Further observations about physics – split files

(26) Time travel – we have to incorporate these energy penalties.

We often wonder if it may be possible to return to a past point in time or even a point in the future.

But, let's think of what we know of this "time point".

• First: we usually want to define our destination as a particular time and position on mother Earth. In order to return to that Earth time-point, we would have to materialise at the particular position it occupied at that moment. This gives us a destination point – even though we perceive that earth is no longer there, from our parochial perspective.
• Second: mother Earth never occupies a static position. 2000 year ago, for instance, the Earth was in a very different position around the spiralling Milky Way galaxy. We can work out approximately how far away this is . This is in the region of 40 billion km away. (At its closet approach, Mars is a thousand times closer and it takes a fair bit of resource to reach that.) So, "instantly" transposing to this position would require an enormous amount of energy exchange. Even a seasonal change (winter to summer) involves a long distance.
• We think of gravity as being an attractive force. However, turn this on it's head for a moment and consider that the Earth's surface is being accelerated out at us, like an elevator, at a (constant?) rate of 1G (10 metres/sec/sec). Now, to return to an earlier time we would, effectively, have to fall through the solid surface of the Earth, via it's centre and back in time to a point 200 years earlier. We would need to dissipate 200 years of acceleration at 1 G (an awful lot of seconds in there), ignoring our inability to overcome Pauli's exclusion principle (the reason why banging your head against a brick wall is painful). Note that neutrinos have precious little regard for Pauli's exclusion principle.
• And, we still haven't calculated how the position of the Milky Way galaxy has shifted in that time interval with respect to the centre of mass of the whole universe. This change in position is likely to be far larger than the movement around the Milky Way's spiral arm.
• We can make the same sort of calculation for a trip to visit the future. Effectively, the year 4000 is likely to find Earth in a far different position than it is today. So, the "journey" into the future must include (at least in part) this shift in position.
• And, we have still forgotten to incorporate spatial expansion and contraction. These would also affect the destination "co-ordinates". (If my conjecture is right, spatial expansion – and contraction – are parochial properties; our local galaxy cluster "obeys" contraction but deep intergalactic space – the void stuff – "obeys" expansion.)
• Of course, you could argue that the past could occupy multiple places or that it has no absolute co-ordinates and thus obviate this spatial location restriction. To me that seems absurd. We can calculate how far away the set of co-ordinates of any particular moment in time was (even is perhaps – "is" would be necessary to travel there.).