∆ The Relativity of Simultaneity.




Relativity talks a lot about 'simultaneity'. But if everything is just here now, then every event is just happening now. In other words perhaps all matter is always, constantly, doing something some where. And nothing is doing anything at a 'different time'.

Even if you or I apparently think about two different things happening at different 'times', (e.g the battle of Hastings and the nasa moon shots), in fact we are just 'thinking', and all the matter in our minds, involved in that thinking is all just here, doing one thing. (I.e we should not confuse thoughts about an event with actual events).

In the picture above ball A is what we might call 'stationary', while ball be is rolling.

The question is, is ball A being stationary 'before' or 'after' ball B is rolling?

or which event, 'being stationary', or 'rolling' is happening, or happened first?

This may seem like a badly worded question, but only because we insist that 'rolling' is a thing that is happening, while 'being stationary' is not.

In discussing simultaneous, relativity often considers that as the speed of light is constant, then if two images of, say two lightening strikes from two different places meet at a point halfway between them, then the the lightening strikes can be said to have occurred simultaneously.  


but even then, the events are said to be simultaneous only to an observer who is stationary relative to the ground the lightening hits.

Relativity suggests that events that are simultaneous to a stationary observer might seem to occur 'one after the other' to a moving observer. Not only this, but also the direction that the observer moves could effectively reverse that order.

this is shown clearly in the 'Elysian  towers' experiment on the excellent 'Relativity - myths and ideas' page by T.L.Hurst.


In this example it is considered that to a stationary observer watching 2 towers being demolished 'simultaneously' the resulting pile of rubble would be symetrical - but a fast traveller moving from left to right might calculate that the west tower collapses - or collapsed before the east tower. the problem here being that the resulting pile of rubble should then be skewed to one side. both observations or calculations cannot turn out to be correct. 




But if matter can just exist, interact move and so on, (but not over time, and not creating a 'temporal record' as it does so, then images etc from 2 events can still be formed and meet at a halfway point between them. This may prove somthing about the events, but it does not prove that 'the past' exists. And proving that the past exists must be fundamental to proving or at least assuming that time exists. because if time exists - but there is no future or no past then what is time meant to be - other than just motion now?

When considering the light from 'simultaneous' lightening strikes things can get overly complicated because lightning, and the light from it are both rather intangible in day to day terms. Instead we can consider the motion of two simple 'footballs' dropping simultaneously in the following setup...


Here two identical balls are allowed to fall on to 2 identical 'ramps'. Using Einstein's definition of simultaneity  - if the balls do move at identical speeds, then if they collide at point M - exactly midway between the two ramps, then it can be said that they did both hit the ground simultaneously.

The point of using this more basic example is to show that Einstein's basic definition of how to work out if two events occurred simultaneously (in the past) does not actually prove that 'the past' exists, or that things move 'over a thing called time'.

Instead it only shows that things can exist, and move. It also does not show that individual objects are ever in 2 different places at different times. That is to say, it is clearer using the idea of say real basket balls, that what ever happens it is clear each ball hits it's ramp once and once only. 

XX note this page to be completed showing how this looks and what it means from another moving frame of reference.
 ( to add - 'stop the world and see how things look').






See the links below for more sections on relativity.


(add links  relativity books, )

Associated links


(xx note - probable factor in the twin towers , the 'apparent' or wrongly assumed error reduces as ships approach)

So although the idea of a difference in simultaneity is integral to the theory, there is no reason to deduce that they actually exist. They could be, and I suggest are, simply a mathematical anomaly produced by the way that Einstein derived the Special Theory.

related to 



 
Relativity Myths - Two Towers
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