Of all the astronomical phenomena you can witness, the total solar eclipse has to be the most visceral--the most in-your-face reminder that our reality consists of giant balls of rock spinning around stars. It's also the eclipse and phenomena like it that set us on the path to understanding that reality in the first place.

The Moon has been one of the most important theoretical stepping stones to our understanding of the universe. We’ve long understood that it could also be our literal stepping stone: humanity’s first destination beyond our atmosphere.

Meet Alice and Bob, famous explorers of the abstract landscape of theoretical physics. Heroes of the gerdankenexperiment—the thought experiment—whose life mission is to find contradictions in the deepest layers of our theories. Today our intrepid pair are jumping into a black hole. Again. Why? Well, to determine the fundamental structure of spacetime and its connection to quantum entanglement of course.

In the far future we may have advanced propulsion technologies like matter-antimatter engines and compact fusion drives that allow humans to travel to other stars on timescales shorter than their own lives. But what if those technologies never materialize? Are we imprisoned by the vastness of space—doomed to remain in the solar system of our origin? Perhaps not. A possible path to a contemporary cosmic dream may just be to build a ship which can support human life for several generations; a so-called generation ship.

Black holes are inevitable predictions of general relativity—our best theory of space, time and gravity. But they clash in multiple ways with quantum mechanics, our equally successful description of the subatomic world. One such clash is the black hole information paradox—and a proposed solution—black hole complementarity—may forced us to radically rethink what it even means to say that something to exists.

Cern's Large Hadron Collider routinely collides particles at energies equivalent to a fraction of a second after the Big Bang. If this worries you, then the following fact will either put you at ease or scare the hell out of you. And that's that a particle with the energy of an LHC collision hits every square kilometer of the Earth every single second. And we only relatively recently figured out where these cosmic rays are coming from.

So you’ve decided to jump into a black hole. Good news: as long as the black hole is big enough you can sail through the event horizon without harm and get to experience the interior of the black hole before you’re annihilated by the central singularity. Or so we once thought. These days, quite a few physicists believe that the only way to avoid horrible contradictions in fundamental physics generated by black holes is for all them to be surrounded by screens of extreme energy that prevent anything from ever entering the event horizon. Sounds outlandish? Welcome to black holes. So let’s find out why many of our most brilliant physicists take these black hole firewalls deadly seriously.

The primary characteristic that defines black holes is in the name. Black holes are black. The gravitational pull at the event horizon is so powerful that not even light can escape. In this case, black means absence of light. We also think of black as indicating absence of colour. But it turns out there is a way to make a coloured black hole—as long as by colour you mean quantum chromodynamic charge.

The holy grail of theoretical physics is to find the long-sought theory of quantum gravity. But what if this theory is as mythical as the grail of legend? What if gravity isn’t weirdly quantum at all, but rather … just a bit messy? Or random? So says the postquantum gravity hypothesis of Jonathan Oppenheim.

If we discover how to connect quantum mechanics with general relativity we’ll pretty much win physics. There are multiple theories that claim to do this, but it’s notoriously difficult to test them. They seem to require absurd experiments like a particle collider the size of a galaxy. Or we could try to physics smarter, instead of physicsing harder. Let’s talk about some ideas for quantum gravity experiments that can be done on a non-galaxy-sized lab bench, and in some cases already have been done.

If you track the motion of individual stars in the ultra-dense star cluster at the very center of the Milky Way you’ll see that they swing in sharp orbits around some vast but invisible mass—that’s the Sagittarius A* supermassive black hole. These are perilous orbits, and sometimes a star wanders just a little too close to that lurking monster, leading to its utter destruction in the spectacular phenomenon known as a tidal disruption event. We’ve never seen a TDE in the Milky Way, but we’ve seen them in distant galaxies—and we now know how to spot stellar destructions so extreme that they reveal properties of the black hole itself.

Here’s the story we like to tell about the beginning of the universe. Space is expanding evenly everywhere, but if you rewind that expansion you find that all of space was once compacted in an infinitesimal point of infinite density—the singularity at the beginning of time. The expansion of the universe from this point is called the Big Bang. We like to tell this story because it's the correct conclusion from the description of an expanding universe that followed Einstein's general theory of relativity back in the 19-teens. But since then we've learned so much more since then. Does our modern understanding of the universe still insist on a point-like Big Bang? Recent work actually gives us a way to avoid the beginning of time.