She's excited, and decides now is a good time for an infodump

For a moment, Sam simply stared at the screen, the gears turning in her head. Time seemed to stand still for Roy, as he awaited her reaction.

"So... that's you, and the redhead next to you... is me." She stepped back, and flopped down at the desk, the old computer chair squeaking as she did so. "That's... that's..."

Roy braced himself for the worst. He could only imagine what was going on in her head right now. Questions about her own nature as a human being, and the nature of the universe, was a sure catalyst for an existential crisis...

"THAT'S AWESOME!" she suddenly shouted, startling Roy from his own thoughts. She jumped up from her chair, sending it flying against the wall, her entire body radiating exuberance. "IT WORKED! IT WORKED! The guys on the forums, the professors at school, they all said I was crazy to even try, but now I'll show them! I'll show the WORLD!"

Roy was beginning to get a little scared. Apparently, Sam had gone full Victor Frankenstein. And you never go full Frankenstein.

"Calm down, Sam," he tried to reason as she kept shouting about her theories and what this meant for Science, "We need to talk about this! I accidentally turned you into a girl!"

That made Sam pause for a moment, before she regarded Roy with a smile. "That's right, you think I've always been a boy." She chuckled slightly. "I really must apologize, Roy, but I suppose I should explain exactly what the Retroactive Timeline Manipulation Device is capable of."

Roy nodded along with her, trying desperately to find any shred of sanity to cling to in this moment.

"You see, it doesn't really send anything back in time, as that would be impossible," she explained. "As anyone with a passing interest in relativity would know, you can only travel forward, and even then, it would require you to travel through space at near light speeds."

Roy continued nodding, having learned at least a little bit about the subject from years of watching sci-fi movies with Sam.

"Rather, it creates short-lived temporal pocket universe, wherein the person is transported, then quickly transformed, using Retroactive Genetic Manipulation, or RGM, as I've come to call it, into an alternate version of themselves! This alternate form is defined by a set of chronometric operations, simplified into the parameters in the options that you... carelessly randomized." Roy had to cringe at that, but Sam was quick to assuage his guilt. "I'm not upset about that, you've simply helped me troubleshoot the randomize function a little bit early. It's fine, really."

"Wait," Roy interjected, "doesn't that mean you're not my Sam, but a Sam from another universe?"

"Oh, no, not at all! But that's where the second part of the device comes in! As the new subject is pulled into the unfamiliar pocket universe, the two universes make room for them, by sending chronotons from the pocket universe into the original universe! But as chronotons are a five dimensional particle, they exist simultaneously in all eras of the timeline. And as they've already been manipulated by the RGM, they result in a Temporal Cascade, or TC, which then merges the timelines, of both the pocket universe and parent universe! This makes it so that their new form or personage has always existed in the parent timeline." As she moved on to her next point, her face scrunched up in consternation. "The only problem is, my calculations had previously shown that anything within a close proximity of the device, including the subject in question, would be protected from the RTR, thanks to a quantum shielding effect I worked into the construction. I suppose that's what I get for cribbing equations from 420NoScope on the temporal physics forums," she finished, sighing dramatically.

Roy was... absolutely lost. "So... are you Sam? Or... are you... not Sam?"

Sam could not help but chuckle. "Yes, I'm Sam. Well, I'm Samantha Elvira Haddonfield, to be precise. Now, if you would indulge me, Mr. Royland Archibald Springwood," she said, eyeing him with excitement in her eyes, "I think I have some questions for you."