A question about the present!

[JohnLesser]

 

 

But they are not "in the past".

 

 

The two twins can still talk to each other. There isn't a 5 minute delay before twin 1 hears twin 2.

Sound has to travel, there is a delay .

[DrmDoc]

Time is a measurement, I am not sure we experience time but rather observe the affects of it.

 

You referred to objects in time dilation as being behind your time, as if in the past. Observations of objects in time dilation are not observations of those objects in your temporal past, they are observations of time passing more slowly for those objects than it does for you.

Edited April 2, 2017 by DrmDoc

[JohnLesser]

 

You referred to objects in time dilation as being behind your time, as if in the past. Observations of objects in time dilation are not observations of those objects in your temporal past, they are observations of time passing more slowly for those objects than it does for you.

With due respect you are not thinking about what you are writing and saying.

 

time passes slowly , so the clock will show a lesser time than the ground state clock. Are you saying if the clock showed a shorter length of time it would still be in the present?

[Strange]

Sound has to travel, there is a delay .

 

 

Are you deliberately missing the point?

 

One of the twins clock reads a different time and she has aged less. BUT IS NOT IN THE PAST.

time passes slowly , so the clock will show a lesser time than the ground state clock. Are you saying if the clock showed a shorter length of time it would still be in the present?

 

Yes.

[Janus]

(red color added by me)

If I understand correctly, you are observing an object traveling faster than light. The object made 1light hour distance in 15 min. Is that possible?

Yes, there is nothing in Relativity that forbids Such "apparent" superluminal velocities. Just because you visually see the clock approaching at a greater than c speed, does not mean that you would consider it as moving faster than c.

Do not conflate "what you see" with "what is happening". You can use "what you see" (along with other information) to determine "what is happening", but they are not the same thing.

In this case, you "see" the clock crossing 1 light hr of distance in 15 min, but that is just due to the fact both the light showing the clock 1 light hr away and the clock leave the same point at the same time, and the light beats the clock to you by fifteen minutes. Thus you "see" the trip compressed into 15 min. But since you know that this light took an hour to get to you, you know that both the light and clock left 1 hr before you first see the light from the clock.

If you see the clock leave when your clock reads 1:00, you know that the clock and light both left when your clock read 12:00, and since the clock arrives when your clock reads 1:15, the clock took 1 hr 15 min to reach you, and traveled at 0.8c relative to you, regardless of the fact that you "see" the clock coming at you you much faster

[JohnLesser]

 

 

Are you deliberately missing the point?

 

One of the twins clock reads a different time and she has aged less. BUT IS NOT IN THE PAST.

 

Yes.

So you are saying time does not slow down.

 

A short time line can not be synchronous to a greater length.

 

If they both remained in the present then you will have to define absolute time?

Edited April 2, 2017 by JohnLesser

[Strange]

Yes.

 

 

Or, at least, they can be.

So you are saying time does not slow down.

 

 

No.

If they both remained in the present then you will have to define absolute time?

 

 

No.

[JohnLesser]

 

 

Or, at least, they can be.

 

 

No.

 

 

No.

So then you agree twin 2 ''drifts'' into the past?

 

I wish you would please stop being contradictory.

[Strange]

Let's look at distance rather than time. It may be less confusing for you.

 

Two cars set off on different routes from X to Y, but they leave and arrive together. One car (A) drives a straight line between X and Y. The other (B) takes a longer circular route.

 

A watches B's odometer and sees that it is incrementing miles more slowly than his (it is "dilated" with respect to his).

 

When they both arrive at Y they compare "clocks" (odometers) and B's odometer is reading more miles travelled. Lets say 10 miles more. This doesn't mean that he is 10 miles ahead of A. They are at the same place. It just means he took a different journey through space-time.

 

But they still end up in the same place at the same time.

So then you agree twin 2 ''drifts'' into the past?

 

No.

 

 

I wish you would please stop being contradictory.

 

It only appears contradictory because you don't understand.

[JohnLesser]

Let's look at distance rather than time. It may be less confusing for you.

 

Two cars set off on different routes from X to Y, but they leave and arrive together. One car (A) drives a straight line between X and Y. The other (B) takes a longer circular route.

 

A watches B's odometer and sees that it is incrementing miles more slowly than his (it is "dilated" with respect to his).

 

When they both arrive at Y they compare "clocks" (odometers) and B's odometer is reading more miles travelled. Lets say 10 miles more. This doesn't mean that he is 10 miles ahead of A. They are at the same place. It just means he took a different journey through space-time.

 

But they still end up in the same place at the same time.

 

No.

 

 

It only appears contradictory because you don't understand.

Oh , I understand, to arrive at the same time their journey time would have to be synchronous, the curved vector travelled needing more speed to compensate for extra distance to retain synchronisation.

I hardly ''see'' how that is relevant though.

[DrmDoc]

With due respect you are not thinking about what you are writing and saying.

 

time passes slowly , so the clock will show a lesser time than the ground state clock. Are you saying if the clock showed a shorter length of time it would still be in the present?

 

With equal respect, you are not giving full consideration to what any of us here are clearly conveying. If you were to observe a clock in a time dilation bubble from outside of that bubble, you would observe that time dilated clock moving slowly compared to your ground clock. If your were to observe a ground clock from inside a dilation bubble, you would observe that outside ground clock hands moving more rapidly than your clock inside the time dilations. In either case, you would not be observing either past or future--you would merely be observing variations in the speed at which time passes. Further still, time dilation and observations of distant objects do not regard the same effect.

Edited April 2, 2017 by DrmDoc

[JohnLesser]

 

With equal respect, you are not giving full consideration to what any of us here are clearly conveying. If you were to observe a clock in a time dilation bubble from outside of that bubble, you would observe that time dilated clock moving slowly compared to your ground clock. If your were to observe a ground clock from inside a dilation bubble, you would observe that outside ground clock hands moving more rapidly than your clock inside the time dilations. In either case, you would not be observing either past or future--you would merely be observing variations in the speed at which time passes. Further still, time dilation and observations of distant objects do not regard the same effect.

Quite clearly you are being contradictory, in one breath saying that time slows down then in another breath saying it does not.

 

If time was passing slower for me, I would be still in 2016 for example.

Edited April 2, 2017 by JohnLesser

[DrmDoc]

Quite clearly you are being contradictory, in one breath saying that time slows down then in another breath saying it does not.

 

If time was passing slower for me, I would be still in 2016 for example.

 

I'll give it one last try. Observing an object in a time dilations bubble is not observing an object in your relative past. It's observing the viscus effects of time dilation on that objects motion and aging, which slows relative to your non-viscus temporal state. However, observing objects at a distance is indeed an observation of that object's past state, which is merely observing light from a distant object that has traveled a measure of time to reach your observation. What you would be observing isn't the object itself but rather it's light delayed and aged by the time it took to reach your position of observation.

[JohnLesser]

 

I'll give it one last try. Observing an object in a time dilations bubble is not observing an object in your relative past. It's observing the viscus effects of time dilation on that objects motion and aging, which slows relative to your non-viscus temporal state. However, observing objects at a distance is indeed an observation of that object's past state, which is merely observing light from a distant object that has traveled a measure of time to reach your observation. What you would be observing isn't the object itself but rather it's light delayed and aged by the time it took to reach your position of observation.

So time does not really slow down?

 

Again contradiction

Edited April 2, 2017 by JohnLesser

[DrmDoc]

So time does not really slow down?

 

Again contradiction

 

No contradiction; time dilation and observing objects at a distance are not the same and do not regard the same effect.

[swansont]

This thread has been a goid example why physics veers away from qualitative descriptions and vague terminology.

 

Time passage is relative. But at no point does anything travel backward in time, i.e. into the past. If that's what you think, you're missing something, and the focus should be on what your misconception is.

[JohnLesser]

This thread has been a goid example why physics veers away from qualitative descriptions and vague terminology.

 

Time passage is relative. But at no point does anything travel backward in time, i.e. into the past. If that's what you think, you're missing something, and the focus should be on what your misconception is.

Maybe you are missing something.

 

I will try to explain to you by using a calendar.

 

Twin 1 ground state marks 1 day every 24 hrs of time elapsed.

 

Twin 2 in motion with a slower rate of time marks one day every 24 hrs elapsed.

 

Twin two marks 1 day, later than twin one. Twin ones days are shorter than twin 2's days.

Edited April 3, 2017 by JohnLesser

[Endy0816]

You won't see someone else marking off a day in what you consider a day if you are in a different frame.

[DrmDoc]

Maybe you are missing something.

 

I will try to explain to you by using a calendar.

 

Twin 1 ground state marks 1 day every 24 hrs of time elapsed.

 

Twin 2 in motion with a slower rate of time marks one day every 24 hrs elapsed.

 

Twin two marks 1 day, later than twin one. Twin ones days are shorter than twin 2's days.

 

Twin two marks 1 day later than twin one because twin two's days (24 hrs.) are longer relative twin one's days. Twin two perceives his days as normal time although twin one see twin two's days as longer than his. Conversely, twin two perceives twin one's days as shorter than his although twin one views his day as normal time also. Twin two isn't in the past, he is merely experiencing elongated (dilated) time relative to twin one.

Edited April 3, 2017 by DrmDoc

[Strange]

Oh , I understand, to arrive at the same time their journey time would have to be synchronous, the curved vector travelled needing more speed to compensate for extra distance to retain synchronisation.

I hardly ''see'' how that is relevant though.

 

 

It is relevant because it shows you can take a longer path but still arrive at the same place.

 

Similarly, you can take a longer path through space-time and still end up in the present.

 

This "Twin Paradox" experiment has been done, you know. It didn't end up with one of the aircraft in the past.

Maybe you are missing something.

 

I will try to explain to you by using a calendar.

 

Twin 1 ground state marks 1 day every 24 hrs of time elapsed.

 

Twin 2 in motion with a slower rate of time marks one day every 24 hrs elapsed.

 

Twin two marks 1 day, later than twin one. Twin ones days are shorter than twin 2's days.

 

 

But he still not travelling into the past.

[Manticore]

No it isn't. Just because the light we see from a distant object originated in the past does not mean that we consider it as being in the past when we see that light.

If a clock is 1 light hr from me and I, at this moment, see it reading 12:00, this does not mean that I think it reads 12:00 at this moment, but that it read 12:00 one hr ago. Assuming the clock runs at the same rate as my own, then according to me, right now that clock reads 1:00.

With Relativity, if the clock is moving relative to me, I just can't assume that it ticks at the same rate as mine. So for example if the clock starts where I am, with both my clock and it reading 12:00, and that clock recedes from me at 0.8c, I will see the clock run 1/3 as fast as mine. After 1 1/4 hrs, it will be 1 light hour away. I won't see this event happen for another hr, so I will spend 2 1/4 hrs watching it recede, all the time ticking 1/3 as fast as my clock. Thus when I see it reach the distance of 1 light hr, it will see it reading 12:45

I also know that it actually took 1hr 15 min to actually get there, and 45 min/ 1 hr 15 min = 0.6, so that means that the clock ticked at a rate 0.6 as fast as mine. This factor of 0.6 is the time dilation.

 

You can also work it the other way. We can assume that the clock starts 1 light hour away while reading the same time as my clock and is coming at me at 0.8c. It will still take 1 hr 15 min to reach me. I however won't see it leave until my clock reads 1:00, thus it arrives 15 min after first see it leave the point 1 light hr away. During that 15 min I see it ticking 3 times as fast as my clock, and see it tick off 45 min and reads 12:45 upon arrival. I also know that it actually left 1 hr 15 min ago by my clock. So once again we have it ticking off 45 min while my clock ticked off 1 hr 15 min, and it ticked 0.6 as fast as my clock.

that has to be the most beautifully concise explanation of time dilation I have ever come across. I wish my lecturers (and textbooks) when I studied Astrophysics could have put it over half so well.

[madmac]

A general observation.

Surely we all agree that there is no such thing as time dilation -- it is merely a change or difference in ticking.

I think that Einstein goes one step further -- i think he says there is no such thing as time -- hencely no such thing as time dilation.

 

Surely we all agree that time passes at the same rate for all, all the time.

We all sense that our inner clocks tick at the same rate, all the time, no matter what is happening to our wrist watches.

If u whirl your wristwatch around & around (in the vert plane say), Einsteinians would say that it ticks slower.

But time must surely seem to pass at the same rate for all of us, no matter whether our watch is good or slow or fast, no matter whether we whirl our arms (with the wristwatch), no matter which twin we are.

 

But getting back to JohnLesser's OP.

Would it be true that the present only exists locally because of the nature of light and its finite speed only allowing delayed images of observation?

 

I reckon that this question could be well debated by a deaf person (or not deaf) & a blind person.

 

Also, imagine how our world would look (& the effect on the present) if sound travelled at c, & light travelled at Mach1.

Edited April 3, 2017 by madmac

[Strange]

that has to be the most beautifully concise explanation of time dilation I have ever come across. I wish my lecturers (and textbooks) when I studied Astrophysics could have put it over half so well.

 

 

Janus's explanations are always a pleasure to read.

A general observation.

Surely we all agree that there is no such thing as time dilation -- it is merely a change or difference in ticking.

 

Or, in other words, time dilation.

 

 

 

I think that Einstein goes one step further -- i think he says there is no such thing as time -- hencely no such thing as time dilation.

 

Citation needed.

 

 

 

Surely we all agree that time passes at the same rate for all, all the time.

 

As seen by them; i.e. proper time.

 

However, it doesn't [necessarily] pass at the same rate as seen by someone else.

 

 

But getting back to johnlesser's OP -- what if the observer is blind????

 

Why would that make any difference?

[mistermack]

The problem I have with that explanation, (not disputing it, but getting my head round it) is that the assumption seems to be made that I am stationary, and it's the other clock that is moving. But according to SR, it's equally valid to assume that the other clock is stationary, and I am moving. So from his viewpoint, my clock ticked 0.6 as fast as HIS clock.

 

That is the twin paradox, both clocks can't run at 0.6 x the rate of the other.

 

I have read the various explanations of the twin paradox, and struggle to make them work in my head.

The role of acceleration required to make two twins separate and return to each other makes the most sense.

But then you have the example of a third "twin" meeting the second one halfway, and taking the reading of the clock back to the first twin, eliminating acceleration from the event entirely.

 

So that's where I struggle. For one clock to ACTUALLY run slower than another, in non-accelerated motion, there needs to be an actual difference between the two states of inertial motion. Not just a relative difference.

[swansont]

Maybe you are missing something.

 

I will try to explain to you by using a calendar.

 

Twin 1 ground state marks 1 day every 24 hrs of time elapsed.

 

Twin 2 in motion with a slower rate of time marks one day every 24 hrs elapsed.

 

Twin two marks 1 day, later than twin one. Twin ones days are shorter than twin 2's days.

 

 

I'm not missing anything.

 

After some interval, Twin 1's calendar reads April 3, while twin 2's reads March 3. Neither one is in the other's past, other than the normal delay from communication not being instant. If they observe a remote equidistant phenomenon, they will disagree on when they observed it, but what doesn't happen is that the "slow" twin is a month behind in experiencing this type of phenomenon. She experiences it on March 3 rather than April 3.

 

"Past" and "present" are not the right tools to discuss relativity, as I mentioned earlier. You use t₀ t₁ t₀' and t₁', for example.

The problem I have with that explanation, (not disputing it, but getting my head round it) is that the assumption seems to be made that I am stationary, and it's the other clock that is moving. But according to SR, it's equally valid to assume that the other clock is stationary, and I am moving. So from his viewpoint, my clock ticked 0.6 as fast as HIS clock.

 

That is the twin paradox, both clocks can't run at 0.6 x the rate of the other.

 

I have read the various explanations of the twin paradox, and struggle to make them work in my head.

The role of acceleration required to make two twins separate and return to each other makes the most sense.

But then you have the example of a third "twin" meeting the second one halfway, and taking the reading of the clock back to the first twin, eliminating acceleration from the event entirely.

 

So that's where I struggle. For one clock to ACTUALLY run slower than another, in non-accelerated motion, there needs to be an actual difference between the two states of inertial motion. Not just a relative difference.

 

 

The third twin can't do this without accelerating. Once you insist that one thing is ACTUALLY happening you are declaring a preferred frame, and these do not exist in relativity. You can't do an experiment that gives a special result in one frame as compared to another.