time travel

Telescoping

Wednesday August 10 1960

Robert lit his pipe while William meticulously set the coordinates from the computer printout. “Want to bet?”

William did not look up from fine-tuning the dials and re-checking the flickering oscilloscope screen. “Five dollars that we get something.”

“’Something’ is not going to be enough to make Edward or the General happy. They want the future on film.”

“If we get more delays we can always just step out with a camera. We will be in the future already.”

“Yeah, and fired.”

“I doubt it. This is just a blue-sky project Ed had to try because John and Richard’s hare-brained one-electron idea caught the eye of the General. It will be like the nuclear mothball again. There, done. You can start it.”

Robert put the pipe in the ashtray and walked over to the Contraption controls. He noted down the time and settings in the log, then pressed the button. “Here we go.” The Contraption hummed for a second, the cameras clicked. “OK, you bet we got something. You develop the film.”

 

“We got something!” William was exuberant enough to have forgotten the five dollars. He put down the still moist prints on Robert’s desk. Four black squares. He thrust a magnifying glass into Robert’s hands and pointed at a corner. “Recognize it?”

It took Robert a few seconds to figure out what he was looking at. First he thought there was nothing there but noise, then eight barely visible dots became a familiar shape: Orion. He was seeing a night sky. In a photo taken inside a basement lab. During the day.

“Well… that is really something.”

 

Tuesday August 16 1960

The next attempt was far more meticulous. William had copied the settings from the previous attempt, changed them slightly in the hope of a different angle, and had Raymond re-check it all on the computer despite the cost. This time they developed the film together. As the seal of the United States of America began to develop on the film they both simultaneously turned to each other.

“Am I losing my mind?”

“That would make two of us. Look, there is text there. Some kind of plaque…”

The letters gradually filled in. “THIS PLAQUE COMMEMORATES THE FIRST SUCCESSFUL TRANSCHRONOLOGICAL OBSERVATION August 16 1960 to July 12 2054.” Below was more blurry text.

“Darn, the date is way off…”

“What do you mean? That is today’s date.”

“The other one. Theory said it should be a month in the future.”

“Idiot! We just got a message from the goddamn future! They put a plaque. In space. For us.”

 

Wednesday 14 December 1960

The General was beaming. “Gentlemen, you have done your country a great service. The geographic coordinates on Plaque #2 contained excellent intel. I am not at liberty to say what we found over there in Russia, but this project has already paid off far beyond expectation. You are going to get medals for this.” He paused and added in a lower voice: “I am relieved. I can now go to my grave knowing that the United States is still kicking communist butt 90 years in the future.”

One of the general’s aides later asked Robert: “There is something I do not understand, sir. How did the people in the future know where to put the plaques?”

Robert smiled. “That bothered us too for a while. Then we realized that it was the paperwork that told them. You guys have forced us to document everything. Just saying, it is a huge bother. But that also meant that every setting is written down and archived. Future people with the right clearances can just look up where we looked.”

“And then go into space and place a plaque?”

“Yes. Future America is clearly spacefaring. The most recent plaques also contain coordinate settings for the next one, in addition to the intel.”

He did not mention the mishap. When they entered the coordinates for Plaque #4 given on Plaque #3, William had made a mistake – understandable, since the photo was blurry – and they photographed the wrong spacetime spot. Except that Plaque #4 was there. It took them a while to realize that what mattered was what settings they entered into the archive, not what the plaque said.

“They knew where we would look.” Robert had said with wonder.

“Why did they put in different coordinates on #3 then? We could just set random coordinates and they will put a plaque there.”

“Have a heart. I assume that would force them to run around the entire solar system putting plaques in place. Theory says the given coordinates are roughly in Earth’s vicinity – more convenient for our hard-working future astronauts.”

“You know, we should try putting the wrong settings into the archive.”

“You do that if the next plaque is a dud.”

 

Friday 20 January 1961

Still, something about the pattern bothered Robert. The plaques contained useful information, including how to make a better camera and electronics. The General was delighted, obviously thinking of spy satellites not dependent on film cannisters. But there was not much information about the world: if he had been sending information back to 1866, wouldn’t he have included some modern news clippings, maybe a warning about stopping that Marx guy?

Suppose things did not go well in the future. The successors of that shoe-banging Khrushchev somehow won and instituted their global dictatorship. They would pore over the remaining research of the formerly free world, having their minions squeeze every creative idea out the archives. Including the coordinates for the project. Then they could easily fake messages from a future America to fool his present, maybe even laying the groundwork for their success…

William was surprisingly tricky to convince. Robert had assumed he would be willing to help with the scheme just because it was against the rules, but he had been at least partially taken in by the breath-taking glory of the project and the prospect of his own future career. Still, William was William and could not resist a technical challenge. Setting up an illicit calculation on the computer disguised as an abortive run with a faulty set of punch cards was just his kind of thing. He had always loved cloak-and-dagger stuff. Robert made use of the planned switch to the new cameras to make the disappearance of one roll of film easy to overlook. The security guards knew both of them worked on ungodly hours.

“Want to bet?” William asked.

“Bet what? That we will see a hammer and sickle across the globe?”

“Something simpler: that there will be a plaque saying ‘I see you peeping!’.”

Robert shivered. “No thanks. I just want to be reassured.”

“It is a shame we can’t get better numerical resolution; if we are lucky we will just see Earth. Imagine if we could get enough decimal places to put the viewport above Washington DC.”

The photo was beautiful. Black space, and slightly off-centre there was a blue and white marble. Robert realized that they were the first people ever to see the entire planet from this distance. Maybe in a decade or so, a man on the moon would actually see it like that. But the planet looked fine. Was there maybe glints of something in orbit?

“Glad I did not make the bet with you. No plaque.”

“The operational security of the future leaves a bit to be desired.”

“…that is actually a good answer.”

“What?”

“Imagine you are running Future America, and have a way of telling the past about important things. Like whatever was in Russia, or whatever is in those encrypted sequences on Plaque #9. Great. But Past America can peek at you, and they don’t have all the counterintelligence gadgets and tricks you do. So if they peek at something sensitive – say the future plans for a super H-bomb – then the Past Commies might steal it from you.”

“So the plaques are only giving us what we need, or is safe if there are spies in the project.”

“Future America might even do a mole-hunt this way… But more importantly, you would not want Past America to watch you too freely since that might leak information to not just our adversaries or the adversaries of Future America, but maybe mid-future adversaries too.”

“You are reading too many spy novels.”

“Maybe. But I think we should not try peeking too much. Even if we know we are trustworthy, I have no doubt there are some sticklers in the project – now or in the future – who are paranoid.”

“More paranoid than us? Impossible. But yes.”

With regret Robert burned the photo later that night.

 

February 1962

As the project continued its momentum snowballed and it became ever harder to survey. Manpower was added. Other useful information was sent back – theory, technology, economics, forecasts. All benign. More and more was encrypted. Robert surmised that somebody simply put the encryption keys in the archive and let the future send things back securely to the right recipients.

His own job was increasingly to run the work on building a more efficient “Conduit”. The Contraption would retire in favour of an all-electronic version, all integrated circuits and rapid information flow. It would remove the need for future astronauts to precisely place plaques around the solar system: the future could send information as easily as using ComLogNet teletype terminals.

William was enthusiastically helping the engineers implement the new devices. He seemed almost giddy with energy as new tricks arrived weekly and wonders emerged from the workshop. A better camera? Hah, the new computers were lightyears ahead of anything anybody else had.

So why did Robert feel like he was being fooled?

 

Wednesday 28 February 1962

In a way this was a farewell to the Contraption around which his life had circulated the past few years: tomorrow the Conduit would take over upstairs.

Robert quietly entered the coordinates into the controls. This time he had done most of the work himself: he could run jobs on the new mainframe and the improved algorithms Theory had worked out made a huge difference.

It was also perhaps his last chance to actually do things himself. He had found himself increasingly insulated as a manager – encapsulated by subordinates, regulations, and schedules. The last time he had held a soldering iron was months ago. He relished the muggy red warmth of the darkroom as he developed the photos.

The angles were tilted, but the photos were more unexpected than he had anticipated. One showed what he thought was in the DC region but the whole area was an empty swampland dotted with overgrown ruins. New York was shrouded in a thunderstorm, but he could make out glowing skyscrapers miles high shedding von Kármán vortices in the hurricane strength winds. One photo showed a gigantic structure near the horizon that must have been a hundred kilometres tall, surmounted by an aurora. This was not a communist utopia. Nor was it the United States in any shape or form. It was not a radioactive wasteland – he was pretty sure at least one photo showed some kind of working rail line. This was an alien world.

When William put his hand on his shoulder Robert nearly screamed.

“Anything interesting?”

Wordlessly he showed the photos to William, who nodded. “Thought so.”

“What do you mean?”

“When do you think this project will end?”

Robert gave it some thought. “I assume it will run as long as it is useful.”

“And then what? It is not like we would pack up the Conduit and put it all in archival storage.”

“Of course not. It is tremendously useful.”

“Future America still has the project. They are no doubt getting intel from further down the line. From Future Future America.”

Robert saw it. A telescoping series of Conduits shipping choice information from further into the future to the present. Presents. Some of which would be sending it further back. And at the futuremost end of the series…

“I read a book where they discussed progress, and the author suggested that all of history is speeding up towards some super-future. The Contraption and Conduit allows the super-future to come here.”

“It does not look like there are any people in the super-future.”

“We have been evolving for millions of years, slowly. What if we could just cut to the chase?”

“Humanity ending up like that?” He gestured towards Thunder New York.

“I think that is all computers. Maybe electronic brains are the inhabitants of the future.”

“We must stop it! This is worse than commies. Russians are at least human. We must prevent the Conduit…”

William smiled broadly. “That won’t happen. If you blew up the Conduit, don’t you think there would be a report? A report archived for the future? And if you were Future America, you would probably send back an encrypted message addressed to the right person saying ‘Talk Robert out of doing something stupid tonight’? Even better, a world where someone gets your head screwed on straight, reports accurately about it, and the future sends back a warning to the person is totally consistent.”

Robert stepped away from William in horror. The red gloom of the darkroom made him look monstrous. “You are working for them!”

“Call it freelancing. I get useful tips, I do my part, things turn out as they should. I expect a nice life. But there is more to it than that, Robert. I believe in moral progress. I think those things in your photos probably know better than we do – yes, they are probably more alien than little green men from Mars, but they have literally eons of science, philosophy and whatever comes after that.”

“Mice.”

“Mice?”

“MICE: Money, Ideology, Coercion, Ego. The formula for recruiting intelligence assets. They got you with all but the coercion part.”

“They did not have to. History, or rather physical determinism, coerces us. Or, ‘you can’t fight fate’.”

“I’m doing this to protect free will! Against the Nazis. The commies! Your philosophers!”

“Funny way you are protecting it. You join this organisation, you allow yourself to become a cog in the machine, feel terribly guilty about your little experiments. No, Robert, you are protecting your way of life. You are protecting normality. You could just as well have been in Moscow right now working to protect socialism.”

“Enough! I am going to stop the Conduit!”

William held up a five dollar bill. “Want to bet?”

 

Time travel system

By Stuart Armstrong

Introduction

I’ve been looking to develop a system of time travel in which it’s possible to actually have a proper time war. To make it consistent and interesting, I’ve listed some requirements here. I think I have a fun system that obeys them all.

Time travel/time war requirement:

  • It’s possible to change the past (and the future). These changes don’t just vanish.
  • It’s useful to travel both forwards and backwards in time.
  • You can’t win by just rushing back to the Big Bang, or to the end of the universe.
  • There’s no “orthogonal time” that time travellers follow; I can’t be leaving 2015 to go to 1502 “while” you’re leaving 3015 to arrive at the same place.
  • You can learn about the rules of time travel while doing it; however, time travel must be dangerous to the ignorant (and not just because machines could blow up, or locals could kill you).
  • No restrictions that make no physical sense, or that could be got round by a human or a robot with half a brain. Eg: “you can’t make a second time jump from the arrival point of a first.” However, a robot could build a second copy of a time machine and of itself, and that could then jump back; therefore that initial restriction doesn’t make any particular sense.
  • Similarly, no restrictions that are unphysical or purely narrative.
  • It must be useful to, for instance, leave arrays of computers calculating things for you then jumping to the end to get the answer.
  • Ideally, there would be only one timeline. If there are parallel universes, they must be simply describable, and allow time-travellers to interact with each other in ways they would care about.
  • A variety of different strategies must be possible for fighting the war.

Consistent time travel

Earlier, I listed some requirements for a system of time travel – mainly that it be both scientifically consistent and open to interesting conflicts that aren’t trivially one-sided. Here is my proposal for such a thing, within the general relativity format.

So, suppose you build a time machine, and want to go back in time to kill Hitler, as one does. Your time machine is a 10m diameter sphere, which exchanges place with a similarly-size sphere in 1930. What happens then? The graph here shows the time jump, and the “light-cones” for the departure (blue) and arrival (red) points; under the normal rules of causality, the blue point can only affect things in the grey cone, the red point can only affect things in the black cone.

time_travel01The basic idea is that when you do a time jump like this, then you “fix” your points of departure and arrival. Hence the blue and red points cannot be changed, and the universe rearranges itself to ensure this. The big bang itself is also a fixed point.

All this “fixed point” idea is connected to entropy. Basically, we feel that time advances in one direction rather than the other. Many have argued that this is because entropy (roughly, disorder) increases in one direction, and that this direction points from the past to the future. Since most laws of physics are symmetric in the past and the future, I prefer to think of this as “every law of physics is time-symmetric, but the big bang is a fixed point of low entropy, hence the entropy increase as we go away from it.”

But here I’m introducing two other fixed points. What will that do?

Well, initially, not much. You go back into time, and kill Hitler, and the second world war doesn’t happen (or maybe there’s a big war of most of Europe against the USSR, see configuration 2 in “A Landscape Theory of Aggregation”). Yay! That’s because, close to the red point, causality works pretty much as you’d expect.

However, close to the blue point, things are different.

time_travel02

Here, the universe starts to rearrange things so that the blue point is unchanged. Causality isn’t exactly going backwards, but it is being funnelled in a particular direction. People who descended from others who “should have died” in WW2 start suddenly dying off. Memories shift; records change. By the time you’re very close to the blue point, the world is essentially identical to what it would have been had there been no time travelling.

Does this mean that you time jump made no difference? Not at all. The blue fixed point only constrains what happens in the light cone behind it (hence the red-to-blue rectangle in the picture). Things outside the rectangle are unconstrained – in particular, the future of that rectangle. Now, close to the blue point, the events are “blue” (ie similar to the standard history), so the future of those events are also pretty blue (similar to what would have been without the time jump) – see the blue arrows. At the edge of the rectangle, however, the events are pretty red (the alternative timeline), so the future is also pretty red (ie changed) – see the red arrows. If the influence of the red areas converges back in to the centre, the future will be radically different.

(some people might wonder why there aren’t “changing arrows” extending form the rectangle into the past as well as the future. There might be, but remember we have a fixed point at the big bang, which reduces the impact of these backward changes – and the red point is also fixed, exerting a strong stabilising influence for events in its own backwards light-cone).

So by time travelling, you can change the past, and you can change part of the future – but you can’t change the present.

But what would happen if you stayed alive from 1930, waiting and witnessing history up to the blue point again? This would be very dangerous; to illustrate, let’s change the scale, and assume we’ve only jumped a few minutes into the past.

time_travel03Maybe there you meet your past self, have a conversation about how wise you are, try and have sex with yourself, or whatever time travellers do with past copies of themselves. But this is highly dangerous! Within a few minutes, all trace of future you’s presesence will be gone; you past self will have no memory of it, there will be no physical or mental evidence remaining.

Obviously this is very dangerous for you! The easiest way for there to remain no evidence of you, is for there to be no you. You might say “but what if I do this, or try and do that, or…” But all your plans will fail. You are fighting against causality itself. As you get closer to the blue dot, it’s as if time itself was running backwards, erasing your new timeline, to restore the old one. Cleverness can’t protect you against an inversion of causality.

Your only real chance of survival (unless you do a second time jump to get out of there) is to rush away from the red point at near light-speed, getting yourself to the edge of the rectangle and ejecting yourself from the past of the blue point.

Right, that’s the basic idea!

Multiple time travellers

Ok, the previous section looked at a single time traveller. What happens when there are several? Say two time travellers (blue and green) are both trying to get to the red point (or places close to it). Who gets there “first”?

time_travel04Here is where I define the second important concept for time-travel, that of “priority”. Quite simply, a point with higher priority is fixed relative to the other. For instance, imagine that the blue and green time travellers appear in close proximity to each other:

time_travel06

This is a picture where the green time traveller has a higher priority than the blue one. The green arrival changes the timeline (the green cone) and the blue time traveller fits themselves into this new timeline.

If instead the blue traveller had higher priority, we get the following scenario:

time_travel05

Here the blue traveller arrives in the original (white) timeline, fixing their arrival point. The green time traveller arrives, and generates their own future – but this has to be put back into the first white timeline for the arrival of the blue time traveller.

Being close to a time traveller with a high priority is thus very dangerous! The green time traveller may get erased if they don’t flee-at-almost-light-speed.

Even arriving after a higher-priority time traveller is very dangerous – suppose that the green one has higher priority, and the blue one arrives after. Then suppose the green one realises they’re not exactly at the right place, and jump forwards a bit; then you get:

time_travel07(there’s another reason arriving after a higher priority time traveller is dangerous, as we’ll see).

So how do we determine priority? The simplest seems time-space distance. You start with a priority of zero, and this priority goes down proportional to how far your jump goes.

What about doing a lot of short jumps? You don’t want to allow green to get higher priority by doing a series of jumps:time_travel08This picture suggests how to proceed. Your first jump brings you a priority of -70. Then the second adds a second penalty of -70, bringing the priority penalty to -140 (the yellow point is another time traveller, who will be relevant soon)

How can we formalise this? Well, a second jump is a time jump that would not happen if the first jump hadn’t. So for each arrival in a time jump, you can trace it back to the original jump-point. Then your priority score is the (negative) of the volume of the time-space cone determined by the arrival and original jump-point. Since this volume is the point where your influence is strongest, this makes sense (note for those who study special relativity: using this volume means that you can’t jump “left along a light-beam”, then “right along a light-beam” and arrive with a priority of 0, which you could do if we used distance travelled rather than volume).

Let’s look at that yellow time traveller again. If there was no other time traveller, they would jump from that place. But because of the arrival of the green traveller (at -70), the ripples cause them to leave from a different point in space time, the purple one (the red arrow shows that the arrival there prevents the green time jump, and cause the purple time jump):time_travel09So what happens? Well, the yellow time jump will still happen. It has a priority of 0 (it happened without any influence of any time traveller), so the green arrival at -70 priority can’t change this fixed point. The purple time jump will also happen, but it will happen with a lower priority of -30, since it was caused by time jumps that can ultimately be traced back to the green 0 point. (note: I’m unsure whether there’s any problem with allowing priority to rise as you get back closer to your point of origin; you might prefer to use the smallest cone that includes all jump points that affected you, so the purple point would have priority -70, just like the green point that brought it into existence).

What other differences could there be between the yellow and the purple version? Well, for one, the yellow has no time jumps in their subjective pasts, while the purple has one – the green -70. So as time travellers wiz around, they create (potential) duplicate copies of themselves and other time travellers – but those with the highest priority, and hence the highest power, are those who have no evidence that time jumps work, and do short jumps. As your knowledge of time travel goes up, and as you explore more, your priority sinks, and you become more vulnerable.

So it’s very dangerous even having a conversation with someone of higher priority than yourself! Suppose Mr X talks with Mrs Y, who has higher priority than him. Any decision that Y does subsequently has been affected by that conversation, so her priority sinks to X’s level (call her Y’). But now imagine that, if she wouldn’t have had that conversation, she would have done another time jump anyway. The Y who didn’t have the conversation is not affected by X, so retains her higher priority.

So, imagine that Y would have done another time jump a few minutes after arrival. X arrives and convinces her not to do so (maybe there’s a good reason for that). But the “time jump in an hour” will still happen, because the unaffected Y has higher priority, and X can’t change that. So if the X and Y’ talk or linger too long, they run the risk of getting erased as they get close to the “point where Y would have jumped if X hadn’t been there”. In graphical form, the blue-to-green square is the area in which X and Y’ can operate in, unless they can escape into the white bands:time_travel10So the greatest challenge for a low priority time-traveller is to use their knowledge to evade erasure by higher priority ones. They have a much better understanding of what’s going on, they may know where other time jumps likely end up at or start, they might have experience at “rushing at light speed to get out of cone of danger while preserving most of their personality and memories” (or technology that helps them do so), but they are ever vulnerable. They can kill or influence higher priority time-travellers, but this will only work “until” the point where they would have done a time jump otherwise (and the cone before that point).

So, have I succeeded in creating an interesting time-travel design? Is it broken in any obvious way? Can you imagine interesting stories and conflicts being fought there?