Tuesday, June 19, 2012

Time travel and sleep

Some of the commenters on my last post pointed out that time travel itself is not problematic - after all we travel through it, day by day, all the time.  The problem is the discontinuity.  Can one and the same thing 'jump' from one point in time to some future point in time without existing in the time in between?  If so, then since it does not exist at the point just after which it has jumped, and begins to exist again after it has landed.  This seems to violate Locke's maxim.

Some further points to consider.  Dr Who's time actually isn't discontinuous.  He steps into the Tardis, fiddles about with the dashboard and that glass thing that goes up and down, and waits.  Then he opens the door onto a different time, far in the future perhaps.  From his point of view, there is no discontinuity, which only exists from the point of view of someone outside the Tardis.

It's the same with sleep (by which I mean deep sleep).  My consciousness does not exist during sleep. But there is no apparent discontinuity on my side.  I turn out the light, think of sheep, and then the next thing I know there is light underneath the curtains.  Consciousness in its very nature is continuous, and (as I argued in a series of posts around here) it is finite. 

A further problem.  In what sense am 'I' asleep, or unconscious?  If I am my consciousness, and if my consciousness ceases to exist when I am unconscious, how can I be said to be asleep, or unconscious?



Blogger David Brightly said...

>> Can one and the same thing 'jump' from one point in time to some future point in time without existing in the time in between? If so, then since it does not exist at the point just after which it has jumped, and begins to exist again after it has landed. This seems to violate Locke's maxim. <<

I'm not sure this can be quite right. For it seems to describe the situation of the so-called 'twin paradox'. In the Wikipedia example a spaceship travels to a star 4 light years away and back at speed of 0.8 times the speed of light. Each leg of the journey takes 5 years so if the ship leaves in 2020 it returns in 2030. But because of special relativistic time dilation the clocks on the ship tick at just 0.6 of the rate of the clocks back on Earth and will show the year 2026 on return. So the travellers could be said to 'jump forward' from 2026 to 2030 but they certainly don't pass out of existence for four years and there is no violation of Locke's maxim.

Somewhere in the argument against Locke there is probably an assumption of absolute time.

2:36 p.m.  
Blogger Anthony said...

>> If I am my consciousness...

I would say that is incoherent. It is circular.

9:25 p.m.  
Blogger Anthony said...

David, there's no discontinuity in the travelling twin mind-experiment. If the twins text message their ages back and forth during the trip, their ages would diverge continuously (which is not to say they would diverge linearly - to make the round trip at least one twin would need to accelerate - but given any age difference between 0 and 4 years, there would be a time at which either twin could send the text message such that the other twin would get the message just in time to calculate that age difference).

4:22 a.m.  
Blogger Edward Ockham said...

I agree with Anthony here.

8:36 a.m.  
Blogger David Brightly said...

I'm not sure I understand what you guys mean by a 'discontinuity'. I guess I'm trying to answer the question Ed asks in the final paragraph of Is time travel possible? as to whether Dr Who style forward time travel is inconsistent with Locke. My thought is that Dr Who could spend what is to us more than a hundred years whizzing around at close to the speed of light. But he can make this time interval, for himself, as small as he likes by travelling sufficiently close to light speed. He could leave in our 1999 and return in our 2101 and yet, for him, be away for minutes (if he could withstand the accelerations required). This gives a kind of time travel that doesn't involve any discontinuities (except that he will have to wind his clocks on a bit when he returns in 2101) and does not violate Locke's maxim. There might be other kinds of time travel, maybe involving Parfit/Star Trek style disassembly-reassembly, that would be discontinuous. This, I think, is the more interesting question, more for what it says about our idea of self than for what it says about the possibilities of time travel.

5:27 p.m.  
Blogger Hal said...

Try this: http://tinyurl.com/dy53tj8

6:45 p.m.  

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