# Time dilation can't possibly be explained this easily

1. Nov 24, 2009

### excalion

Before anything, I must admit I am a novice here. I've only casually dabbed in physics here and there throughout college, so I'm far from having a thorough understanding on these matters. I'm posting this hoping for a more educated individual to discredit my own oversimplified insight into time dilation. I hope such a venture is allowed on these forums.

In the past few days I've let my mind drift towards the direction of information relays on the magnitude of galaxies. It is to my understanding that the images we can perceive from stars billions of light years away, are the states of those stars billions of years ago. This delay is caused by the time it would take for light to travel the distance, bringing us the information from those stars. Which led me to consider the possibility that Time Dilation is only an observed phenomenon, in other words, an illusion.

Consider this, suppose there are two points in space. Point A is moving at some fraction of C while point B is stationary. While A travels away from B, the distance between A and B grow greater with each passing moment, and so does the time it would take for light to reach B from A. The only way for B to perceive A, is by perceiving the light traveling from A to B. This would result in a situation where B will begin to see A, as A was X seconds ago, where X(discrepancy) will grow at a linear rate dependent on the fraction of C and with respect to time. Effectively creating a grand illusion for B, that A is traveling through time at a slower rate. While in reality, time has never dilated for neither A nor B, only the latency of information transfer between them has changed.

Which leads me to hesitantly postulate that if A was to turn around at some point in its journey and come back towards B, at this point B will perceive that time has sped up for A. Finally when A has reached B, their timelines will return to perfect sync, to the same as before A's departure.

Now if I recall correctly, one of the reasons why Einstein developed time dilation is to explain why C could be constant for all frames of reference. I don't think I violated that particular rule in my...theory, if you will grant me that. Though I am sure I've violated many other rules, and shown my ignorance on the subject sufficiently. I appreciate any information or insights to show me why the scenario I described is impossible.

2. Nov 24, 2009

### DaveC426913

Time dilation is quite real and can be shown to happen at human-scale.
1] It happens all the time in particle acceletators. In short, at relativistic speeds, particles live longer.
2] GPS technology (such as Tom-Tom) are built upon it being true; they compensate for the dilation. If it were not true, GPS systems would not work.

All you'd need to do to refute your thought experiment is to turn the experiment sideways from your observation ponit so that neither A nor B were farther away. If your hypothesis were true, the time discrepancy would vanish. But it does not.

3. Nov 24, 2009

### JesseM

What you are describing is the Doppler effect, which is present in both classical Newtonian physics and relativity. But in relativity objects moving away from you are visually slowed down by an even greater amount than would be predicted by the classical Doppler effect (see relativistic Doppler shift), and also by a greater amount than would be predicted by the time dilation equation--the visual slowdown in relativity is due to a combination of the two effects. If you subtract off the light travel times, what you're left with is time dilation.

For example, suppose in 2010 you see the image of a clock showing a reading of 4 years, at a distance of 2 light years from you, moving away at 0.6c. Then in 2026 you see an image of the same clock showing a reading of 12 years, at a distance of 8 light years from you. So visually, the clock seemed to take 2026-2010=16 years to tick forward by 12-4=8 years, meaning it appeared to be slowed down by a factor of 0.5 (as would be predicted by the relativistic Doppler equation for v=0.6c). But if you subtract out the light travel times, you conclude that the clock "really" showed a reading of 4 years in 2010-2=2008, and it "really" showed a reading of 12 years in 2026-8=2018, meaning it "really" took 10 years to tick forward by 8 years, so it was "really" running slow by a factor of 0.8 (as would be predicted by the time dilation equation, which says a clock moving at speed v in your frame will be running slow in your frame by $$\sqrt{1 - v^2/c^2}$$).

4. Nov 24, 2009

### A.T.

Unfortunately not:

Last edited by a moderator: May 4, 2017
5. Nov 24, 2009

### excalion

Thank you for your response, but it seems this one is denser than most. =P

The thing I can't understand is this. How did you arrive at 12 years when we look at the clock in 2026? You've said when we first look at the clock, the clock says 4 years at 2008 clock time. Then if we look at it in 2026(2018 clock time), shouldn't it just say 4 + (2018 - 2008) = 14 years? So why 12?

By the way, I worked out the entire thing on paper, and I keep getting 0.65 as the ratio of time distortion. Without using any of the time dilation equations, only my own 'doppler effect' equations I wrote for this particular example. Is 0.65 the right answer? How did you get 0.5 for the doppler equation you used?

6. Nov 24, 2009

### JesseM

In classical mechanics where there is no time dilation, it would be 14 years--if the clock read 4 years in 2008, then 10 years later in 2018 it'd read 14 years. But because of time dilation, the clock only ticks forward by 8 years in 10 years of time in my reference frame, so it only reads 12 years in 2018. Again, the point is that time dilation in relativity is not a consequence of the Doppler effect, it's an entirely separate effect where moving clocks really do run slower in your frame (so if a clock started out synchronized with yours, then moved away at high speed and came back, when you compared it to your clock again after its return you'd find the traveling clock was now behind your own).
If you ignore time dilation and just calculate the apparent visual slowdown in classical physics which is due purely to the Doppler effect, it'd be 0.625, not 0.65. In the example above, if you see the image of the clock reading 4 years in 2010, and you see the image of the clock reading 14 years in 2026, that means it's taken 16 years for you to see the image tick forward by 10 years, and 10/16 = 0.625. The 0.5 I calculated takes into account that the clock is genuinely slowed down by a factor of 0.8 in my frame, so in 2026 I'll only see the image of the clock reading 12 years, not 14.

7. Nov 24, 2009

### excalion

Ah, interesting indeed! Anything to prove this with? Besides a "This is what the top physicists believe, so I'll stick with their formula" response hopefully.

Thanks for the prompt replies and patience btw. Certainly cleared up most of my questions already.

8. Nov 24, 2009

### DaveC426913

Again: the decay rate of certain particles is well-known. If these particles are accelerated to relativistic veloocities their life is dliated exactly in accordance with SR.

It's not simply conjecture. SR is one of the most well-tested theories in science. Every test we have ever done has borne out relativistic time dilation.

9. Nov 24, 2009

### JesseM

Well, you can see lots of experimental evidence for the various predictions of special relativity here, sections 4 and 5 are most directly concerned with time dilation.

10. Nov 25, 2009

### Al68

How about a "This is what physicists were shocked to observe and forced to accept against their will" because it was shoved down their throats by the reality of what they observed?

11. Nov 25, 2009

### mgb_phys

12. Nov 25, 2009

### DaveC426913

That is freakin' awesome.

This guy's entry should be in the PF FAQ under "Is time dilation real?"

13. Nov 25, 2009

### jmallett

I think you are actually quite correct. Einstein never considered actual events. He only considered what an observer observed when the observer was in a different position and time from the event itself.

I, myself, have trouble even agreeing with his most basic assumptions, so how can anything derived from that be correct ?

14. Nov 25, 2009

### DaveC426913

Well, his basic assumptions has been borne out by literally countless experiments, so...

15. Nov 25, 2009

### jmallett

"Well, his basic assumptions has been borne out by literally countless experiments, so... "

I hear this all the time, and have spent quite a bit of time studying those experiments and still find issues. The most classical ones are:

Mitchelson Morley - which only works if a speed of light greater than the speed of light is an a priori assumption

Speeding Train - thought experiment - represents only a very limited special case and can easily be used to show that time and motion are completely irrelevant thus completely eliminating any concerns or worries about relative motion.

Since the "countless experiments" are all based on the assumptions of these considerations then it doesn't matter how many countless experiments are done, does it ?

16. Nov 25, 2009

### mgb_phys

The countless experiments are all the ones done before Einstein which involved moving objects and gave the same result in summer and winter - irrespective of how the earth was moving around the sun/
Then when Maxwell proves that the speed of light is also independant of the observer you need a new theory to explain this

17. Nov 25, 2009

### jmallett

OK, could you give me an example of such an experiment ? I have studied quite a few, and not found one yet that doesn't include the Lorentzian transformation as a way of creating an error that can then has to be explained as a time or space dilation. This includes Einstein's 1905 paper (commonly referred to as OEMB) in which he introduces Special Relativity.

I am certainly interested to study more, but if they involve Lorentz any where along the math then they are easily disproved.

Which experiment, which does not involve the Newtonian basis of the Lorentz transformation, actually "bears out" Special Reality, and by inference time dilation, etc. etc.

18. Nov 26, 2009