Could the Universe End by Tearing Apart Every Atom?

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Matt O'Dowd (1:00)

Of all the unlikely ends to the universe, the Big Rip has to be the most spectacular. Galaxies ripped to shreds, stars obliterated, cats and dogs living together and then tragically separated by the infinitely accelerating expansion of space on subatomic scales. Good thing it's not going to happen. Or is it?

The universe is expanding, and that expansion is accelerating. We don't know what's causing that acceleration, but that hasn't stopped us from giving it a name. We call this unknown influence dark energy. The observed acceleration is, for the most part, nicely described with a constant density of dark energy. The same amount of this stuff in every block of space. Which means, if you increase the volume, you increase the overall amount of dark energy. Hence, the accelerating expansion. Mathematically, we describe a constant energy density with the cosmological constant in the equations of Einstein's general theory of relativity. But what if dark energy is not constant? What if the energy density in each patch of space increases over time? In that case, the acceleration itself would be accelerating.

That would be bad. As long as the rate of acceleration doesn't increase, the accelerating expansion of the universe isn't a big deal. At least for those of us safe and sound in nice galaxies like the Milky Way.

Here, the galaxy's gravitational field is plenty strong enough to resist the minuscule effect of dark energy.

It's in the vast tracks of space between galaxy clusters over countless trillions of cubic light years of emptiness that dark energy adds up. The sum of this outward push ultimately overcomes the inward gravitational pull between the galaxies. Galaxies will eventually be so far apart that they can't see each other, let alone feel each other's gravity. But as long as dark energy doesn't increase, there will be no expansion inside those lonely galaxies. They will be safe to fade to heat death, as we cheerily discuss in this episode. And in fact, that's probably what will happen. But it's fun to think about even worse case scenarios. Also, there's a tiny bit of very circumstantial evidence that we might not be so safe from dark energy after all.

But before we get to the potential disaster of an increasing dark energy and the Big Rip that follows, let's do a quick refresher on how dark energy works in the language of Einstein's general relativity. I say refresher because we spent a whole playlist delving into the mysteries of dark energy. We actually used math, the Friedman equations. We're not going to go so deep here, but we are going to take a quick mathy detour. Feel free to review that playlist before or after if you're...

SPEAKER_1 (4:00)

You know those tiny back to school emergencies somehow become your problem? That's why I love Uber Eats. You can order school supplies, snacks and lunchbox essentials for $5 or less. So when your kid casually drops, I don't like peanut butter anymore or I need five green highlighters for a project due tomorrow. Uber Eats has you covered. Get everything you need for back to school today from your favorite brands like Albion Staples and Uber Eats. Order now.

N's 9-7, $5 or less before taxes and fees. Select items only, availability varies. See app for details.

SPEAKER_2 (4:31)

When you need to build up your team to handle the growing chaos at work, use Indeed Sponsored Jobs. It gives your job post the boost it needs to be seen and helps reach people with the right skills, certifications and more. Spend less time searching and more time actually interviewing candidates who check all your boxes. Listeners of this show will get a $75 sponsored job credit at indeed.com/podcast. That's indeed.com/podcast. Terms and conditions apply. Need a hiring hero? This is a job for Indeed Sponsored Jobs.