Done Deal

1.

"You have about half an inch of sugar in that coffee, now", the Executive remarked, "it's like a sediment layer on the bottom."

Unable to be bothered to answer, I stirred and poured down half the glass, which was now basically overly sweet warm milk with a hint of coffee far away. We met, as usual, at a coffee shop approximately halfway between our homes. It's our neutral ground in a friendly passive-aggressive power struggle regarding who should have to walk the furthest to the meeting. That much was as usual. What was unusual was that the Executive was on time for our meeting. A rare event indeed, and as the sugar made its way into my blood I wonder if I should have interpreted all the times I had waited as a second front in our power struggle. But that would have to wait. I wanted to know what was so important as to cause the Executive's perpetual Hawaiian-time to go atomic.

"So, what was the deal you spoke about?", I asked.

"Well... ok, this is what it boils down to: it's about programming a time machine."

"What, like a movie prop?"

"No. A real one."

"Why do you need a programmer for that? Can't the people building the machine send the plans for it back in time to themselves, or something."

"That's what they did. A month ago the device was dug out of solid granite during construction of a tunnel in the London Underground. It was found in a spherical void in the rock about a meter across. There's no way it could have been put there. It had been in that rock for about a year, and was sent from a point in time about a week from now. The Ministry of Defense grabbed it and as you know, I have some contacts there, so when they needed to contact you, they went through me."

"Needed to contact me?"

"It's your code that runs the machine. Your name is all over it. It's signed with your key. Not your current. The one that is from tomorrow - so the comments say anyway."

"So it's fate that I should do this job, then?"

"Looks like it."

"Well, I guess this will not be a very stressful project, then. I mean, success is guaranteed. But what if I refuse, or just go to sleep for a week?"

"I asked the same questions. The explanation I got is that you won't."

"So, if I were to refuse the job via email then there would be an undetectable transmission error of some kind and the email would magically come across as accepting it?"

"No, history isn't made of extremely rare events. Everything will appear to be normal. You will accept the job from curiosity, or for some other perfectly common and normal reason that is indistinguishable from free will."

"But it won't actually be free will, then."

"I asked that, too. They said it will be as free a will as you've ever really had."

"So all the passages in the holy books about everything happening, not according to our will, but to God's will, were true. Funny that a deterministic universe would end up containing an accurate description of itself."

"It also contains a ton of self-help books, so I'd say the universe is hedging its bets."

"You know, I can still refuse and walk out. I can still say no."

"Yes, in theory you can. But will you? That's what matters in the end."

"What? No. I'm in. I just got to see this."

"Good, because I've already signed the papers - for you, too."

2.

The next day I dutifully generated a private / public key pair and sent it over. I got a short reply saying that yes, this is indeed the key that was used to sign the code that controlled the machine. A key, created from over a thousand random digits, that hadn't existed until today had been used to sign code that was at least a month old. There could only be two explanations: One, that by random chance the generator had created the exact thousand-digit sequence that was required to match the signing key; and this had, again by random chance, been done on the exact millisecond that the comments in the time machine code predicted - a prediction that I had not been told about and so could not be influenced by. Two, that the device really was a time machine.

We were on.

3.

The windowless conference room was sterile, quiet, and I suspected it was also underground. I had lost track of vertical movement as we went there. It was just I and the Executive there. I brought up a clean sheet of paper, drew a couple of ellipses to get the ballpoint pen going, and signalled that I was ready for business.

"All right. What's the deal? How do we do this?"

"I've been talking with the MoD people. This is what they know they want: First, a briefing about how the device works. This is expected in two days. Then, in five days, the sending of the device back in time a year so it can be found. The rest we're still trying to figure out."

"I'm expected to figure out how the device works?"

"They think it's in the software. The hardware has been examined, X-rayed, probed, and scanned to eternity and back, and while they understand the components, it's a mystery how the thing can travel in time."

"And the software, no clues there? Nothing an AI can figure out?"

"AIs have not been trained on working time machine software. They've given up and are leaving it to the original author to figure out their own code."

"Well, you know what they say about writing really smart code - you have to be twice as smart to figure it out when you come back to it."

"Yeah. Well, they said that it looked like it was written by a moron with Tourette's," the Executive chuckled.

4.

The next 48 hours were proof that certain success doesn't imply ease. The strangest thing about the device was how much off-the-shelf it was. It consisted of a plastic box, connected to two peripherals by means of, what I could see, standard USB cabling. It had a standard RJ45 network socket. It ran Linux. Files had creation and modification dates in the near future, and the system clock was as expected a month ahead. I immediately saw the truth in the description of the code given by the MoD people: not only was it a job done in haste, it had some quite colorful names in it that made me slightly ashamed of alternate-me, as I've made a point of not trying to be "funny" when writing code or comments.

The process was quite a straightforward one, however. I fired up the coding assistant, picked some part of the code that looked central and started figuring things out from there. It looked like nothing I had ever written in terms of architecture or framework, but slowly I began to get a model of how it worked, and the overview graphs went from a heap of spaghetti to something that could be comprehended.

Two days were not enough to reverse-engineer everything, or even the most, but I was quite sure that I had the organization of the major parts covered. Above all, I had been able to figure out the general idea of time travel as implemented by this device, and enough that I believed I would be able to send it back in time.

5.

I think it was the same conference room. It looked the same, but I hadn't been able to form any kind of map of this facility, and maybe it was reconfigured all the time, so maybe it was a different one. I started the projector and brought up a photo of the device.

"Before I get into the operation of the device, I have to explain the idea of 'block time'", I started, wondering how many of the five people besides the Executive that were listening that I had lost already. "Imagine the world as a movie where one frame follows the other. Now stack these frames so you have a solid block. Yes sir, we're doing this old school, not digital. Each object will now trace out a path in this block of stacked celluloid sheets, called a 'world line'. Each such world line must of course obey the laws of nature, so there are limits to what world lines are possible. Now, time travel has been thought of as something similar to travel in a car - you hop into your time machine and drive through time until you get where you want to be. The result, for travel into the past, is a world line that curves back on itself, or that somehow leaves the block altogether and does the travel in some kind of secondary time. This way of time travel gets full of paradoxes quickly.

"What the device actually does is more like quantum teleportation. It alters the world lines of things in the past, with the result that the present immediately changes into what would have happened if the alteration had taken place. As far as I can tell, no object actually travels through time. Actually, the best way of describing it would be to say that the device can change the present into what it would have been if the past had been manipulated in a certain way."

"So how does it do this?", one of the MoDs interrupted.

"I don't know. What I know is this. The system consists of several layers, as usual. Top level is a standard web interface that provides for controls. Then, there's the high-level operations layer. It has only one function - send something from now into the past - and it also communicates with this part", I pointed to a component that looked like a hockey puck with a short antenna sticking up from it, "which is called the datum. It is the point of reference for any operation. Any send operation is measured from the tip of the 'antenna', and any time offset is measured in the reference frame of the datum. This high-level layer then does all the coordinate transformations and decomposes the send command into a sequence of operations that are sent to a lower-level library that in turn does the actual job of..."

I felt something click in my head. What I had just said felt wrong. This was not how it worked at all. Never mind for now. I continued, "...doing. I'm still trying to figure out what happens, because I don't know just where the low level layer is. It's not in any of the source code that I have access to."

"Will you be able to do the send in three days?", the same MoD asked. Thank God for goal-focused people.

"Yes. The log files of the device show that it was successfully sent back this Thursday at half past three. It was the first activation of the device. The first one in the logs at least."

6.

"You know it can't send anything into the future", I said to the Executive when there were just the two of us in the room again, "there is a square root calculation in the time offset that expects a real valued result - and future times are negative."

I could see the mental gears start to grind.

"The device is based on there only being a 'now'", I went on, "with a future that is determined but not real, and a past that only exists in the sense that we can observe the results of past events. For us to find the device - being sent here from the future - you'd need a bunch of alternate-us living a year ahead of us in time, sending things back just like you'd throw things off the back of a truck going down the street of time with another truck following behind on the same street. But the device is based on the assumption that such a thing doesn't exist! Either the assumption is completely wrong, in which case the device can't work, or it is a simplification of reality - good enough to work, but not one hundred percent accurate."

7.

Thursday came. At exactly 15:32:19.455 I activated the device with the "send_self" program. The time and space offsets were hard-coded into the program, and the origin from which those were measured was of course hard-coded into reality itself, it being predetermined exactly what would happen. I made no special effort to trigger the program just at the predetermined moment in time. Overall, there is no more sense of events being predetermined than there had ever been in my life. Yet, the time is of course correct down to the millisecond, which was the resolution of the timestamp.

From my point of view, nothing happens. The program terminates successfully with no output and no error. At first the Executive is worried, but I explain that this is expected. The activation would only ensure that the events that had taken place would take place, and that we would end up just like this.

But I still have to figure out just how the device worked, and quite frankly I don't even know how far away I am from that. The work so far had only touched on the higher levels of the stack. I knew about the conceptual framework of time travel, but I have no idea how it was actually done as I haven't been able to find the program code that interfaced with the time travel hardware.

It is time to pick apart the only working instance of a time travel program. I had thought I would find the source code for it, but now I'm convinced to try something else. I set the coding assistant to decompile, load up the "send_self" program in a debugger, and start to browse through it. It turns out that the Executive had been right in worrying: The program does nothing except output a log entry of the current time and exit.

8.

"How are things coming along?" the Executive asks.

It feels so good when I close my eyes. My mouth feels dry, my body tired, and every article of clothing manages to feel uncomfortable. I can barely see the screen. My eyes don't focus, and when they do, the colors feel washed out.

It has been over 36 hours since I last slept. MoD wants answers. I am exhausted, and not making much progress.

"I'm trying to wrap my head around what has been going on, trying to figure out what parts of the program code are what they claim to be, what are lies and what are... something else."

"Look, is there a chance that this whole time travel thing is just one big hoax?" the Executive asks.

"The public / private key incident is proof against that. It's just too improbable. This device contained information from the future."

"But what if the key wasn't random?"

"If the key was pre-generated and then just dropped on my workstation by someone, making it seem like it was generated, you mean?"

"Yes, exactly."

"They wouldn't have been able to fake the generation time. I chose that, and it matched to the millisecond. Even if the fake key program had the time hard-coded, I would have noticed that the claimed generation time was off. Same thing goes for Thursday's activation, or whatever you'd call it. Even if they control the code that outputs the timestamps, they can only fake the milliseconds. If the program outputs the wrong hour or minute, we'll notice. Then there's the issue of how the device was found."

"Maybe that's just one big lie. I wasn't there in the tunnel. You weren't. MoD wasn't there."

"Some tunnel worker just keeps the device in his pocket, and then goes 'look what I found'?"

"Yes."

"Sounds like a lot of work for very little. Why go through all that? And it still doesn't explain the timestamps."

"Maybe to get a device close to the MoD network?"

"Given the scrutiny that this device has been under, I don't think that's the way to go. It basically has 'please examine me thoroughly' written on it in block letters. USB stick in the parking lot is better."

"Well, either way, that's what they think. The MoDs."

"Based on what?"

"Based on this thing being off-the-shelf hardware and therefore not capable of sending stuff through time. We have no proof of it actually working."

I have no good answer to that.

The Executive goes on, "they're canceling the project."

I'm too tired to argue. Something doesn't feel right, because the timestamps aren't explained, but if the MoD essentially says that the task is impossible I'm not going to waste any more effort on it. Time to get out of here.

I take one last look at the screen. It is covered in lines representing time. The lines curve, branch and join as I had tried to figure out just how the device had come into existence, and thus how the very first time travel had worked.

9.

That's how I remember it happening. I was not allowed to record or take notes. But now I have written it down and can sleep. I'll make sense of it later. You have read all I know.

10.

After two days straight just sleeping and eating, I come up with a way to explain what I had observed.

The device worked by causing the effects of a past event - the "send" - to appear in the present. What if you send a nuke with a timer back to before you were born and blow up grandpa? You'd destroy yourself. The present would instantly change to the what would have happened if gramps took a bucket of sunshine in the head, with everyone having their memories updated accordingly to make everything consistent. You, however, would be caught in this cascade of cause and effect and cease to exist. There is no paradox, as the device can be thought of as rearranging the present - just in a very sophisticated way. Nothing actually moved into the past, as the past doesn't exist except as traces in the present.

You just had to be sure that you weren't in the blast radius, the part of reality that would end up rearranged. If you were, you'd be hoist by your own petard.

Which alternate-me, past-me, had been.

The problem with the device appearing from the future were many, but the most important one was that it assumed that there is a future me, a year ahead in time, that can send stuff back to present me, and the maker of the device explicitly stated that such a thing doesn't exist. The future has no objective existence.

There was only one way to explain what had happened, and that is that the activation of the device last Thursday had happened. But it wasn't present-me that did it. It was past me.

That activation was what annihilated past me, rewrote my memories - rewrote me - and the memories of everyone else, and made the present appear as if a device had been sent back in time a year to be discovered by a tunnel worker a month ago. It probably did a lot more, since everything pointed to this being an uncontrolled failure. Who knows how far back history had been rewritten, and how far out into the universe the effect was felt? Instead of building a time machine and rid us of Hitler, maybe past me had created him. Their motivations and goals are no more.

The resulting cause and effect cascade had wiped out the part of reality that contained the actual time-travel parts, but some traces of the way reality was up until last Thursday had remained - thus the key pair and the timestamps. Maybe the forces close to the datum had interfered with themselves to create this jagged edge between the old universe and the new, while the alteration farther away had been smoother.

It is even possible that it rearranged the universe so that time travel was made impossible, and thus a working time machine could not be allowed to exist any more. The new iteration of reality would have to exclude the missing low-level code and its accompanying hardware. Talk about pulling the ladder up.

11.

"But we sat here, having coffee, prior to that!" the Executive protests.

"How do you know?"

"I remember it!"

"Yes, but what we have here is a perfect memory-rewriting machine. You know, it's said that we can't prove that God created us, with all our memories, thirty seconds ago. I think I have a pretty good case for that device having created the present world last Thursday."

"So my past, then, my memories, aren't real?"

I stop a moment to think about that one before answering. "They're as real as they've ever really been," I offer.