is NOT true science, this is magical non-sense, easy way out, I'm not sure what's going on but I have to come up with something science.
azoulay said:If Science has to invent words, concepts, difficult mathematical structures, irrational thinking, new definitions that are incomprehensible for anyone expect for a science or math PhD, then for sure, science is wrong about what it has to offer. Wouldn't you think so ?
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I respect all of you guys, I love science myself very much but let's agree on one thing: science is getting more and more difficult to understand. Doesn't that ring a bell that it's not going in the right direction ?
azoulay said:If Science has to invent words, concepts, difficult mathematical structures, irrational thinking, new definitions that are incomprehensible for anyone except for a science or math PhD, then for sure, science is wrong about what it has to offer. Wouldn't you think so