Relativity: The Physics of Time Dilationindex.htmlshapeimage_1_link_0
 

Uses and Examples of Time Dilation

Whilst we are unable at the moment to achieve speeds sufficient for time dilation to becomes noticeable there are many examples in nature which can. The one which is most often quoted, and was the first experimental proof of time dilation, is the example of muons in the upper atmosphere.


The muon is fundamental particle of the same family as an electron with the same charge but of a larger mass. The muons are created in the upper atmosphere from cosmic ray bombardment and travel down at a high velocity towards the earth’s surface. Unlike the electron though the muon has a very short half life and despite the high velocity very few should reach the surface of the earth.


However when scientists measured the number of muons at the top of a mountain and the number at the bottom at sea level the number which had survived the journey from the top to the bottom of the mountain was much larger than expected. By applying einstein’s theory of special relativity the muons were travelling at a large fraction of the speed of light and so time slowed down for them and, from their point of view, they experienced fewer half lives and thus less decayed than expected when classical mechanics is applied.


When scientists recalculated taking into account time dilation the results matched the observations and thus it was proved that time was slowing down for the muons due to their high velocity relative to us .

Examples of time dilation in nature

  1. Ideas from http://en.wikipedia.org/wiki/Muon#Muon_sources

Uses of time dilation

  1. Textbook “University Physics” not used

In the future when we have developed propulsion systems which can propel space ships at much larger velocities than currently we will be able to use this to allow humans to travel through time. The advantage this will bring is making interplanetary travel possible on human time scales.


Currently it would take hundreds to thousands of years to reach the nearest stars. If and when we achieve much faster space ships it brings these times down to times on a human time scale; however, under classical mechanics, it would still take many a good proportion of a human lifetime to get there and back. Whilst from Earth it would still appear that the astronauts took tens of years for their journey from the astronauts point of view much less time will have passed.


The advantages of this is that the psychological and physiological stresses of long space journeys placed on the astronauts will be significantly reduced. For example a speed of 0.9c will reduce travelling time by just over a half and a speed of 0.95c will reduce the time taken by the astronauts to 3/10 of the time we observe on earth.


N.B. when doing the calculations one can ever look at it from an observer on the Earth point of view where the astronauts appear to have experienced less time than the observer due to time dilation or from the astronauts point of view where length contraction shortens the distance to the planet meaning it simply takes less time to get there, either way the result is the same.

Time Machines

  1. Textbook “University Physics” not used

Whilst time dilation does allow you to travel in time one could therefore build a ‘time machine.” However that machine would only be able to travel forward in time and not backwards in time. If you took a journey into the future you would be unable to return.


Therefore one could go into the future and do the obvious things which spring to a lot of people’s minds such as look at what the lottery results were or who wins the grand national but you would be unable to go back and capitalise on that information. Such a machine would be a double edged sword for people who wanted to try and use information from the future for personal gain.