You might be sick of this question, but planetary scientists aren't. According to a May 2018 op-ed by two astronomers in the Washington Post, the 2005 redefinition of the word "planet" that left Pluto in the dust should probably be reconsidered. Here's one of their points that really resonated with us: Under the current definition, a planet must have "cleared its neighborhood," meaning it must have either deflected or accumulated all of the space debris in its orbit. Pluto fails on that end, but so did the Earth for the first 500 million years of its existence. It also suggests that if you were to pluck the Earth from its orbit and move it to the asteroid belt, it would somehow not be a planet anymore.

Lest you think these are just diehard Pluto fanatics who can't let the dream die, consider that Alan Stern, one of the authors of the piece, is also the principal investigator of the New Horizons probe, which swung by our outermost neighbor in 2015.

Dead is dead, right? Wrong. There are a lot of different ways to define death, and they don't always line up with each other. Is it when your heart stops beating? Well, that's certainly not good for you, but then there are "beating heart cadavers" who are completely brain dead, but whose organs still function. Plus, medical technology can go a long way toward keeping certain organs going. Are you dead when your heart stops beating and when your lungs stop working, or when both have degraded so badly that not even life support can support you? Speaking with Time, Dr. James Bernat said that the traditional definition of death requires all three elements: circulatory failure, respiratory failure, and not being on life support.

Viruses have been considered many things in the 100+ years since their first discovery — poisons, life forms, biological chemicals, and life forms again. The fact is that scientists can't quite decide if they're alive or not, since they're capable of reproduction but only by hijacking the processes of bonafide living cells. Still, they certainly do what they can to preserve their genetic material, and they certainly are beneficiaries of natural selection. So are they living or not? Well, in 2004, virologist Marc Regenmortel summed it up quite poetically: "They are nonliving infectious entities that can be said, at best, to lead a kind of borrowed life."

We already told you about the Bone Wars, an absurd, 15-year rivalry between a feuding paleontologists Othniel Charles Marsh and Edward Drinker Cope. But what you might not have known is that for many years, everyone's favorite childhood dinosaur, the Brontosaurus, was considered a casualty of their wars. What happened was that Marsh dug up one set of bones in 1877 and called the animal "Apatosaurus," then dug up another set two years later and named that animal "Brontosaurus." But in 1903, another paleontologist named Elmer Riggs convinced the dinosaur community that these were, in fact, two versions of the same animal, and thus the older name won out. Which is too bad, since "Brontosaurus" rolls off the tongue so much more easily. But another analysis in 2015 revealed a number of substantial differences between the two specimens, giving Brontosaurus the chance to lumber back into the taxonomy.

Pretty much everyone agrees that some form of the Big Bang happened. The only question is, what happened beforehand? Unlike a lot of the other items on this list, the answer to the question isn't a matter of recategorizing old concepts or accepting a little bit of ambiguity — it has a real answer that we're not likely to ever prove definitively. Perhaps our universe sprung out of another, older one. Perhaps our Big Bang was just one of several similar spatial expansions, each one exploding into its own universe-in-a-bubble. Or maybe we're all living on a giant space turtle. While it's unlikely we'll ever know, science can get us closer to the true answer.

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See what theories today's leading scientific minds want to get rid of in "This Idea Must Die," featuring essays by Richard Dawkins, Martin Rees, Nina Jablonski, and Sherry Turkle. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.