I held it at arms length. A scruffy business card in battered Russian. Something like “путешествие во времени”
(“puteshestviye vo vremeni” in my mother tongue. It had been a long time. I was rusty.)
“So, you’re telling me th…”

“That time travel is possible. Probable. Inevitable. Yes.”

“Ok, old man. I’ll give you a beer. Spill…”

“Well, Sonny… that would be a waste of good beer.” The ‘old man’ smiled. “Yes, yes. I know what you mean.” He shrugged.

“We know the universe is expanding, right? And that expansion is accelerating, yes?”

“Dark energy.” I snorted.

“Precisely, and no one knows what the accelerating force is. But, what if it is negative mass, formed at the creation of the universe? What if, by chance the negative mass coalesced at the centre, and drove all the mass we know out into the universe we can see?”

“Negative mass… means negative energy… and that could mean stable worm holes!” I cried. “That’s genius. Except one thing. How do we make something with negative mass?”

The old man shook his empty glass knowingly. “That will cost you another round.”

Once he had his refill he whispered “Well you have to create a space of Zero Energy. Truly ZERO energy. Then, with luck, and the right conditions, mass and negative mass will form. Bakh!”

“But that will cost… nothing at all!” I looked confused. “If that’s so, why hasn’t anyone done it already?”

My future self sipped. “What makes you think it hasn’t?” He slurred.