Saturday 2 April 2011

Clarification of my Previous Post on Relativity

            I should probably add a bit of clarity to some of the points I made in my previous post on relativity before someone accuses me of not understanding things properly.
            When I stated that 'time and space are relativistic always' I did not refer specifically to the observable time dilations and length contractions. It is still true that relativistic effects are happening around us all the time whenever  non-zero relative velocities are encountered. But the discrepancies do disappear when objects are stationary with respect to each other. However my comment applies equally in this situation  as well if taken in the intended context. We do generally have the experience of objective space and time in that we can’t detect the discrepancies, but my reasoning is slightly more subtle than this. Consider two objects whose relative velocity is gradually reducing to zero. When these objects reach zero velocity with respect to each other they will agree on time durations and distances. In that sense relativistic effects disappear. However if each object's 'reality' prior to this moment was composed of separate versions of space and time then this still remains the case even when their clocks and distances agree in quantative terms. The relativity in this deeper sense does not simply disappear.
            The statement ‘we do live in that world’ can be understood in a similar light. The way relativity works will always prevent us from encountering the potentially paradoxical situations presented by relativity such as the disagreement over sequences of events (the effects of general relativity sort things out in a way to ensure this, as neatly highlighted by the infamous twins paradox). So we don’t 'live in that world' in a directly observable sense but we do in a deeper metaphysical sense. To make this more concrete reflect for a moment on what we would commonly regard as reality. Our reality at any given moment encompasses all events happening in our immediate vicinity that we can readily observe, but also events which we can’t immediately observe. For instance someone in the next door room watching TV is included as part of our reality even though we can’t actually see them.  This means by implication we have to include all events happening in the entire universe at any given moment as part of our reality. We can’t justifiably draw a perimeter around ourselves of some arbitrary diameter and claim anything outside that boundary is not part of our reality (what would you base your choice of distance on?). So we are acknowledging basically that it is the entire list of now events in the universe that comprise our reality at any given moment in time.
               Now suppose there is an alien in some distant galaxy many light years from Earth who is watching TV at this very moment in their living room. I won’t bother to do the necessary calculations to produce specific numbers but providing we are prepared to consider distances of sufficient magnitude the effects of relativity will be magnified to produce more dramatic discrepancies in time and space for much slower relative velocities between objects. If we ignore things such as gravitational effects, expansion of the universe and the motion of the planets we can imagine that there is no relative motion between you and this alien at this moment in time whilst he is sitting watching TV. Consequently his conception of now, the entire list of now events in the entire universe which comprise his conception of reality, coincides with yours. If this alien  now walks across his living room to switch his TV set off, and the direction of his walk happens to be in a direction away from Earth, then his list of now events will include events in Earth time (from our perspective) that happened hundreds, thousand or millions of years ago, depending on exactly what distance we are considering.
          Just a few moments ago before he got up to switch his TV set off both realities coincided. Now there is  suddenly this huge discrepancy.  And the important thing to bear in mind here is that his conception of reality is just as valid as yours. This is one of the key aspects of special relativity - it's symmetry.
          Now suppose instead the alien had chosen to walk in a direction towards Earth rather than away from it. This will consequently have similar results but  this time going forward into Earth's future.  If the distance between planets is made sufficiently large enough the Earth  won't even exist  in his reality now!  During this short interval of time (from the alien's perspective) our sun went supernovae and engulfed the entire Earth!
            The fact that relativity works in a way to always prevent us from directly witnessing the bizarre behaviour of time dilation, length contraction and lack of simultaneity cuts little ice doesn’t it ? At least on  purely metaphysical grounds. It’s almost as if the universe is pretending that  space and time exist but  at the same time will always contrive to conceal this fact from us  (I guess Einstein screwed that one up). What a sneaky universe!
            Quantum mechanics presents us with even more startling results. The delayed quantum eraser experiment demonstrates retrocausality in such a striking way so as to establish beyond doubt that when ‘reality’ and knowledge are entangled the question of ‘when’ something happened quickly becomes quite meaningless. The notion of an objective reality being out there all the time simply doesn’t hold water. Again the universe invests considerable cunning in trying to disguise it's bizarre quantum behavour at the macro level of reality. The universe likes to pretend things are real when they are not. Even more sneakiness from the universe!

Still believe time is real?

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