Is it because the lightcones are not tipped all the way over in which the time axis points downwards?
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possible duplicate of Is time travel possible? Is it possible to go back in time? – Kyle Kanos May 25 '14 at 19:26
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While not an exact duplicate, the answers to the linked question do cover time travel before the invention of such a machine as the Tipler cylinder. – Kyle Kanos May 25 '14 at 19:27
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1@KyleKanos: I'm not sure any of the answers to the proposed duplicate really address the OP's question. – John Rennie May 25 '14 at 19:48
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Prior to the Tipler cylinder being created all the light cones point upwards. So if you attempted to follow time like path taking you backwards in time (that is backwards in the the time coordinate of the observer far from the cylinder) when you reached the time the cylinder was created you'd have to stop. At this point all light cones point upwards so your timelike path would move in the direction of increasing coordinate time again.
John Rennie
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Out of curiosity do you know if R. Mallet's time machine that can only go back to the moment it was turned on an example of a Tipler cone?
I guess I answered my own question. Apparently, it's similar but different. https://en.wikipedia.org/wiki/Ronald_Mallett#Time_travel_research
– dolphus333 May 26 '14 at 00:43 -
If Mallet's idea works it too can only go back to the moment it's turned on. – John Rennie May 26 '14 at 06:06
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What about it? If there's a specific point in that paper you want to pick out why not ask a fresh question about it. – John Rennie May 26 '14 at 06:11
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Where it explains the TARDIS bubble. It says time exists before the bubble meaning can you go back in time before the bubble exist? Even though it is impractical (like other time machine ideas) it's pretty cool. – user122083 May 26 '14 at 15:30