Adam Samberg asks Neil Degrasse Tyson three questions

This is the entire basis for the greatest time travel romp ever written, Robert Silverberg’s Up The Line, wherein the main character chances into a career as a “Time Courier”, taking wealthy tourists into the heart of key historical moments, watching the throngs mount each time, and taking care not to interact with the other “versions” of himself and his colleagues in attendance.

(When I’m a bigtime Hollywood producer, this book is SO getting filmed.)

There’s also a “Time Patrol” corps which retroactively fixes any paradoxes caused by reckless tourists or errant couriers. I see no risk or problem with this system :slight_smile:

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Yeah, I’m aware of that common caveat, but to me it always seemed like an arbitrary cop out to easily dismiss the “tourist” problem as I’ve never heard any reason couched in physics as to why this governance would enforce itself.

Similar to one of my fav sci-fi movies “The Grand Tour” where a small hotelier hosts some strange guests. After a bit of digging he finds their odd passports with dates that coincide with some of the biggest disasters in history (Hindenburg, San Fran fire, etc) and he realizes something horrible is about to happen to his little town and they are time tourists stopping off to witness it. It sort of started the thread in my head decades ago about how big the crowds would actually be though.
And the “multiple versions” of himself points to my issue with duplicating matter in the finite universe (although others above may have a solution based on multiple dimensions in the time/space continuum.

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Heheh. I knew someone would have a way around my postulation… which is what makes talking about this stuff so fun. :wink:


If you think about it, we are already “traveling” forward in time. Changing velocity, which we are constantly doing on a minuscule basis, simply changes the rate of our time travel. No mass or energy gets added and no duplicates get created.

Traveling backward seems to be where things get hairy.

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The only problem with time travel is that you could run into your mom as a teenager and she could fall in love with you.


Well, a Tipler cylinder would theoretically work by warping spacetime so severely that your light-cone “tips over”, so what seems to you to be normal progression through time is, to the rest of the universe, a journey into the past. But this warping only occurs while the cylinder exists and is operational. So, no journeys beyond its creation.

Or if you somehow create a wormhole and send one end of it scooting round the galaxy near the speed of light, then when you bring it back it will have aged considerably less, thanks to relativistic time dilation. E.g., in 2016 you create a wormhole and send one end off on its journey with a clock embedded in it. Ten years later, it returns home: your watch says it’s 2026, but the wormhole clock says it’s 2017. If you now enter the wormhole via the end you sent off round the universe, you will, so the theory goes, come out the other end in 2017: you’ll have travelled nine years into the past. But again, you can’t go back any further than 2016, because before then there wasn’t any wormhole to come out of.

So no, it’s not really an arbitrary cop-out.

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What happened? He was rudely interrupted by James Corden at the 43 second mark (NdGT: “So, second…” JC: “So you don’t. Wait. Sss-No. Wa-wait…”).

As consolation, here’s a video of Neil deGrasse Tyson during a lecture at the University of Washington, answering the question “Do you think it will ever be possible for a human to travel in time?” (you should turn closed captions on)

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