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Comment by threeseed | Hacker News Reader

I've never understood this logic. If say time travel is invented in year 3000. Then surely by 3050 it would be affordable for a certain segment of society. And be 3070 available for a mass market. And by 3100 available in watch form.

So shouldn't we expect there to be millions/billions of people interfering with the past. A significant percentage of which would be deliberately aiming to manipulate, destroy, communicate, affect and do all the things we expect people wouldn't.

Clearly it means either two things. 1: time travel is not possible. 2: going back in time forks the universe/space-time (About Time is a recent movie that proposes this).

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Almost, but I'd like to suggest an amendment to your first conclusion:

Time travel may well be possible, but unbounded backwards time travel is clearly not possible.

It may be the case that a machine will be invented that allows people to travel back only as far as when the machine was first switched on.

Similarly, a technique may be invented by which you may be able to temporarily travel infinitely into the future, and be snapped back to your present.

It may be the case that backwards time travel consumes so much of some finite resource that few or no future time travellers could possibly make it into our past.

Garry Kilworth's story "On the Watchtower at Plataea" involves a group of time travelers, from the story's "present", who push back earlier and earlier into the past... until they can't go any further because another group is coming the other way, from the past (due to the technology involved, each prevents the other from going further in their desired direction).

The "present" group then end up, essentially, in a standoff, watching the other group from a vantage point near an ancient Greek battlefield, and pointing out that they must eventually "lose" because both groups are now essentially in normal time. Which is moving from the past to the "present" from which they left.

It's been 60 years since nuclear power was invented, so in 10 years it'll be available for mass market? I'd also like my watch form plane.

What if it's so energy intensive that a future dyson sphere can only power it once a year. It doesn't matter how cheap the machine is, if the resources are expensive.

That poses the question whether a civilization that is advanced enough to build a dyson sphere would be able to build a second one somewhere else. The species would have enough time to collect energy and improve the machine until no reachable sun would be usable. And though we don't carry nuclear reactors in our watches (I guess smartphone would be more reasonable these days) we might carry fusion reactors in the year 38000.

Indeed energy conservashion and entropy equalizashion was a large problem.

Interventions in the past are possible as long as they don't change the future in significant ways. Think of it as Schrödinger's cat who is not dead as long as you don't look inside the box.

Or we are the future as it's happening so its up to us to figure it out.

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