How time dilation occurs

[Jay-qu]

Whilst it is true mainstream physics states that high velocity will cause time dilation there cannot be any experiment on time dilation that does not involve an element of acceleration.

 

Tony

Uclock, this is the 2nd thread you have brought this idea into, I suggest that if you wish to discuss the matter you start your own thread.

[Uclock]

I already have but it appears no one wishes to comment on my concept of three dimensional spacetime.

 

Tony

[ALADIN]

Ok guys I am a bit confused about this whole matter.

 

I understand that if I am standing on earth and you fly away in a speeding spaceship for one year and then back for one year, let's say the equiavalent of 20 years pass on earth.

 

That's great.

 

And then I realize that if I could be looking at your watch it would be moving slower than mine.

 

That's great too.

 

The part that throws me off is that it also states that if throughout your trip you were looking at my watch, then it would seem as if MY watch is the one moving slower.

 

But if that's the case, and you continued to view my watch throughout your entire trip, how could you say that 20 years have gone by for me when you got back, and you not notice it(because it was MY watch that was moving slower)?

 

In other words, from your point of refference only one year went by, and since my watch was moving slower, from your point of refference LESS then one year would have to have gone by for me.....yet when you got back you found that 20 years went by. HOW is this possible?

[Uclock]

Aladin

 

Ok guys I am a bit confused about this whole matter.

 

I understand that if I am standing on earth and you fly away in a speeding spaceship for one year and then back for one year, let's say the equiavalent of 20 years pass on earth.

 

That's great.

 

And then I realize that if I could be looking at your watch it would be moving slower than mine.

 

That's great too.

 

The part that throws me off is that it also states that if throughout your trip you were looking at my watch, then it would seem as if MY watch is the one moving slower.

 

But if that's the case, and you continued to view my watch throughout your entire trip, how could you say that 20 years have gone by for me when you got back, and you not notice it(because it was MY watch that was moving slower)?

 

In other words, from your point of refference only one year went by, and since my watch was moving slower, from your point of refference LESS then one year would have to have gone by for me.....yet when you got back you found that 20 years went by. HOW is this possible?

 

Welcome to the world of Einstein’s relativity. What you have described is the well known twin paradox thought experiment. IMHO the only difference between the person who stays on Earth and the one who goes off into deep space is that the traveller in deep space has to undergo acceleration but according to Einstein’s relativists this is not the cause for the time difference. I have yet to here a satisfactory explanation but I have not yet come across one.

 

Tony

[Jay-qu]

Welcome to the world of Einstein’s relativity. What you have described is the well known twin paradox thought experiment. IMHO the only difference between the person who stays on Earth and the one who goes off into deep space is that the traveller in deep space has to undergo acceleration but according to Einstein’s relativists this is not the cause for the time difference. I have yet to here a satisfactory explanation but I have not yet come across one.

 

Tony

 

Well then I cant say you have looked terribly hard..

 

Although special relativity predicts differential aging for the traveling twin as compared to the stay-at-home twin, it is not a paradox in the sense of an inherently contradictory result. The perception of paradox, referred to as the twin paradox (sometimes called the 'clock paradox') is caused by the error of assuming that relativity implies that only relative motion between objects should be considered in determining clock rates. The result of this error is the prediction that upon return to Earth, each twin sees the other as younger -- which is clearly impossible.

[Uclock]

Jay-qu

 

Originally Posted by wiki

Although special relativity predicts differential aging for the traveling twin as compared to the stay-at-home twin, it is not a paradox in the sense of an inherently contradictory result. The perception of paradox, referred to as the twin paradox (sometimes called the 'clock paradox') is caused by the error of assuming that relativity implies that only relative motion between objects should be considered in determining clock rates. The result of this error is the prediction that upon return to Earth, each twin sees the other as younger -- which is clearly impossible.

 

And that is supposed to be an explanation?

 

Velocity is relative and the twin paradox still holds.

 

Tony

[Farsight]

Kalesh: I know how and why time dilation occurs. See my TIME EXPLAINED v2.1 essay. Apologies if you've already read it.

[CraigD]

I understand that if I am standing on earth and you fly away in a speeding spaceship for one year and then back for one year, let's say the equiavalent of 20 years pass on earth.

…

The part that throws me off is that it also states that if throughout your trip you were looking at my watch, then it would seem as if MY watch is the one moving slower.

 

But if that's the case, and you continued to view my watch throughout your entire trip, how could you say that 20 years have gone by for me when you got back, and you not notice it(because it was MY watch that was moving slower)?

An excellent question about Special Relativity, and a fun one to answer.

 

First, let’s describe precisely the imaginary trip of this ship. To keep the calculations simple, let’s have ship accelerated very rapidly for a short time at the beginning of the trip, then moves at a constant velocity directly away from Earth. After a predetermined “turnaround point”, the ship accelerates very rapidly for a short time to a velocity of the same magnitude, opposite direction, directly toward earth. Just before it reaches earth, the ship again accelerates very rapidly in a very short time to a smooth touchdown.

 

Imagine that a distant observer with 0 velocity relative to Earth is watching the trip with an arbitrarily accurate telescope, and, knowing the precise planned course of the ship, the speed of light, and knowledge of simple math and geometry, can compensate for the changing amount of time light from the ship takes to reach him. This observer will see the clock of the accelerated ship always running slower than the clock on Earth.

 

The problem becomes less easy to visualize when we consider what an observer on Earth and on the ship sees of the 2 clocks. The ship will see the clock on the earth moving very slowly during the outward and a part of the inward leg, then suddenly change to move very quickly during the rest of the trip. Earth will see identical slowdowns of the ship’s clock, but the instant at which the rate changes (as a fraction of the total trip time) will be different than the instant that the ship sees the change.

 

A good way to get a “hands on” intuitive feel for this is to write formulas for the 2 clock readings as seen from Earth and from the ship, calculate them for a small collection of times, and write or plot them in a table or a graph. Here’s such a table:

Earth sees                    Ship sees
Earth Clock  Ship clock       Ship Clock  Earth clock
1            .2679491924      .5          .1339745962
2            .5358983848      1           .2679491924
3            .8038475772      1.5         .4019237886
4            1.071796769      2           .5358983848
5            1.339745962      2.5         .6698729810
6            1.607695154      3           .8038475772
7            1.875644347      3.5         .9378221735
8            2.143593539      4           1.071796769
9            2.411542731      4.5         1.205771365
10           2.679491924      5           1.339745962
11           2.947441116      5.5         3.205771365
12           3.215390309      6           5.071796769
13           3.483339501      6.5         6.937822173
14           3.751288694      7           8.803847577
15           4.019237886      7.5         10.66987298
16           4.287187078      8           12.53589838
17           4.555136271      8.5         14.40192378
18           4.823085463      9           16.26794919
19           6.267949192      9.5         18.13397459
20           10               10          20

Note that the units of time used are unimportant. They could be seconds, years, or any other time unit. For the example to resemble a “realistic” “mission to another star”, a large unit such as years is necessary.

 

To make the instants of rate change more clear, I used a 1:2 time dilation factor (ship speed about .866 c). Using the 1:20 time dilation factor, and about 0.99875 c ship speed, the change as seen by the earth occurs so late by its clock that you must use increments of .01 time units to notice it.

 

For those who want to see the formulas involved, here’s the MUMPS code used to generate the table

s V= .75**.5 ;speed is ~ .866
s F=(1-(V**2))**.5 ;time dilation is .5
S K=10 ; turnarround after 10
w "Earth sees",?30,"Ship sees",!,"Earth Clock",?13,"Ship clock",?30,"Ship Clock",?42,"Earth clock",! f T=1:1:K*2 s X1=T*F/(1+V),X2=T-(2*K*V)*F/(1-V),XS1=1-V*T,XS2=T-(2*K-T*V) w T,?13,$e($s(X1>X2:X1,1:X2),1,11),?30,T*F,?42,$e($s(XS1>XS2:XS1,1:XS2),1,11),!

[Uclock]

CraigD

 

An excellent question about Special Relativity, and a fun one to answer.

 

First, let’s describe precisely the imaginary trip of this ship. To keep the calculations simple, let’s have ship accelerated very rapidly for a short time at the beginning of the trip, then moves at a constant velocity directly away from Earth. After a predetermined “turnaround point”, the ship accelerates very rapidly for a short time to a velocity of the same magnitude, opposite direction, directly toward earth. Just before it reaches earth, the ship again accelerates very rapidly in a very short time to a smooth touchdown.

If only we had such a ship!

 

 

Imagine that a distant observer with 0 velocity relative to Earth is watching the trip with an arbitrarily accurate telescope, and, knowing the precise planned course of the ship, the speed of light, and knowledge of simple math and geometry, can compensate for the changing amount of time light from the ship takes to reach him. This observer will see the clock of the accelerated ship always running slower than the clock on Earth.

 

I agree so far.

 

 

The problem becomes less easy to visualize when we consider what an observer on Earth and on the ship sees of the 2 clocks. The ship will see the clock on the earth moving very slowly during the outward and a part of the inward leg, then suddenly change to move very quickly during the rest of the trip.

 

Why?

 

 

Earth will see identical slowdowns of the ship’s clock, but the instant at which the rate changes (as a fraction of the total trip time) will be different than the instant that the ship sees the change.

 

Why would the rates suddenly change? Do you mean this change in the beat of the clocks happens when the ship is accelerating or when it is in uniform motion?

 

 

Tony

[CraigD]

The problem becomes less easy to visualize when we consider what an observer on Earth and on the ship sees of the 2 clocks. The ship will see the clock on the earth moving very slowly during the outward and a part of the inward leg, then suddenly change to move very quickly during the rest of the trip.

Why?

Because the distance traveled by the light with which each clock is “seen” is different for each indicated time of each clock (technically, since the ship goes directly away, then back toward Earth, the light travel distance is the same for each clock at exactly 2 instants, but this qualification makes the previous sentence less understandable, so I’ve only included it in parenthesis).

Why would the rates suddenly change? Do you mean this change in the beat of the clocks happens when the ship is accelerating or when it is in uniform motion?

The sudden change in rate is due to the ships sudden change in direction. It occurs immediately after this change in direction, which in my simplified example, is assumed to occur so quickly that it need no clock-watching occurs during its period of very high acceleration.

 

The data I presented in post #25 comes from 4 equations derived using simple algebra

• X1, the time of the ship’s clock observed by the Earth during the outbound trip
  
• X2, the time of the ship’s clock observed by the Earth during the inbound trip
  
• XS1, the time of the Earth’s clock observed by the ship during the outbound trip
  
• XS2, the time of the Earth’s clock observed by the ship during the inbound trip
  

given

• V, the speed of the ship as observed by Earth
  
• K, the time the ship turns around, known in advance by Earth
  
• T, the elapsed time since the ship began its outbound trip, as measured by the Earth’s clock observed by the Earth
  

The actual formulae are in the second code section in post post #25. Their derivations are not difficult – I’ll post them if anyone wishes.

[Jay-qu]

Jay-qu

 

 

 

And that is supposed to be an explanation?

 

Velocity is relative and the twin paradox still holds.

 

Tony

sorry, the quote doesnt give an explanation, it says that there is one. Craigs post sumises the one I have read. It is all very logical and consistant. When the ship is on the way out and the way back in it has different rates of observed time dilation, even if it is at the same relative speed.

 

Its like doppler shift, on the way out there will be further distance between sucessive pulses when compared to on the way back in.

[HydrogenBond]

Time dilation takes energy to occur. In the case of special relativity, the energy comes from the kinetic energy in velocity. If we were to give off a light signal from a rocket ship traveling near C, moving perpendicualr to a stationary earth reference, the signal would expand as it goes from our zone of distance contraction, into the low distance contraction on the earth reference. The perpendicular motion factors out relative motion to or from us. It would be like light coming out of extreme gravity. It would red shift as space expands as we move away from the gravity zone. In the rocketship's case the energy added to get the motion creates a distance-time contraction shroud around the ship.

 

If you look at EM energy, it is wavelength times frequency. Notice how the blue light compares to the red light; it has a smaller wavelength (distance contracts) and faster frequency (reciprical of frequency is time, with faster frequency meaning longer time or time dilation). With all these photons in the ship time dilated (blue shifted) and energy needed to measure time, time measurement becomes time dilated.

 

For example, say it takes x-energy for our ship clock to tick once. Because the earth sees a red-shifted version of this energy, what the earth sees, is say only half the energy value needed to tick their exact same clock. If this signal was a beacon feeding both clocks so they synchronize, the one on earth would go half as fast due to the red shift, i.e., only enough energy to tick every two seconds. The one on the ship would appear to be going twice as fast. One clock day on the ship would be two clock days on the earth.

 

That explains clocks, but what about matter? If you look at the energy spectrum the fastest frequencies bring about quicker changes but the resultant change, if stable, lasts longer. For example, gamma is associated with extremely rapid nuclear transitions, but creates stable states such as atomic nuclei that can last for billions of years. If you compare this to the low frequency of microwaves, the change of state is slower, like a vibration of a chemical bond, but the stability of the induced state doesn't very last long, i.e., returns toward equilibrium. So the frequency of the energy is connected to the speed of a change, while its reciprical, i.e., time, characterises how long the stable change will sustain. What the blue shift does, within our space ship shroud is to shift toward faster frequency affects that will remain stable for longer periods of time. So we age much slower that way, to go along with the clock.

[CraigD]

Time dilation takes energy to occur. In the case of special relativity, the energy comes from the kinetic energy in velocity.

This is not a prediction of the theory of special relativity. I’m unaware of any experimental data supporting this claim, and aware of much that contradicts it.

 

If time dilation “takes” kinetic energy to occur, the kinetic energy of any body with non-zero velocity would have some of its kinetic energy “taken”, so would have less. Kinetic energy can only be reduced in two ways: by reducing the rest mass of the body, or reducing its velocity. Even for bodies accelerated to very great velocities, such as protons in particle accelerators, neither of these phenomena are observed. If either were, nearly the whole of modern physics would require radical revision.

What the blue shift does, within our space ship shroud is to shift toward faster frequency affects that will remain stable for longer periods of time. So we age much slower that way, to go along with the clock.

This claim violates the theory of relativity’s equivalency principle, which states that the laws of physics are unchanged by an inertial frame’s (also called an “un-accelerated laboratory”) velocity relative to another. A human being in a fast-moving spaceship does not age more slowly because of any change in the frequency of photons he absorbs or emits, nor any increases in the chemical stability of the tissues of his body. His slowed aging relative to a person on Earth, and the difference between a clock on the ship and one on Earth, is due to less time having passed in the ship’s inertial frame.

 

Though it’s tempting to suggest that time dilation is due to phenomena that can be detected within an un-accelerated laboratory, this violates the core principles upon which relativity is built. Relativity is really relative. For example, if we change the spaceflight scenario described in post #25 to that Earth is accelerated, not the ship, less time will pass on the Earth clock than the ship clock. Relativity demands that there are no special frames of reference, or local causes for time dilation.

[jungjedi]

Ok guys I am a bit confused about this whole matter.

 

I understand that if I am standing on earth and you fly away in a speeding spaceship for one year and then back for one year, let's say the equiavalent of 20 years pass on earth.

 

That's great.

 

And then I realize that if I could be looking at your watch it would be moving slower than mine.

 

That's great too.

 

The part that throws me off is that it also states that if throughout your trip you were looking at my watch, then it would seem as if MY watch is the one moving slower.

 

But if that's the case, and you continued to view my watch throughout your entire trip, how could you say that 20 years have gone by for me when you got back, and you not notice it(because it was MY watch that was moving slower)?

 

In other words, from your point of refference only one year went by, and since my watch was moving slower, from your point of refference LESS then one year would have to have gone by for me.....yet when you got back you found that 20 years went by. HOW is this possible?

 

and what if you do a slingshot manuever around the sun?

[CraigD]

and what if you do a slingshot manuever around the sun?

I think you’re thinking of an episode of Star Trek, jung padawan. :) Specifically, the “time-traveling solar slingshot maneuver” from ”Tomorrow Is Yesterday which was repeated in the movie Star Trek IV: The Voyage Home.

 

Though pretty cool special effects for their day, the physics of this is pure fiction. The solar slingshot maneuver is performed more times than astronomers can count, by major and minor solar bodies in cometary orbits. They reach modest velocities of at most a few thousand m/s, (.00001 c), producing insignificant time dilation factors of (around .99999999995 maximum), far from the effect depicted in Star Trek. And, special relativity only allows time travel at an increased rate in the usual direction, into the future, not the past, as in STrek.

[Uclock]

CraigD

 

Because the distance traveled by the light with which each clock is “seen” is different for each indicated time of each clock (technically, since the ship goes directly away, then back toward Earth, the light travel distance is the same for each clock at exactly 2 instants, but this qualification makes the previous sentence less understandable, so I’ve only included it in parenthesis).

 

Sorry, you have completely lost me. The distance light has to travel between the two clocks is exactly the same or are you saying the distance is different?

 

 

Quote:

Why would the rates suddenly change? Do you mean this change in the beat of the clocks happens when the ship is accelerating or when it is in uniform motion?

The sudden change in rate is due to the ships sudden change in direction. It occurs immediately after this change in direction, which in my simplified example, is assumed to occur so quickly that it need no clock-watching occurs during its period of very high acceleration.

 

But a change in direction requires acceleration, so are you saying that the acceleration is causing time to dilate?

 

Tony

[Uclock]

Jay-qu

 

sorry, the quote doesnt give an explanation, it says that there is one. Craigs post sumises the one I have read. It is all very logical and consistant. When the ship is on the way out and the way back in it has different rates of observed time dilation, even if it is at the same relative speed.

 

Its like doppler shift, on the way out there will be further distance between sucessive pulses when compared to on the way back in.

 

I understand doppler shift very well, it is caused by relative velocity but saying time dilates is not the same thing.

 

 

Tony