Chapter 7
Theresa had parked a few hundred meters away from the abandoned factory. It was located in an industrial area which was hardly in use anymore and a normal person wouldn't even enter this district at bright daylight. Theresa locked her car and walked down the empty street when she suddenly heard a familiar noise. She had to smile instinctively when she turned around and saw the big, blue police box materializing in a dark alley.
"You took your time," she noted when the man calling himself 'The Doctor' opened the door and looked out. "What do you want?"
"Do you want to travel with me?" he asked and smiled at her.
"How comes your change of heart? And how much time has passed since we last met?"
"About an hour," he admitted.
"And the first question?" she wanted to know when she already came walking toward him.
"I...read your MI5 and SFPD files. You're...not what you seem to be. You got into the wrong hands...I think you should do better than live a constant life of lies..."
"And running away from all I know is better?"
"It's a time machine. You can come back whenever you want. So...would you like to travel with me?"
"How can I say 'no'?" she said and entered the TARDIS. "How big is it actually?"
"Infinite..."
"I don't th-...I can't imagine that," she said and climbed the stairs to the main console of the big, yellow-brown-green room.
"So, where do you want to go?"
"I don't know. You know time and space better than I do. What about the past this time?"
"Said and done," he answered and started to fly his space-time-ship.
About a minute later, they landed and the doctor shut off most of the engines. "1805, Switzerland," he said and accompanied her to the door.
She looked out first. "Sure?"
"No, actually not so much," he admitted and looked out himself. "Seems more like 1905."
"I'm not properly dressed. Don't you think they'll look at me strangely?"
"This door over there, go down the floor and the third door on the left, you'll find a wardrobe there," he instructed.
"You are amazing," she said happily and came back ten minutes later with a dress that better matched this time.
Together, they stepped out of the police box and entered the streets. "So, have you at least got the country right?" Theresa asked hopefully.
"Oh, I think so," The Doctor said and spotted someone at the other sight of the street. "Hey, Albert," he shouted and walked over to the man.
"Oh no, not you again, Doctor. I'm having quite enough to do these days," the man answered.
"Theresa, may I introduce you to Albert Einstein...Albert, that's my friend Theresa."
"Hello, young girl. I'm sorry but I'll have to go...working."
Theresa's mouth dropped open when she shook hands with one of the most brilliant heads of human history of science. "You...you're currently working on the Special Theory of Relativity, aren't you?" she asked.
"Oh, yes, my dear. People do talk, but I don't think that a girl like you should waste any time of thinking about such things. I have my problems already on my own..."
"What's your problem, Albert?" the Doctor asked interestedly.
Einstein first shook his head, but then gave up and started explaining, "imagine you have two rockets flying through space. In the first one, there's Bob and in the other one there's Alice."
"Now I know how these names ended up in all books," Theresa muttered under her breath and the Doctor smiled at her.
"Now, Alice is travelling with 0.5c and Bob with 0.7c. An observer who does not move, for example someone standing on a planet, sees those two with exactly this velocity. He's in system A. But Alice, flying in her rocket, is being passed by Bob. Because she has her own velocity, she does not feel herself moving and takes along that Bob is flying with 0.2c. She's system B, a moving observer."
"And where's the problem?" the Doctor asked.
"Alice thinks that she is not moving. She says Bob is flying with 0.2c. The observer on the planet says he is not moving. He says Bob is flying with 0.7c. Both can be correct. But even if I could write this down as I just explained it to you, how can I convert this into a mathematical scheme?"
"What about Lorentz-transformation?" Theresa asked, before she quickly turned to the Doctor, whispering, "am I in danger of creating a paradox?"
"No, it's just a predestination paradox, they happen all the time," he answered and Albert weirdly looked at them.
"You have two coordinate systems. One is not moving, the other one is moving with a constant velocity. At the point t=0, they're both at the same spot in the space-time. For example, if you are throwing a ball, you see it fly with 5km/h. Then, someone is on a train, throwing the same ball. The train is at the railway station and driving with 10 km/h. You throw the ball again with 5 km/h. An unmoving observer on the platform see the ball being thrown with 10 + 5 = 15km/h."
"This is simple. I've explored it ages ago...how do you know about it?" Einstein asked and then turned to the Doctor, "she's from the future, isn't she? Fascinating."
"What if you now had the same problem with rockets and they'd be flying with 0.7c and 0.5c. If you added them up, you'd get 1.2c."
"Which is not possible. I'd have to find a factor which can add these velocities without making the result bigger than the speed of light!" Einstein suddenly shouted. "You're a genius," he said and quickly kissed Theresa before he started running back to his flat.
"Oh, and Einstein," Theresa shouted after him, "if you describe factors, please take the symbols β and γ!"
"That's him," the Doctor muttered when Einstein was already out of sight.
"How can this work? I mean, I just explained him something that I learned from him," Theresa asked when they continued walking on.
"Predestination paradox. You were supposed to do that."
"Something can only be done, because it was done before...like in Star Trek IV. Kirk sells his glasses in the 20th century, after he received them as a gift by Bones in the 23rd century. Bones could only give him the glasses because Kirk had sold them 300 years ago."
"It's even more complicated when you really start to think about it. Just imagine, the same thing would pass its own timeline and exists twice or multiple times at once," the Doctor said.
"Oh my God..." Theresa muttered and they continued walking through the little town in Switzerland.
Well, some Physic freaks of you will notice that Theresa gave him the answer to another theory included in the STR and not to the one Einstein asked for. I'm sorry for this confusion...
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