October 31, 1985
4:15 PM PST
As soon as Doc landed the DeLorean back in 1985, and parked it into Hill Valley Park - Doc and the teens stepped out, and sat at a picnic table. Nobody else was around, so Doc figured that it was okay for them to discuss time travel.
"Okay, Jennifer," Doc said, sighing, "I suppose I should explain to you why Marty has been distracted. This would definitely help you to understand Marty a bit better."
"All right, Doc, what is it?" Jennifer asked, perking up.
"Okay, I must warn you," Doc informed Jennifer, "it's kind of a long story - and you also have to be thinking fourth-dimensionally."
"What does that mean?" asked Jennifer, confused. "Fourth-dimensionally?"
"Okay, Jennifer," Doc asked, sighing, "how good of an imagination do you have?"
"Well, I'm pretty imaginative," Jennifer said, smiling.
"Okay," said Doc, taking a deep breath, "in order to understand the concept of a fourth spacial dimension, imagine yourself as a two-dimensional creature - living on the surface of a piece of paper. Are you still with me?"
"Yeah, Doc," replied Jennifer, smiling, "I think I've got it."
"Okay, then," continued Doc, "there are sheets of paper above and below you. However, as a two-dimensional creature living on the surface of a piece of paper, you would not be aware of the fact that the paper you're living on exists in a three-dimensional universe - because your field of vision would be limited to the surface, or the length and width of the paper."
"Okay, Doc, I'm imagining," said Jennifer. "Continue on."
"Therefore," continued Doc, "you would not be aware of the existence of the dimension of height - or the third spatial dimension - because you would not have the ability to look in the direction of a third spatial dimension."
"Okay, I think I understand what you're getting at," said Jennifer, thoughtfully.
"So, by that analogy," explained Doc, "just like the hypothetical two-dimensional creature I postulated to you, the field of vision of three-dimensional beings - which would include us - would be limited to the 'surface' of a three-dimensional space, manifold with respect to a fourth spatial dimension."
"Okay, I'm still following you," Jennifer said, sighing a little.
"This means that we, as three-dimensional beings, would not be aware of the existence of a fourth spatial dimension," continued Doc, "because we cannot 'look' in the 'direction' of a fourth spatial dimension."
"So, Doc, are you saying that time would be the fourth dimension?" asked Jennifer.
"Precisely," replied Doc. "Now that you understand, I can begin explaining to you about Marty."
"All right, then," replied Jennifer. "Go on."
"Okay, then," explained Doc, "in the early morning of October 26, I revealed the time machine to Marty. However, because I borrowed plutonium from a Libyan terrorist group to fuel the time machine - and I didn't make them the nuclear bomb that I had promised, they decided to come after me. Thewy then tried to gun me. As Marty was driving away from the terrorists, he landed back in November 5 of 1955 - which happened to be the same day that I hit my head on the sink, and came up with the idea for the flux capacitor."
"Whoa! Whoa! Whoa!" protested Jennifer. "Let's back up here! Why did you make a deal with a group of terrorists, and where was Calvin?"
"I'm getting to that, Jennifer," Doc said, gently. "Now here's where you need to think fourth-dimensionally. When Marty went back to 1955, he had no memories of this timeline. He came from a timeline where I was shot dead, Lone Pine Mall was Twin Pines Mall, Biff Tannen still bullied Marty's father, and Calvin didn't even exist."
"Whoa, Doc," breathed Jennifer, "this is heavy!"
"Anyway," continued Doc, "back in 1955, Marty wrote me a letter - warning me that I would be shot be terrorists. Initially, I just tore up the letter - because I figured that I shouldn't know too much about my future. Luckily, though, I soon thought to tape the letter back together - and now I'm glad that I did, as was Marty. I then had to see to it, that I befriended Marty - some twenty to thirty years into the future. When I met Marty, I was surprised to find out that he had a twin. That's when I suspected that things were different. In 1955, Marty had shown me a picture of himself with his older brother and sister - but no twin. I also remembered what Marty told me about his father, and how he never stood up to Biff. I was somewhat good friends with George, who I knew was an aspiring science fiction writer - and also that he routinely hired Biff to wax the family car."
"Whoa!" breathed Jennifer. "That is a little too much to take in."
"Anyway, to cut to the chase," said Doc, "I had to see to it that Marty would arrive back in 1955 on the same day, in order to prevent a paradox from happening. That's also why I didn't invite Calvin. That's why I put on a bullet-proof vest, and went ahead with doing the test at the mall. The gunshot did knock me out a bit, but I came to about half an hour later. Then I heard Marty crying next to me. I felt so bad about the hell I had put him through."
"Okay, so what happened next?" asked Jennifer.
"Well, when Marty woke up the next day," explained Doc, "he initially had no memory of this timeline. He didn't even remember who Calvin was. However, as we were in 2015, saving the children of Marty and Calvin from going to jail - Marty's memories slowly began returning to him. As a result, Marty now has two sets of memories."
"Whoa!" gasped Jennifer. "That must be very confusing for him!"
"Right," replied Doc, "and that's why Marty was so distracted."
"Oh, okay," said Jennifer, as a look of understanding crept across her face. "I now understand why he was distracted, and why he couldn't tell me. I feel so sorry now, for breaking up with him. I'm certainly glad that my grandma convinced me to make up with him."
"Right, now you get it," Doc said, smiling. "Well, I think you guys better head home - and get ready for the Halloween party. You guys should change back into your own clothes, first."
"We will, Doc," said Jennifer, smiling.
Doc then embraced all three teens.