xkcd #2976: Time Traveler Causes of Death
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Many a hungry time traveler has Googled 'trilobites shellfish allergy' only to find their carrier had no coverage in the Ordovician.
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A time machine is a teleportation machine. If we can imagine a time machine existing, a teleportation machine isn't really far fetched.
I cannot wait for time travel to exist so all the pedants online can be like “um actually, it’s a space-time machine”
Edit: because I am also pedantic like this.
A time machine is a faster than light drive.
Well, the other way 'round, really, but same difference.
And to come back you need a slower than (but very close to) light drive.
well, if you rewind time and stay in the box, the box would probably stay on earth, but I have no idea how time travel would work.
There is no cosmic frame of reference. Earth is moving, the sun is moving, the galaxy is moving, but you can choose any frame of reference within that. It'd be really silly to use the suns frame of reference, you'd use Earth's.
There is no cosmic frame of reference
There is. Just because we can't correctly find and use it with our knowledge doesn't mean there isn't.
it'd be really silly
What would be silly is thinking that earth is some magical center of the universe.... We have abandoned this concept about 500 years ago.
It isn't about how humans view their place in the cosmos.
It's about relativity.
Space and time are inseparable. Hence the term space-time. You can thank Einstein for that.
The comment you replied to states It's also about frames of reference, probably one of the most crucial aspects of relaticity.
Einstein has proven that time and space appear and are experienced differently for each and every observer. With the effects being significantly different depending on gravity, speed and distances.
If you could reverse time travel then the space would conform to the time you travelled to.
If you could reverse time travel then the space would conform to the time you travelled to.
Really? What else would conform to the past point in time? Would fabric in my clothes disintegrate and transforms to something else? Would I, because I, well, didn't exist in that past? Then it wouldn't really be time travel, would it?
Or would the clothes stay, because they are mine and important for me and would I stay on earth, because that's my baseline? Is universe somehow "me-centric"? Not really likely, is it?
You need to abandon your idea of time travel as seeking in a video with rewind button.
According to our current understanding of physics time travel is impossible, but we are talking about a word where it is clearly possible, so you can't really constraint yourself with the limits as we know them now.
I don't exist in the future, yet, here I am, in the future, with all my clothes in tact.
There is nothing in physics that actually says it's impossible.
Maybe your current understanding of physics says it's impossible.
Nothing about it is about me.
IT'S ABOUT FRAMES OF FUCKING REFERENCE. Inertial frames of reference, relativistic frames of reference, etc.
(This is relativity, if you think it's about me, you obviously need to learn little more.)
*Also, I've blocked this user.
I don't think that's a particularly useful thing to do when discussing physics, throwing a temper tantrum because someone has a more casual understanding than yours.
*Also, I've blocked this user.
Oh no, have you used the word relativity too many times and now you have no more arguments? :D
If we can’t find the cosmic frame of reference, then how do we know it even exists? Sure, you can assume it exists, and call that a hypothesis. If only someone had a way to test that hypothesis.
Since a time machine has to fiddle with space-time somehow and that is an attribute of the universe – i agree, the universe is the frame of reference.
The earth is not a magical center of the universe, it's just convenient right now to use it as a frame of reference no need to associate it to magical thinking.
I hear the universe is infinite, and no matter how far away from earth you go, there's just infinitely more universe. So like if you are standing on earth looking twelve billion light years that way and then twelve billion light years the other way you are in a sphere of unimaginable size right? But if you actually went twelve billion light years that way once you get there you can still look this way or that way and see twelve billion more light years every which way. So from that perspective, pretty much anywhere in the universe is the center of the universe...from a certain point of view...
The universe seems pretty infinite when viewed with our current tools and from our perspective. I would still argue that we can’t really be sure just yet. However, we can say it’s effectively infinite just like a lot of things in physics are effectively massless, effectively frictionless etc. You totally can make your calculations work really well even though your model cuts some corners here and there.
In many cases, you can even assume the Earth is flat and simple maths still works well enough. However, when you zoom out and start doing more complex calculations, you run into trouble and need to upgrade to a more sophisticated model. I would argue that the current assumption of the universe being infinite can fall into the same category.
We disproved a cosmic frame of reference, or "ether" hypothesis using interferometry. It is well worth a read, I think you will enjoy it.
Not exactly - what was proven is that there's no way to distinguish between inertial frames of reference. There could be a universal frame of reference, which would most likely be the average velocity of all things in the universe. There's not much point in making a distinction in most cases, because if you can't detect it, it might as well not exist - but since we're making up time travel, we might as well make up a universal frame of reference, it doesn't break anything time travel hasn't already broken...
[off topic]
One of my favorite time travel novels is 'The Big Time' by Fritz Leiber.
The two big ideas in the book. First, that there's a Law of Conservation of Reality. Go back in time and shoot Hitler. He dies. Then gets better, really fast. Twenty minutes after you shoot him, he's fine. Spend your whole life shooting him and the history books will just ignore it. It takes an army of time travelers working night and day to get any changes to stick.
Second idea. There are two armies, both trying to change the past/future. They have been at it since before the Big Bang and will go on until the Heat Death of the Universe. They recruit humans but no human has ever seen the big bosses, just low ranking stooges.
The first one was also used in the short series "11.22.63". Going back to change things results in huge amounts of temporal inertia to overcome.
And the second one reminds of the TV series "Travelers", with future factions of time travelers emerging from the changes of previous time travelers in the past. It's worth noticing that time travelers from "Travelers" only displaces their mind consciousnesses, not their entire bodies.
He dies.
That's an unusual take on it. That would definitely have been recorded somewhere as a miraculous recovery. Usually it's written that the time travelling assassin fails in such a way that no-one notices, and if they do have some kind of effect, generally ends up being the cause of the history they were taught rather than the changer of it.
The author did a few stories based on the 'Change War.'
In one, a time traveler goes back and takes the bullets out of a gun, hoping to prevent a death. There's no gunshot, but the victim is hit by a meteor and dies anyway. The idea is that Time is immutable and almost impossible to change with only one set of hands.
. It takes an army of time travelers working night and day to get any changes to stick.
Changes do occur in the story. The participants talk about the 'Change Winds' and how people can just disappear because thier timeline has been shifted and their parents never met.
Ctrl+F Hitler, ah, there it is. I feel like the xkcd comic missed an opportunity to have a 1932-1945 segment in there about the biggest cause of death for time travelers being OTHER time travelers killing them before they can successfully go back in time and kill Hitler, lol.
Re: conservation of reality, I feel like if I went back and shot Hitler, I would miss, or be stopped by security, or bad weather, or my gun would misfire, or even if I managed to actually do it, he'd be replaced by a look alike, and then it would turn out the guy we always thought was Hitler was actually just an actor, or something. Like if someone went back and killed baby Adolph when he was six months old, the parents would adopt another kid and name IT adolph, and there you go. Whatever happened happened and can't be undone, not through magic resuscitation of a corpse, but through smooth and natural intervention of reality itself, if that makes sense..