This is my first venture into hard science fiction. I've done meticulous research and I'm pleased with the result. Let me know what you think in the comments.
Twelve year old Billy Marshall knocked on his uncle's front door. Milton Zuckerman lived in a nondescript house on a nondescript cul de sac in a nondescript suburb. Some said that Zuckerman's house was conspicuously nondescript given his reputation as a mad genius. Still, except for the occasional sound of electrical buzzing or sirens from his basement, he kept to himself and paid his taxes so the neighbors left him alone.
The door flew open. Zuckerman's snow white hair was disheveled, his beard a tangle, his lab coat stained with coffee, wine, and other substances Billy preferred not to guess at.
"Hmm? Yes? Yes? Who's there? Who... oh! It's you nephew," Zuckerman said, finally looking down at Billy.
"Hey Uncle Milton," Billy said.
"Is there something I can do for you? Hmm?"
"We were going out for lunch today, remember?"
"We are? Wait..." Zuckerman reached into his lab coat pocket and removed a smart phone. "Let's see... oh my goodness gracious! Wednesday already? And here I thought it was still last Friday. Well, come in, come in, give me a minute to get ready."
Billy followed his uncle inside. As usual, Zuckerman's house was a riot of overflowing bookshelves, loose papers, bubbling chemistry equipment, and humming machinery arranged without any rhyme or reason Billy could see. He pushed some books and half eaten pizza slices off of a couch in the living room and sat down to wait.
Zuckerman appeared, now wearing a blazer and a flat cap. "So where we headed nephew?"
"How about burgers?"
"Splendid," Zuckerman said. To him, food was simply fuel to keep his biological mechanisms ticking. "Follow me Billy."
They stepped into the garage. Next to Zuckerman's old Lincoln Town Car was a new machine Billy had never seen before. It was a capsule leaning upright against the wall and large enough to hold an adult human being. Attached was a console with colorful buttons, gauges, needles, and electrical conductors.
"What's that Uncle Milton?" Billy asked. "Did you just build it?"
"Oh yes. You see Billy, that is my time machine."
Billy's eyes grew wide and his jaw dropped. "Wow! That's so cool! A real time machine Uncle Milton? How does it work?!"
"It doesn't. Time travel into the past is impossible. You can go into the future but it's a one way trip and by the time you wake up, everyone and everything you ever knew or loved will be dead. If you ever woke up at all that is."
Billy seemed to deflate a bit. "Oh. That's... that's kind of depressing."
"Isn't it? Let's go get lunch."