# Again with a time machine question **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [October 20, 2002, 7:55pm UTC](https://boards.straightdope.com/t/again-with-a-time-machine-question/133126 "2002-10-20T19:55:01Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Mr.Blue\_Sky](https://avatars.discourse-cdn.com/v4/letter/m/d26b3c/32.png) [@Mr.Blue\_Sky](https://boards.straightdope.com/u/Mr.Blue_Sky)\ **Post date:** [October 20, 2002, 7:55pm UTC](https://boards.straightdope.com/t/again-with-a-time-machine-question/133126/1 "2002-10-20T19:55:01Z")
IIRC, Hawking stated that time travel was impossible otherwise we’d be inundated with time travelers from the future and even if a time machine COULD be built, you couldn’t travel back to a time BEFORE the machine was built. So here’s the question: If the above is true and you couldn’t travel back before the machine was built, how would you know if the machine actually works? Let’s say I build a time machine and _theoretically_ it should work. Let’s also say I complete the machine at noon on Monday. I plan on hopping into it at 1pm and travelling back to 12:30pm. When 12:30pm rolls around, I DON’T appear from the future to let myself know the machine works. So when 1pm rolls around, do I get in the machine or not? ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [October 20, 2002, 10:03pm UTC](https://boards.straightdope.com/t/again-with-a-time-machine-question/133126/2 "2002-10-20T22:03:04Z")
Of course you get in. If you don’t, there’s no way you could appear at 12:30. Let me amend that. Put in a hamster, with a radio beacon. What if there is a _spatial_ rather than temporal problem. What if the test subject appears a hundred miles above, or below!? I guess your machine is designed to move you back in time, and reconstitute you within the same chamber? Even if it works, what will you do with the extra you? Good luck! ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [October 21, 2002, 2:41am UTC](https://boards.straightdope.com/t/again-with-a-time-machine-question/133126/3 "2002-10-21T02:41:24Z")
Dammit, when I invent one, I’m going to travel back and give the plans to myself. ---
**Author:** ![happyheathen](https://avatars.discourse-cdn.com/v4/letter/h/b5e925/32.png) [@happyheathen](https://boards.straightdope.com/u/happyheathen)\ **Post date:** [October 21, 2002, 3:32am UTC](https://boards.straightdope.com/t/again-with-a-time-machine-question/133126/4 "2002-10-21T03:32:47Z")
or, you could wait 24 hours to test it, go back 24 hours and see if yesterdays news is on again. duh? ---
**Author:** ![Skeezix](https://avatars.discourse-cdn.com/v4/letter/s/839c29/32.png) [@Skeezix](https://boards.straightdope.com/u/Skeezix)\ **Post date:** [October 21, 2002, 6:50am UTC](https://boards.straightdope.com/t/again-with-a-time-machine-question/133126/5 "2002-10-21T06:50:40Z")
> [@](#): > > _Originally posted by **Mr. Blue Sky** _: > **If the above is true and you couldn’t travel back before the machine was built, how would you know if the machine actually works?** The Scene: A basement workshop, in an anonymous suburban home. Anywhere, USA. It is some undetermined hour in the middle of the night. Let’s say 2ish. _Norman Commal works feverishly at a cluttered workbench, beside which is a large piece of machinery, hidden under a tarp. It emits an occasional electronic noise, and the odd flash of light, visible through the covering._ Norman: That should do it… yeah, a little more solder _there_, and… {Voice from OS}: Norm? You coming to bed, or not? It’s like… let’s say 2ish. You’ve got a class to teach in the morning, you know. Norman: Yes dear, I’ve just got a couple little things to finish up. I’ll be up in a bit. _Norman retouches the bit of electronics in his hand, looking back and forth from the part to the covered machine, making minute adjustments. This goes on for quite a while._ {Voice from OS}: Norm, come to bed! You’re going to sleep right through your first two classes at this rate! Norman: Yes dear. _Norman lifts the edge of the tarp, and snaps the last bit of circuitboard into place. The machine makes a small humming noise, and a few extra lights come on, highlighting the shape of the device through the tarp._ Norman: There, that should do… _Suddenly, in a burst of cheap special effects smoke, a machine looking much like the one under the tarp is lowered down on mostly invisible wires from above stage. When it touches down (and when Norman recovers from his coughing fit) a door opens on the front of the machine. Out steps a woman dressed in a fuzzy red robe, her hair tied back with a black kerchief._ Woman: Dammit, Norman, I told you to come to bed three hours ago, and I meant it! Norman: Yes dear. _Exuent all_ [sub]I’m thinking something along these lines, anyway.[/sub] ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [October 21, 2002, 12:44pm UTC](https://boards.straightdope.com/t/again-with-a-time-machine-question/133126/6 "2002-10-21T12:44:14Z")
Long before that, IIRC, Larry Niven wrote that a timeline with a Time Machine was inherently unstable,m because if one could exist, someone would go back and change the past. On the other hand, I have to note that noted physicist _and_ science-fiction author Robert L. Forward has stated that he won’t believe Time Travel is impossible until and unless someone gives him a plausible _scientific_ proof. None of this kill-you-own-grandfather stuff. He’s written his own time travel novel, **Time Master**.