Art by: Sofia Ayuso

What happens if someone time travels to the past and kills their grandfather before he had children?

In linear timelines that fix "the present" as a mid-point between past & future, the killer would cease to exist, therefore creating a paradox.

Other theories on time travel can potentially work around this paradox:

• Relativity links time & space so the faster you travel the slower you experience time (Einstein) .
• Quantum - every time one state, or outcome, is observed, there is another "world" in which a different quantum outcome becomes reality. (Many-Worlds Theory).

Art by Alex Gray

"Hilbert's paradox of the Grand Hotel AKA "Infinite Hotel Paradox" shows the counter intuitive property of infinite sets."

Thanks Wikipedia.

You have a hotel with an infinite set of rooms. Then an infinite set of guest arrive.

Will you have room for them all?

Yes. Why?

You simply move guest one to room two.

If more sets of infinite guests arrive simultaneously, you can still accommodate them all as long as you have at least one empty room.

Sounds like binary code to me...

Art by: Julia Maystruck

Schrodinger's Cat illustrates the paradox of quantum superposition: the idea that several quantum systems can exists in several quantum states at the same time.  

1. A cat 🙀 flask of poison 🧪 and radioactive substance ☢️ are sealed in a box 📦
2. Detecting any radioactivity means the flask shatters ☠️ killing the cat 😿
3. After a while quantum mechanics sees the cat as simultaneously alive & dead.

But once you open the box the cat is either dead OR alive (not both alive & dead). So at when did quantum superposition cease & reality start? 

The bartender says, "we don't serve your kind in here."

Two time travelers walk into a bar