Disclaimer: I do not own Back to the Future.

Author's Note: All right, this chapter is a complicated one given that it tries to explain a theory which was very vague in my head when I wrote it down. If anyone needs any more explanation feel free to ask me, but I think Doc and Chris are explaining it as well as I could possibly do it myself. Finally, there's a bit of a retcon in this chapter, which I'll tell you upfront as not to cause any more confusion; Chris mentions Calvin went to October 21st, 2015 after leaving 1958 the first time in "I Didn't Invent Any Time Machine". That's not true to the story, but it's something I needed to change to make the time travel mechanics fit - if Calvin had returned to 1985 without time getting the chance to go past October 2015, there would have been no means for Doc and Marty to return home and be around for Calvin to meet them. Or at least, that's how I imagine time travel works in my head when there's several time machines involved. I'm probably making it sound more complicated than it is now. Anyway, I didn't rewrite that part of IDIATM because I couldn't work out how to fit it in, but that's how it happened now. And well, that's it for my confusing-sounding Author's Note. Please read and review!

Chapter Three

Sunday, December 22, 1985
07:30 PM PST
Hill Valley, California

Looking up at the equipment in front of him, Calvin McFly swallowed nervously. They had all been gathered in Doc's house – he, Marty, their parents, Jennifer and Ann and their parents, Mike, Claudia, Susan, and of course Doc and Chris themselves. When they had come in, he had immediately been guided into the living room, where Calvin had once more noticed the strange sleep-inducer lookalike device, which now appeared to be completed. Marty had asked him what it was, and he had replied that he hadn't got any idea. And now, roughly twenty minutes after he had arrived, he still hadn't.

With everyone now present, sitting on their chairs and waiting anxiously, Calvin finally dared to ask the question which was on everybody's minds. "Are you going to explain all this to us, now?" he questioned Chris, who was pacing up and down the room, alternating between checking some calculations, making sure the computers were doing their job, and fetching their guests coffee.

"In a minute" the inventor promised, stopping to look at Calvin. "I understand that you're eager to know what this is all about, and we're not planning to have you all wait much longer, but Emmett needs to fetch the chalkboard. We've decided to use it in order to explain to you just exactly what the problem we're dealing with is."

"A chalkboard, Chris?" Susan repeated, chuckling. "Why didn't you use the computer?"

"Because the main explanations could just as well be done on ordinary chalkboards, and likely would be more comprehensible, even" her husband replied. "And we didn't want to install the necessary equipment for a computer viewing that everyone would be able to see – it might not have taken more than an hour, but it's unnecessary, so…" He shrugged. "If it ends up not working out, we'll use the computers."

At that moment, Doc entered, hauling with him a large chalkboard. Chris rushed over to help him, and they set it up at the front of the room. They then turned to the crowd, which had mostly silenced at the unexpected sight. It therefore didn't take Doc much effort to ensure that everybody was quiet as they began the demonstration.

"As you're all well aware," the inventor began, "a week ago we discovered that Calvin was fading from existence. Ordinarily such a process would commence perhaps a few days at most after the event occurs that sets history on such a path that his existence would become impossible. Then – although admittedly we haven't witnessed that process yet, not in its entirety – it would occur relatively quickly, as seen with Marty in 1955. What is happening to Calvin is therefore a mystery to us, as not only didn't it commence a full month and a half after he came to live in this world, it is also going extremely slowly and irregularly. Calvin, you are fine right now, aren't you?"

"Uh, yeah" the teen responded. "I had a stomach ache this morning, but it was gone soon after. The last time I really had another erasure attack was yesterday afternoon."

Chris nodded, taking over from his counterpart. "Furthermore, my wife and family are also from another reality, like Calvin is" he continued. "Therefore, if anything would be affecting Calvin's existence, then logically it would also be affecting ours. Admittedly, we are from a different reality than Calvin is, and one which resembles this world much less – but logically, that shouldn't have to make any difference. We therefore had a conundrum on our hands, and after various testing and theorizing, we finally decided to ask you to come over tonight because we think we might have a valid theory for why all of this is happening – although it's not a nice one."

Calvin took a deep breath. "Explain" he said.

"I will – although I'm warning you, this will require a lot of fourth- and even fifth-dimensional thinking" Doc replied, walking up to the chalkboard and drawing a line on it. At the left he set '1955', somewhat more to the right he put '1958' and at the right end he wrote '1985'. "Imagine that this line represents time" he started. "I am here showing the original timeline in the period from 1955 to 1985. For the purpose of this evening, we will call it timeline A, although there has been some habit to call the alternate timeline Chris and his family are from by that name but that is irrelevant right now. This is the timeline in which George and Lorraine were unhappily married, and the mall was named Twin Pines." He shot an apologetic look at Calvin's parents, who were blushing. "Marty and I met in 1975 in that timeline, and ten years later I was shot at the mall while performing my first time travel experiment. Marty jumped back in time thirty years, creating timeline B." The inventor drew a line in the form of a half-circle with its ends at 1955 and 1985, and drew a short diagonal line off the 1955 part before creating a straight line just right of it. "Now you will remember," he continued, "that this Marty is the one prior to time travel and is therefore Marty and Calvin. They are the same – it is just one Marty McFly."

"Check, Doc" Marty replied. The others nodded in agreement.

Doc nodded at them. "During the week Marty spent in 1955" – he took a piece of red chalk and accentuated the first part of timeline B – "he managed to get his parents to fall in love and went back to the future. This is where their paths separate. Marty ended up going back to 1985" – another half-circle to the end of the line – "and went with me to the future. There, Biff Tannen got his hands on the time machine." The inventor drew another half circle, this one starting in the space above 1985, and ending in-between 1955 and 1958. "We still don't know when Biff went back to in the 1950s to give himself the almanac, but what we do know is that it occurred after Marty's visit to 1955 or at least after his arrival, because Calvin did exist in that November week." The inventor drew a new diagonal line from the point Biff arrived, and a second adjacent line where he added 'C' at the end after 1985. "Therefore, despite the radically different world Biff created, in which Michael ended up growing up and becoming that timeline's version of Marty, there was still a version of Marty" – the scientist tapped on the red part of the line – "who was in 1955, even in the past of timeline C, because Biff couldn't have changed it without going to a time before then. And that Marty also ended up going forwards" – another half-line – "and because that was the new timeline, timeline C, he ended up in the 1985 of timeline C. That Marty was our Calvin." He turned to his crowd. "Still with me so far?"

"It's very confusing, but I think I get it" George McFly replied. His wife nodded, as did Robert and Marlene Parker. "Although perhaps you could use more colors of chalk, just to ensure it's clear. But go on – I'd like to know how much relevancy this has to Calvin's actual situation right now."

"I'm getting there" Doc replied. "Now, as you know, Calvin ended up spending two months in the alternate 1985 of timeline C, along with Mike. The reason he didn't get erased from existence then is unclear, but presumably it was because that timeline was headed towards a paradox anyway, and thus Calvin wouldn't necessarily have to disappear – but never mind that right now. The point is that Calvin ended up visiting 2010 with all of the A-family, and eventually wound up going back in time from 1985 to 1958, creating timeline D." Another half circle and diagonal line with accompanying horizontal line was drawn, this one starting in 1958. "This timeline is a near duplicate of timeline B, with only the years between Biff getting the almanac and losing it to Calvin being different."

"Within this timeline," Chris then added, taking over, "Calvin jumped to the evening of October 21st 2015, which was shown in the almanac as the date he should look for the locals. However, he couldn't find them, and headed back to 1985. Due to his visit to 2015, the timeline had for the first time gone on to the point where Old Biff returned the DeLorean, and so Emmett and his group had left shortly before Calvin did. Therefore, when Calvin headed back to 1985, he found Emmett and Marty there. This is timeline E – although in reality timeline F, due to the fact that Emmett and Marty would have created another timeline themselves while going back, with Calvin being undisturbed by the reality change and creating a wholly new timeline himself by going back to 1985." He grinned, noticing the perplexed looks on the faces of their visitors. "Now are you still with us?"

"Not really, but carry on" Jennifer muttered. "So, we're now in timeline E? Or F?"

"For convenience's sake, we'll call it timeline F and add a ripple down from 1985-D to it" Doc replied, doing so on the chalkboard. However, now I'd like you all to pay attention, because here it really starts to get confusing as it will now involve multiple dimensions."

"Dimensions?" Calvin questioned.

"Indeed" Doc confirmed. "Calvin, you didn't start erasing in 1985-F because you were there too short for the ripple effect to catch up to you – you had come through several different timelines and eras thus far, after all, and only were there for a few hours. However, judging from the information we've acquired now, you went through a much more complex situation afterwards, and that is the reason you're now reacting so slowly." When the teen continued to give him a baffled look, the inventor proceeded. "As you remember, you, Marty and I decided to connect the time machines to each other that night, in order for the transition process to go smoother."

"That's right" Calvin agreed. "Are you saying that that would have done something to the time travel process?"

"Exactly" the inventor said. "The process of linking the two time machines went fairly far, allowing the one in the main car to control the Destination Time of the other car, and combining the outputs of the flux capacitor – in fact, assembling both flux capacitors together. Thus, the Fusion and plutonium reactors were combined, creating an overload of 2.42 gigawatts." He sighed awkwardly. "As you might recall, I mentioned that one of the reasons for creating such a complex construction was to avoid creating two timelines at once by going back at the same time, which might cause us to punch a hole in the space-time continuum so big that we could be sucked into another parallel dimension. Well, it turns out that I was wrong. The construction we built didn't avoid the problem, but worsened it instead. We ended up creating a new, duplicate dimension when we went back in time."

"Creating a new dimension?" Marty said skeptically. "Is that even possible?"

"Apparently, it is" Mike answered before Doc or Chris could say anything. "I don't understand it either, but all the tests we have done points to the theory that every time we or you travelled back or forwards in the combined time machines, a new dimension was created, with an identical past until the moment you came in. That was why we never noticed anything off – the new dimension was simply created from the moment you came in, and you didn't see any more changes than you expected to see."

"Then what's the difference between a normal timeline and a dimension like that?" Lorraine asked.

"There isn't really one" Doc admitted. "Except for the fact that unlike timelines, dimensions simply continue their existence once you leave it, so the original dimension we came from still existed alongside with the one we were unwittingly creating. Due to that, there wasn't any issue with people erasing either, since people from one dimension can and will co-exist with the locals of another – and that's exactly why Chris and his family haven't ended up with those problems." He turned to Chris. "Would you like to explain the next part?"

"Certainly" the other inventor agreed. He drew a new line somewhat lower on the board, and labeled it 'Dim. 1', once again putting '1958' and '1985' at the ends. "This is the original dimension," he unnecessarily stated. "When going back in time and universes, the dual time machine created dimension 2" – he drew a diagonal line from the right end to the left end of another parallel line from it – "which was the place in which Calvin returned the almanac to Biff. However, due to the connection between the time machines, when you travelled to 1985, another universe must have been created" – he drew one more diagonal and horizontal line – "dimension 3, which they ended up in on New Years' Eve of that year, and which must have been exactly the same as dimension 2 up until the point that they arrived. This is the dimension my family and I are from. With Marty's extensive help, we were freed from Biff, and travelled back to 1958 – another parallel line and diagonal line to accompany it – creating dimension 4. There, we took the almanac from Biff once more, and after that we disconnected the two time vehicles. There we come to our confusing element."

Doc nodded. "Robert, Marlene, I've asked your daughter to come over twice this last week, haven't I?" Jennifer and Ann's parents nodded. "When I did that, we still hadn't entirely developed this theory, and wanted to see if there was anything in Jennifer's DNA similar or dissimilar to ours, since she stayed in her home dimension the whole time. The result was, surprisingly, a match. Where as there was a slight discrepancy in the DNA of my counterpart and his family that we pinpointed as being due to them originating from a different dimension, Jennifer's DNA didn't seem to be any different from that of me, or my Marty, or Calvin. Therefore, the obvious conclusion is that Jennifer is also from dimension 1, and thus, that we somehow managed to return to it from dimension 4. This is dimension 1, which explains exactly why Calvin is the only one feeling ill – he is the only one who is both a duplicate of our Marty and from this dimension."

Their guests were baffled. "But why would you end up back in this world?" Robert Parker asked. "Even if the cars were disconnected again, wouldn't it just work like normal time travel – which I suppose is an oxymoron – and leave you in the 1985 of dimension 4? And even if it didn't for you, why didn't it happen for the other version of you either?"

"That's exactly what we've been trying to resolve" Chris replied. "Most likely, Emmett and Marty ended up back in this dimension because, freed from the compulsion to hop through various universes at once, his time machine returned to its home – which was, of course, this world. We're not sure yet why we ended up going along. The most likely argument until now is that we left some equipment in place while dismantling the connection in 1958 – admittedly, we were in a hurry – and that was just enough to maintain a link between our two cars strong enough to at least synch up the dimensional part of the destination, and send us to the world my counterpart was from – even though we left 1958 over half a minute after my other self and Marty did."

"Right…" Marty replied. "Well, Doc, Chris, I can't say that this isn't interesting, and it sounds plausible. But what exactly does this have to do with Calvin's slow fading process, and more importantly – how does it give us a clue for doing something about it?"

"We were just getting to that" Doc said. "From the research we have done through the past weeks, it appears that the dimensional jump has drastically decelerated Calvin's fading process. I just described to you all the journeys Calvin made even before he left this dimension – it would probably have taken the ripple effect a few days to catch up with him even if he had just stayed home in 1985 after getting back to the 'good' future. However, he also visited other dimensions, three of them even, and that appears to have distorted the process much more. The ripple effect has thus become much slower, something we are now able to measure because of this." He pointed at the gadget Calvin had noticed earlier. "This is the Ripple Effect Indicator, or REI. Chris and I built it together, and judging from it, starting on October 27th, the effect has been catching up to Calvin at roughly 3 years each day – in which years hopped in another dimension could be down to only one year per day, while years hopped through in our dimension, although going significantly slower than in a normal erasure process, could be up to 4 years per day."

Marty frowned. "But didn't the effect work much slower that week I was trapped in '55?" he asked. "You told me that one week after pushing Dad out of the way of Grandpa's car, the ripple effect had reached 1968 or at least my conception in 1967, so wouldn't that have been slightly less than 2 years per day?"

"That's true," Chris acknowledged, "but you're forgetting one thing. In 1955 you were erasing so slowly because of the future being in a relative state of flux and you still being capable of pushing it back into a direction so that you would exist, as you eventually did – a chance that ended up becoming less likely as the week passed. However, if something radically changes in the past that makes something virtually impossible – like with the newspapers changing – the change would be almost instantaneous. This process is more like something in-between; Calvin still exists in this world, but as you, as Marty McFly, and therefore he is not fading as fast as he would have if there hadn't been any Marty at all, or when he hadn't had any dimension hops in-between, but not as slow as he would if he were still well before the fatal point in 1968 and the Marty McFly that would be born could still become him. Get it?"

"I suppose" Marty muttered, confused.

Calvin then piped up. "So, does the fact that you built that Ripple Effect Indicator mean you can tell me when I'll end up erased from existence?"

Doc and Chris shared awkward looks. "It does" the former admitted. "If nothing changes between now and then – and that's a big if, considering the fact that we're planning to do everything we can to help you – the ripple effect would likely fully catch up to you a few days after the New Years, erasing you from the time stream. The symptoms you've been displaying now will likely get worse in the meantime, although it might not seem so to you as you grow more accustomed to them."

As Calvin bent his head down in desperation and depression, a murmur grew throughout the crowd. Lorraine was horrified; George was as well, but seemed more resigned, as if he had already been anticipating something like this. The others seemed to be in a state of shock, with the exception of Ann, who was casting her eyes down and blinking in a manner that made it obvious she didn't want anyone to see she was near tears. Only Mike looked relatively normal, mostly because he'd seen much of it coming. He absent-mindedly patted his sister on her shoulder, but his mind seemed to be elsewhere, and finally he turned to the two scientists who were still standing uncomfortably at front. "Dad?" he asked.

"Yes, Mike?" Chris replied.

"I think I've got an idea to – well, not solve, but at least postpone this mess."

The inventor shared glances with his counterpart, then shrugged. "Let's hear it, son" he said, friendly.

Mike did. "So, basically," he began, "all the time travelling Calvin has done is slowing down his erasure process, right?"

"That's what we've concluded from everything that we have researched, yes" Doc replied. "Do you mean…"

He did. "So why don't we just take Cal back and forwards as far as possible? You can travel in a time period covering ten thousand years with that thing, remember, so if we took the DeLorean back to zero AD – well, technically I suppose it would be one AD – and then forwards to 9999 AD, we might get up to twelve thousand days added to his lifetime – that's forty years, Dad, Doc. Even if the calculations you made were wrong, it should at least be enough to last him quite a while. And in the meantime, you can work on a more permanent solution to the problem."

"Hey, yeah, that's right, Doc" Marty chimed in. "You could take Calvin back as far as you want – perhaps even beyond zero, if you'd install some sort of B.C. readout." He frowned. "You know, I've always wondered why you never did that in the first place. You are limiting your destinations with the system you have now, aren't you?"

"That's right" the inventor admitted. "But travelling back before the start of our calendar could bring me into areas of theological-geologist disputes, and while I suppose it might be interesting to get the answer to those questions, I believe there are some things that should remain a mystery and a matter of faith. There are so many controversies and questions you could solve with the time machine – indeed, that is one of the reasons I've built it – and you can't go on forever with it. Besides, even if one could go back millions of years and there would be a dinosaur-populated world with no humans there, the risk of changing history is too great. You know how much can be changed in just thirty years. Today is one more piece of evidence for that. So, limiting backwards time travel is reasonable enough. Furthermore, travelling to the future, I'm of a mind to stick close to home as well. Take weaponry, for one thing. Just hundred years ago, people were fighting on horses and with primitive guns. Right now, we have devastating nuclear weapons that can be used to destroy countries. Take that to its natural conclusion, and by 2100 every man might be able to build a device that could destroy humanity. Worldwide change in technology and culture has been accelerating exponentially over the last years, and I've stuck close to home thus far because I'm very uncertain about what I might find if I went too far."

Chris nodded. "My counterpart is right" he agreed. "That's part of the reasons why I kept my time machine and travels within the same limits – and, of course, the need to follow my original counterpart's system. But Mike has got a point. If well prepared, we could launch an expedition into the far past, making a brief hop to the start of our calendar before returning home. Only staying there for a few minutes could do wonders for Calvin's condition."

The boy in question began to smile. "That might work" he agreed. "But we should be very careful, shouldn't we? Even if we're just going to hang out over Hill Valley in that time period for a while, we might want to research if there are any Indians around that might see us."

"Exactly" Doc confirmed. "That might cause significant changes to history, something we need to avoid at all cost lest we worsen the situation. Unfortunately, I don't think records are available that are so detailed and precise that they explain the location of every tribe in the area around that time. Even in the future, I don't think we'd be able to find that information. We'd just have to hope that we don't run into anything or anyone – and take precautions for if we do."

"Is that really necessary?" Ann wondered. "Wouldn't you just have to stay for only a few minutes, as you just said, in order for Calvin's situation to be improved?"

"Theoretically, yes" Chris agreed. "But we don't know much about his condition yet – what we've just told you is in fact all theorizing, with very few facts to go on. The best option would be to hang around for a while and do a few tests before going back home. The better we know what's wrong and how it all works, the better we know how to fix it – and that's something I intend to do, permanently, no matter how long we could postpone Calvin's erasure due to journeys in time."

"And what would that permanent solution look like?" Susan wondered. "Taking Calvin to another dimension again?" She suddenly shivered. "Chris, you're not planning to leave him there, are you?"

Her husband shook his head reassuringly. "Not if there is any other option" he told her. "And only if Calvin would agree to it. I suppose that, presuming we could find a way to travel between dimensions, it would be the safest plan, but I wouldn't like it. My counterpart and I want to find a way for Calvin to survive that involves him staying in this dimension, and I'm sure Calvin agrees with that a hundred percent." The teen vigorously nodded his consent. "And besides, it might not even be possible to open a gate to another dimension and return safely. Despite all we've told you, I'm thinking that when we all returned to this dimension, it might have been more luck than something made inevitable due to the time vehicle's new control system."

"Yeah, this whole dimension travel thing does sound like a tricky business" Calvin agreed. "And… you know, I suppose that if we'd open another hole through dimensions the same way we did before, we could create a duplicate of this dimension, right?" Chris nodded. "But well, I wouldn't want to leave you behind – and besides, if we're doing that, wouldn't those others be doing the same with their Calvin?"

"Now there's an interesting question" Chris speculated. "I would think that, if we just hopped ahead a minute while simultaneously shifting into another dimension, we'd end up in a world where Calvin also left but just didn't return… but would that mean we'd be depriving them of their Calvin?" The inventor frowned. "Hmm. We'd have to think about that some more. One more reason to keep this all within the realm of theories for now rather than basing any concrete action on it – besides Mike's plan, of course, which couldn't cause any harm nevertheless."

"Yes, I think we can do that without any worries" Doc agreed. "But of course, that will have to be planned thoroughly as well. I don't think we'll need any native clothes this time, as the whole point of the expedition is to avoid being seen by locals, but just in case, we might want to bring some tools to help repair parts of the time machine, if they are damaged."

"I'd hate to think of that happening" Calvin said, wincing. "The thought of being trapped in another era – again – is bad enough, but having it be a primitive time period like 0 AD would totally suck."

"I can't help but agree with you" Chris nodded. "We'll have to take strong precautions for everything, but fortunately you don't have school to go to tomorrow or any other upcoming day due to the holidays, so we'll be able to go as early as possible, without having to worry about the need to follow classes while either preparing, or the day after our departure and subsequent return. Of course, logically, we should be able to come back just the moment after we left, but as you know, our journeys rarely go off without a glitch."

Calvin nodded. "So, when are we going to leave? Tomorrow?"

"Tomorrow it should be" Doc confirmed. "There are a lot of things we need to prepare and you can't just leave right now, not if we want everything to be done right. But I'm sure we can make everything ready for us to leave tomorrow evening. If you put your mind to it, after all, you can accomplish anything."

oooooooo

The next day was filled with frantic preparation of all that might be needed on the short journey to the past. Doc made sure to refill the gas tank, while Chris collected the tools they would need if anything went wrong, and Mike headed off to the town library. After several hours of extended research, he reported back home that he had found everything about Hill Valley roughly two thousand years ago which there was to find, and that it was virtually nothing. There were some small tribes in the area around that time, but Mike reported that it would be highly unlikely for them to run into those groups.

Meanwhile, Calvin had another difficult task to accomplish – convincing his mother and father to let him go. While they understood that the trip was going to be short, they were still reluctant to agree to something which could potentially strand their youngest son in a time so far from his own that the entire country didn't even exist yet (which, admittedly, considering the United States' relatively short history, was not much of a feat). When Calvin pointed out that Doc and Chris had taken numerous short trips to the future on which nothing had happened, and indeed that Chris had even taken two during his own honeymoon, they became a little more willing to let him go, although especially Lorraine still gave him such a firm hug just before he went off to the Brown house that Calvin thought he would choke.

Next up was the question of who would actually be going back in time. That Calvin was going there could be no doubt – after all, he was the one whose health was in danger. That either Doc or Chris or both would be coming along to fly the car was a given as well, and when they both decided to go there was no objection. However, Mike, his sense of curiosity piquing up at the thought of seeing the area Hill Valley would one day be in so long ago – even if, as he admitted himself, there wouldn't be all that much to see except fields and some hills – wanted to go along, as did Ann, who almost seemed to get emotional at the thought. Doc and Chris, however, thought this was absurd, considering the fact that it was just a brief trip and that cramming five people into a two-seater car for no good reason was unthinkable. Thus, Mike and Ann were forced to stay in Doc's lab, where they would wait for the others to return.

After drilling Calvin on the tiniest details of his impending trip – and freaking out when the poor kid once more complained about feeling faint and the equipment to monitor erasure was already being rushed in before Calvin declared everything was all right again – Doc and Chris headed with him to the DeLorean that would be used that night. They had resolved to use Doc's DeLorean, for no real reason except that Calvin was one of his versions of Marty, and after refilling the Fusion reactor they got inside. After Doc rattled off his newly-introduced password for entry to the time circuits, they turned on and Calvin could see the readouts.

Destination Time
DEC 20 1985 01:00 AM

Present Time
DEC 23 1985 10:53 PM

Last Time Departed
DEC 19 2025 07:54 PM

"Where to?" he asked. "Just January 1st of the year zero?"

"There is no year zero" Doc pointed out. "Admittedly, I did talk about going back to a date within that year during the time machine's first test, but that was mostly intended to show you exactly how the time machine worked and to give you an impression of what one could do with it rather than an actual analysis. Christ probably wasn't born on December 25th, either. I suppose typing in zero might just end us in the year 1 B.C. – which might not be a bad idea, considering that we want to give you as much time as possible to shield your internal functions from the ripple effect." He raised his voice. "Destination Time: January 1st, 0, 6:00 AM."

His counterpart frowned. "Are you sure you want to risk this, Emmett?" he asked with some skepticism. "You don't know if the car will be able to complete the transit. Wouldn't it be safer to just go to 1 AD instead? It's only a year of difference, after all."

"Perhaps you're right," Doc admitted, "but I did install the 0 AD option into the time circuits when I first built the DeLorean, and it did register the date as possible. Judging how the time vehicle works and the time circuitry's internal components, logic dictates that the car should just take us to 1 BC."

"Maybe" Chris agreed. "You might be right, but it still sounds very risky to me. Do you really want to do that? I understand that it would be interesting to find out what happens if you go back that far – as a matter of fact, I've spent some time wondering about it – but there are risks involved, and we did have some bad luck the previous times we attempted to go back on what should have been an easy journey. Isn't that exactly why we spent so much effort on preparing this?"

"It is" Doc said. "Still, as you said, it would be very interesting to find out if the time vehicle would complete the transit – even though, admittedly, there wouldn't be a way to check unless we were to fly over to Europe and convert Roman dates to ours, taking into account other date changes that might have happened in-between. But it is much safer than, say, going forwards to December 31st of 9999 and wait for midnight to occur. In that case, the time circuits would have to describe a date it cannot describe, namely the year 10.000 – which would cause system failure. This is a safer possibility to satisfy our curiosities."

As he saw Chris raising his voice to object to that, Calvin spoke up. "I don't want to cause you to fight, Doc, Chris" he said. "Let's just leave now, okay? It's 10:57 already, and you did promise that we'd be back by eleven. Mike and Ann are going to be either angry or worried if we're not."

The two inventors exchanged glances. "Fine" Chris finally muttered, resigned. "But if something goes wrong, you can fix it on your own." His features softened. "Now that's just a joke – but I won't make you forget this if it goes wrong, Emmett Lathrop Brown."

"I wouldn't expect anything else, Christopher Lloyd Brown" Doc responded, grinning. He took the car up into the air and flew out of the house, into the night sky. The car rapidly accelerated to 80, then remained stuck at that speed for roughly half a minute as they flew towards Clayton Ravine.

As they got there, Calvin cast a look at the RPI, which was stashed in the back. Although he still didn't entirely get how the device worked, Doc and Chris had given him some explanation, and from what he could figure out now, it was indicating that his full erasure was only several days away. He gulped, and turned back to the windshield as Doc resumed accelerating up to 88. His final thought as they kicked back in time was one of hope – hope that when they got to the past, his impending death would not be so impending anymore.