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Why is Time so controversial?
Posted: 11 November 2011 03:29 AM   [ Ignore ]   [ # 46 ]
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dougsmith - 10 November 2011 11:45 AM
StephenLawrence - 10 November 2011 11:16 AM

But we experience ourselves to be 3 dimensional. We experience it being now for us, not yesterday, not tomorrow. We experience ourselves being wholly present today, not as part of a spacetime worm.

From a scientific point of view it is no more today than 5,000 years ago.

What do you mean? “It’s no more today than 5,000 years ago” is covertly indexical. You mean to say, “It’s no more today right now than 5,000 years ago”? But that’s false. Right now (spoken “today”) it is today.

When you say “It’s no more today than 5,000 years ago” you’re speaking from a vantage point outside of time, as it were. That’s not the vantage point we typically use when we’re saying “It’s today”. (Or perhaps better, “It’s Thursday today.”)

I’m not sure. There are lots of vantage points and yet it seems one is privelaged over the others in a way that the above doesn’t satisfy. Perhaps not.

StephenLawrence - 10 November 2011 11:16 AM

Sometimes, often in fact, we make decisions that are bad for us today but good for us tomorrow. Why do we do it? We don’t just do it because we care about our future selves, we do it because we think we will be there! We think this thing that is me now will move along into the future and experience the reward.

That’s at odds with science, or so it seems.

I’m not prepared to bet on science in this case, is anybody, really?

Well, science is all about causality, and the causal chain leading from past to future. So none of that is at odds with science. It’s just that there’s no such thing as the special “now” in science. All times are “now” from their own vantage point, just like all places are “here” from their own vantage point.

This misses the point. If I don’t fix my customers bike today, I will suffer the consequences tomorrow. When I say this I’m saying me today will be there. It’s the same me, not a different part of me. There is a difference with merely caring about my future self and being helpful now out of sympathy and believing I, as in I who is making the decision now, will be there.

Of course, all of the experiences of which George speaks are due to brain activity of one sort or another, and so in some sense are objective as well. But it’s a different sense than the sense we’re speaking of with “objective time”.

Yes.

What I was trying to get at (badly) was in order to experience time traveling into the future, as we seem to, there needs to be a subject of that experience.

I don’t see how something which is four dimensional can be.

Stephen

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Posted: 11 November 2011 04:45 AM   [ Ignore ]   [ # 47 ]
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Just a few reactions…

dougsmith - 10 November 2011 09:56 AM

Well, I think however we approach the subject of time we should be careful to distinguish experienced time, which has the odd properties that George alludes to, from objective time. The latter is what the physics stuff from Einstein is about.

Objective time that does not match with our daily experience, not even with our measurements?

domokato - 10 November 2011 11:03 AM

Next question: why does entropy do that!

I’ve heard physicists say that time is symmetrical, that if you reverse time, the equations would still hold. But obviously they don’t, for entropy, and for forces like gravity. (?)

Does entropy do that? I notice how physicists very often give the answer ‘entropy’ when it is about explaining the arrow of time, and then just go on doing their work. The few exceptions on this rule never give a definite answer, there stay too many problem with that answer. One must not forget that entropy is about statistics. Systems tend to develop in the direction of more entropy, but they do not necessarily do that. Now this statistical tendency is extremely strong, so we would wonder immediately when a system we see in daily life would develop in a direction of less entropy (the spilled water jumping spontaneously into the glass), but there is no non-statistical physical law that forbids this process. With that the question of gravity is answered too: there is no arrow of time in gravity.

dougsmith - 10 November 2011 11:11 AM

What seems like it’s going forward in time is only a time-slice of you, you-now.

Yes. But doesn’t this ‘time-slice’ can only move forward in time? That is the arrow of time. The ‘objective’ view from ‘outside spacetime’ does not exist. Do not forget: the physicist’s time in relativity theory is a mathematical construct. As a parallel, take this example of the construction of an ideal reflection of a ball with a wall:

?ACT=27&fid=31&aid=610_bHa3DJTzXG0DH0rWlhdI&board_id=1

Would you say that the virtual object really exists? Would you deny that the geometrical construction works? Now, it is clear that relativistic calculations work. But does that mean that ‘virtual time’ really exists?

dougsmith - 10 November 2011 11:50 AM

I’ve never quite understood how entropy solves the problem of time’s arrow. It seems a correlation rather than an explanation.

Exactly…

traveler - 10 November 2011 01:36 PM

An atomic clock traveling in a jet runs more slowly than one sitting on the ground.
That confuses me.

The time an earthly observer see on the clock of the plane is slower than his earthly clock. An observer in the plane sees it the other way round: the clock on earth seems to be slower than his clock on board of the plane. That is because earth and plane move against each other. The other movements of the earth play no role. As this sounds paradoxical (that for both observers the clock of the other one is slower), this paradox disappears if you realise that if the plane is on the ground again it must have accelerated twice (braking also counts as accelerating, as negative acceleration). See the twin paradox for details.

Write4U - 10 November 2011 08:19 PM

I am asserting that space has 3 coordinates and time is created when an object moves between at least two of these coordinates.

We had this long ago… Without time, there cannot be change. Logically the opposite might also be true, but we cannot know. When there is an observer, there is change.

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Posted: 11 November 2011 04:56 AM   [ Ignore ]   [ # 48 ]
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StephenLawrence - 11 November 2011 03:29 AM

This misses the point. If I don’t fix my customers bike today, I will suffer the consequences tomorrow. When I say this I’m saying me today will be there. It’s the same me, not a different part of me. There is a difference with merely caring about my future self and being helpful now out of sympathy and believing I, as in I who is making the decision now, will be there.

I’m not sure I get your point. You-today is a different part of you from you-tomorrow. They’re both temporal parts of you. It’s just like you are worried about your finger, a physical (spatial) part of you, which is a different part of you from your toe.

StephenLawrence - 11 November 2011 03:29 AM

What I was trying to get at (badly) was in order to experience time traveling into the future, as we seem to, there needs to be a subject of that experience.

I don’t see how something which is four dimensional can be.

Perhaps what you’re after is that that ‘subject of experience’ is a temporal part of you. I dunno.

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Posted: 11 November 2011 05:04 AM   [ Ignore ]   [ # 49 ]
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GdB - 11 November 2011 04:45 AM

Just a few reactions…

dougsmith - 10 November 2011 09:56 AM

Well, I think however we approach the subject of time we should be careful to distinguish experienced time, which has the odd properties that George alludes to, from objective time. The latter is what the physics stuff from Einstein is about.

Objective time that does not match with our daily experience, not even with our measurements?

I didn’t mean to imply that. Surely our experience (roughly) matches measurements most of the time. But as George pointed out, there are times when they don’t. It’s like visual or auditory illusions: just because they happen sometimes or can be manufactured doesn’t mean that our eyes and ears typically provide us bad information about the world.

GdB - 11 November 2011 04:45 AM
dougsmith - 10 November 2011 11:11 AM

What seems like it’s going forward in time is only a time-slice of you, you-now.

Yes. But doesn’t this ‘time-slice’ can only move forward in time? That is the arrow of time. The ‘objective’ view from ‘outside spacetime’ does not exist. Do not forget: the physicist’s time in relativity theory is a mathematical construct. As a parallel, take this example of the construction of an ideal reflection of a ball with a wall:

?ACT=27&fid=31&aid=610_bHa3DJTzXG0DH0rWlhdI&board_id=1

Would you say that the virtual object really exists? Would you deny that the geometrical construction works? Now, it is clear that relativistic calculations work. But does that mean that ‘virtual time’ really exists?

I’m not sure I understand your point. Here the virtual object does not exist, except as a figment in the viewer’s mind. But the (spatio-)temporal effects of relativity are quite thoroughly verified. They aren’t virtual, nor are they merely mathematical constructs.

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Posted: 11 November 2011 05:17 AM   [ Ignore ]   [ # 50 ]
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dougsmith - 11 November 2011 04:56 AM
StephenLawrence - 11 November 2011 03:29 AM

This misses the point. If I don’t fix my customers bike today, I will suffer the consequences tomorrow. When I say this I’m saying me today will be there. It’s the same me, not a different part of me. There is a difference with merely caring about my future self and being helpful now out of sympathy and believing I, as in I who is making the decision now, will be there.

I’m not sure I get your point. You-today is a different part of you from you-tomorrow. They’re both temporal parts of you. It’s just like you are worried about your finger, a physical (spatial) part of you, which is a different part of you from your toe.

I think it’s more like my toe being concerned for my finger’s well being.

StephenLawrence - 11 November 2011 03:29 AM

What I was trying to get at (badly) was in order to experience time traveling into the future, as we seem to, there needs to be a subject of that experience.

I don’t see how something which is four dimensional can be.

Perhaps what you’re after is that that ‘subject of experience’ is a temporal part of you. I dunno.

But that’s exactly the point, it appears that a temporal part can’t experience time traveling into the future because it stays at the time it’s at.

edit: I suppose what you need is two or more confused temporal parts.  grin

Stephen

[ Edited: 11 November 2011 05:24 AM by StephenLawrence ]
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Posted: 11 November 2011 06:19 AM   [ Ignore ]   [ # 51 ]
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traveler - 10 November 2011 01:36 PM

According to Einstein, it is physical motion through space that affects time. That’s why there is really no space and no time; just spacetime because they are. Motion adds to the space component and subtracts from the time component. An atomic clock traveling in a jet runs more slowly than one sitting on the ground.

That confuses me. Why? Because the Earth is traveling over 66,000 MPH around the sun and also spinning at about 900 MPH (at a 30 degree latitude). So it seems that a jet traveling in a direction counter to the earth’s, then it is going slower and the clock should speed up. But the experiments always show the clocks in jets slowing down.

But the plane also travels at 66,000 around the sun and unless you want to escape earth orbit and fly away from the earth you will be traveling at 66,000 around the sun also. As long as we stay in orbit each would gain a little on the one side and lose a little on the other side. So we are not dealing with speeds relative to the sun, we are dealing with speeds relative to the earth.
Thus a plane traveling counter to earths’s rotation at 1000 mph would be traveling relatively 1900 miles faster than your stationary twin and arrive at a given rendez vous well ahead of the stationary twin and at a younger age than your twin will be when he arrives later (and older) than you were when you arrived at the rendez vous. In this example it would not be a case of who arrived first, but how old each was when they arrived at the rendez vous.
Perhaps this is why :

dougsmith
It says that if one twin stays on Earth and the other accelerate at a high percentage of the speed of light towards Alpha Centauri, then accelerates back towards Earth, the twin that traveled at high acceleration will return younger than the twin who stayed home. This is because the twin who accelerates has a clock that ticked relatively slower. Similar issues exist about length in direction of acceleration: the twin that accelerated would have been relatively shorter in the direction of acceleration than the twin that remained behind. This relative difference would have disappeared when the twin ceased relative acceleration, however the difference in apparent age would remain.

But to get this “acceleration” clear in my head (in its simplest form).

If I travel at a steady 60 mph and my twin travels in the same direction at a steady 40 mph, I am (relatively) acceleration away from my twin at 20 mph even though my speed remains at a steady 60 mph, correct?
Thus one does not have constantly increase their own speed to still accelerate away from a twin which travels at a constant but slower speed or is at rest. (in this example I am ignoring other factors for simplicity).

[ Edited: 11 November 2011 06:27 AM by Write4U ]
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Posted: 11 November 2011 07:05 AM   [ Ignore ]   [ # 52 ]
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dougsmith - 11 November 2011 05:04 AM

I’m not sure I understand your point. Here the virtual object does not exist, except as a figment in the viewer’s mind. But the (spatio-)temporal effects of relativity are quite thoroughly verified. They aren’t virtual, nor are they merely mathematical constructs.

Sure, I am the last to deny the results of relativity. But I have some reservations about using the term absolute time, and I think the parallel with my geometry example holds. The virtuality of ‘absolute time’ is not a denial of the correct results of relativity, as the virtuality of the ‘virtual object’ is not a denial of the correct construction of the trajectory of the ball. Why should relativistic time, being i.t (i being the imaginary i), be objective time?

This time does not contain 2 essential attributes of real time: that it has one single direction, and exactly this ‘shifting now’. Physics is perfectly able to match ‘absolute time’ with our experienced time, (e.g. the prediction of the exact beginning of a moon eclipse, somebody say ‘and the eclipse starts one second from .... NOW!’), but it cannot explain what the physical meaning of ‘now’ is in terms of absolute time. And I agree with you, entropy seems more a correlation than an explanation. But entropy is not a constitutive element of relativity.

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Posted: 11 November 2011 07:28 AM   [ Ignore ]   [ # 53 ]
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Write4U - 11 November 2011 06:19 AM

If I travel at a steady 60 mph and my twin travels in the same direction at a steady 40 mph, I am (relatively) acceleration away from my twin at 20 mph even though my speed remains at a steady 60 mph, correct?

No. Acceleration is a change in velocity over time. If you and your twin are traveling at a steady rate of 20 mph away from each other, neither of you is accelerating at all.

Further, if the universe only contains you and your twin, the only fact of the matter is that you are traveling away from each other at 20 mph. The 60 and 40 mph stuff don’t have anything with which they would be relative to, and so are meaningless. OTOH if you and your twin are floating in space near the Moon, then sure, you could be traveling a steady 60 mph relative to the Moon and your twin could be traveling 40 mph relative to the Moon and then if you were going in the same direction, you would be traveling (NOT accelerating) at 20 mph away from your twin.

Put it another way: velocity is gauged in miles per hour or meters per second. Acceleration is gauged in miles per hour per hour, or mph squared. (Or meters per second per second, otherwise known as m/s^2).

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Posted: 11 November 2011 07:31 AM   [ Ignore ]   [ # 54 ]
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GdB - 11 November 2011 07:05 AM
dougsmith - 11 November 2011 05:04 AM

I’m not sure I understand your point. Here the virtual object does not exist, except as a figment in the viewer’s mind. But the (spatio-)temporal effects of relativity are quite thoroughly verified. They aren’t virtual, nor are they merely mathematical constructs.

Sure, I am the last to deny the results of relativity. But I have some reservations about using the term absolute time, and I think the parallel with my geometry example holds. The virtuality of ‘absolute time’ is not a denial of the correct results of relativity, as the virtuality of the ‘virtual object’ is not a denial of the correct construction of the trajectory of the ball. Why should relativistic time, being i.t (i being the imaginary i), be objective time?

This time does not contain 2 essential attributes of real time: that it has one single direction, and exactly this ‘shifting now’. Physics is perfectly able to match ‘absolute time’ with our experienced time, (e.g. the prediction of the exact beginning of a moon eclipse, somebody say ‘and the eclipse starts one second from .... NOW!’), but it cannot explain what the physical meaning of ‘now’ is in terms of absolute time. And I agree with you, entropy seems more a correlation than an explanation. But entropy is not a constitutive element of relativity.

Sorry, I’m still not getting your point, or even if we’re disagreeing. “Objective time” is the stuff that’s measured by an accurate clock. When someone says that ‘time flies when you’re having fun’, or ‘a watched pot never boils’, he’s not talking about this sort of objective time. He’s talking about felt or perceived or subjective time. Clearly the clock is ticking at the same rate whether you’re having fun or whether you’re waiting for the water to boil.

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Posted: 11 November 2011 08:07 AM   [ Ignore ]   [ # 55 ]
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I am just saying that the time in ‘objective spacetime’ is better called virtual time, instead of the time measured by a clock. I was not reacting at subjective time.

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Posted: 11 November 2011 08:44 AM   [ Ignore ]   [ # 56 ]
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As Doug mentioned, acceleration is reqd for time travel (although the NOVA program did not make that clear). And as GdB mentioned, the virtual time has to be translated into actual time in order to be useful. These things cannot be explained adequately in a forum discussion, BUT there is a nice and fairly succinct (given the topic!) paper that explains all of this quite well IMO. If you have had calculus, you should be able to follow it pretty easily. LINK (pdf)

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Posted: 11 November 2011 11:35 AM   [ Ignore ]   [ # 57 ]
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GdB - 11 November 2011 04:45 AM
domokato - 10 November 2011 11:03 AM

Next question: why does entropy do that!

I’ve heard physicists say that time is symmetrical, that if you reverse time, the equations would still hold. But obviously they don’t, for entropy, and for forces like gravity. (?)

Does entropy do that? I notice how physicists very often give the answer ‘entropy’ when it is about explaining the arrow of time, and then just go on doing their work. The few exceptions on this rule never give a definite answer, there stay too many problem with that answer. One must not forget that entropy is about statistics. Systems tend to develop in the direction of more entropy, but they do not necessarily do that. Now this statistical tendency is extremely strong, so we would wonder immediately when a system we see in daily life would develop in a direction of less entropy (the spilled water jumping spontaneously into the glass), but there is no non-statistical physical law that forbids this process. With that the question of gravity is answered too: there is no arrow of time in gravity.

Hm, not quite sure I understand how there is no arrow of time in gravity. With a normal arrow of time, gravity pulls. Reverse it, and gravity pushes.

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Posted: 11 November 2011 12:31 PM   [ Ignore ]   [ # 58 ]
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domokato - 11 November 2011 11:35 AM

Hm, not quite sure I understand how there is no arrow of time in gravity. With a normal arrow of time, gravity pulls. Reverse it, and gravity pushes.

Well, the authoritative answer is ‘otherwise some physicist would have mentioned it’.

The more imaginative answer is: nothing in the law of gravity forbids that accidentally many small particles on earth move to a certain place, and blast from this place a meteor into space.

Less fanciful is that in a planetarium one could turn the clock in the opposite direction, and the movements you see then are all perfectly physically possible. In both cases, gravity is still attractive.

See here and here for more details.

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Posted: 11 November 2011 04:08 PM   [ Ignore ]   [ # 59 ]
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Oh oh, i get it. Thanks

It can be thought of as what happens after a bounce (things do go up sometimes, duh!).

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Posted: 11 November 2011 10:19 PM   [ Ignore ]   [ # 60 ]
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A few tardy observations:

One of Einstein’s big ideas was the notion that reality is defined by the act of measuring it. Thus, a straight line in space is defined by the path of a photon (you look down the length of the ruler to determine whether it is straight).

Cute realization: space cannot exist without matter, because with no matter, we have no way of identifying a point in space. There’s nothing to put your ruler on to measure with. With two particles of matter, we can define a distance. We need at least three particles of matter to define 3-space.

Same thing goes with time: you need events to measure time. Without events, you don’t have a starting and ending point to measure a time interval with.

None of this tells us anything about the intrinsic nature of time or space. There is no such thing. “To measure is to know”—conversely, the theoretically immeasurable is unknowable.

Lastly, time gets caught up in Second Thermo and Uncertainty Principle. About 35 years ago I realized that the Uncertainty Principle and Second Thermo are two expressions of the same concept. I came to believe that information is the fundamental component of the universe, an idea that is now gaining some currency among physicists. However, I now believe that the fundamental dimension of the universe is not information but bandwidth; time and information are derivative components of bandwidth.

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