What is the big rip, and can we stop it?

a colorful whirlpool swirls in space
Will the universe end in a 'big rip'? It depends on phantom energy. (Image credit: Getty Images/Mark Garlick/Science Photo Library)

Imagine a future where the universe, all too soon, tears itself apart. Eventually, space-time is torn asunder, rendering the universe uninhabitable. 

Imagine a future where the universe, all too soon, tears itself apart. First come the clusters, with their galaxies pulled away from each other. Then, the galaxies dissolve. Then the star systems and the planets. And then atoms themselves. Eventually, space-time is torn asunder, rendering the universe uninhabitable. 

This is a potential future known as the Big Rip. It sounds scary and almost impossible to imagine, but the truly horrifying part is that some evidence seems to be pointing directly toward that fate.

Related: Was Einstein wrong? The case against space-time theory

Phantom energy 

A quarter century ago, astronomers discovered dark energy, which is the name given to the apparent accelerated expansion of the universe. This dark energy is deeply mysterious; we do not currently understand what causes it, where it came from or what it's going to do. But that hasn't stopped theorists from guessing.

The simplest thing dark energy could be is a so-called cosmological constant. In this simple picture, dark energy is a substance that permeates all of space and time. There's dark energy everywhere, including in the room you're in right now. This dark energy is perfectly constant. It's exactly the same all through space and time. This substance causes the expansion of the universe to accelerate, but otherwise, it never changes.

Another possibility is that the substance behind dark energy can double back on itself, causing itself to amplify with time. This situation is known as phantom dark energy (or just phantom energy). In this case, the acceleration would go up with time. 

Read more: 25 years after its discovery, dark energy remains frustratingly elusive

Ghosts in the machine 

This ramping up of the acceleration, ironically, would make the observable universe far smaller. That's because the velocity between any two points would continue to grow, even beyond the speed of light. In this scenario, galaxies would fly away from each other so quickly that they would never see each other again. This would make the observable limit of what we could see shrink with time in an uncontrolled way.

If two points were ripped apart faster than light, they would no longer interact through any force of physics. Whereas a constant dark energy would leave behind already-intact objects, like clusters of galaxies, phantom energy could tear them apart. In a finite amount of time, billions of years from now, clusters would tear apart, followed by ever-smaller objects. Even atomic and nuclear bonds would not withstand the onslaught.

Eventually, space itself would dissolve in an event known as the Big Rip. Any two points, no matter how close, would be ripped infinitely far away from each other. The very structure of space-time, the causal foundations that make our universe work, would no longer behave. The universe would just break down.

However, luckily, most physicists do not believe this scenario can actually happen. For one, it's unclear how this process of ripping interacts with the other laws of physics. For example, quarks cannot be torn apart — when you attempt to do so, you need so much energy that new quarks materialize out of the vacuum. So ripping apart quarks just might lead to other, interesting interactions.

Also, phantom energy doesn't behave according to normal physics. To make this work, the phantom substance has to have negative kinetic energy. But negative kinetic energy usually doesn't happen in the universe — an example of this would be a ball naturally rolling uphill — so this would be a pretty major exception to our established understanding of physics.

An artist's conception of dark matter scattered throughout the universe. (Image credit: Getty images)

Evidence for the Big Rip 

For decades, astronomers have been attempting to measure the strength of dark energy. They do this through a number known as the equation of state parameter, which, for the dark energy substance, measures the ratio of its pressure to its energy density. A cosmological constant corresponds to a parameter equal to -1, while a phantom energy scenario is anything with this parameter being less than -1.

So far, all astronomical measurements are compatible with a cosmological constant, an equation of state parameter of -1. But strangely, all those same measurements, year after year, prefer a value slightly less than -1. All of those measurements have uncertainties, which include the "boring" case of a cosmological constant, but it's intriguing that the data seem to prefer a phantom energy universe.

Some physicists believe that further evidence will pull us away from the phantom scenario, firmly into the safety of a cosmological constant. Others, however, are taking this as a sign that the universe might be telling us something interesting. Perhaps there is some combination of physics allowed by current laws that gives the appearance of phantom energy. (For example, if you kick a ball hard enough, it can temporarily go uphill.) Or perhaps there are some brand-new physics that seem impossible now but will make sense with new understanding.

But even if we do have a phantom energy scenario, it's not like the universe is going to tear itself apart anytime soon. With the known measurement constraints, the Big Rip wouldn't play out for hundreds of billions of years. So, in the meantime, we can enjoy the nice, calm, steady cosmos.

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Paul Sutter
Space.com Contributor

Paul M. Sutter is an astrophysicist at SUNY Stony Brook and the Flatiron Institute in New York City. Paul received his PhD in Physics from the University of Illinois at Urbana-Champaign in 2011, and spent three years at the Paris Institute of Astrophysics, followed by a research fellowship in Trieste, Italy, His research focuses on many diverse topics, from the emptiest regions of the universe to the earliest moments of the Big Bang to the hunt for the first stars. As an "Agent to the Stars," Paul has passionately engaged the public in science outreach for several years. He is the host of the popular "Ask a Spaceman!" podcast, author of "Your Place in the Universe" and "How to Die in Space" and he frequently appears on TV — including on The Weather Channel, for which he serves as Official Space Specialist.

  • MarkmBha
    Can humans on planet Earth stop the universe from destroying itself?
    Are you serious?
    Reply
  • Unclear Engineer
    You know it's click bait when the headline says "can we stop it?"

    The whole "inflation" theory has so many inconsistencies that I have my doubts about our basic understanding of our astronomy observations.

    For instance, if inflation is a scale factor for space, then why are we not seeing something like the wavelengths of photons emitted by atomic transitions still "fitting" those atoms after some amount of inflation? Instead, we are seeing what we ascribe to electron orbit transitions in hydrogen getting stretched into microwave dimensions. Why haven't the atoms stretched along with their emitted photons? Even the components of atoms must have stretched at some point if we believe the Big Bang Theory's inflation concept, because the whole universe is theorized to have been only as big as an atom is today, just after the Big Bang. It looks to me like the theorists want to "have it both ways", stretching some things to match observations while not stretching other things to match other observations.
    Reply
  • Fire-Starter James
    Unclear Engineer said:
    You know it's click bait when the headline says "can we stop it?"

    The whole "inflation" theory has so many inconsistencies that I have my doubts about our basic understanding of our astronomy observations.

    For instance, if inflation is a scale factor for space, then why are we not seeing something like the wavelengths of photons emitted by atomic transitions still "fitting" those atoms after some amount of inflation? Instead, we are seeing what we ascribe to electron orbit transitions in hydrogen getting stretched into microwave dimensions. Why haven't the atoms stretched along with their emitted photons? Even the components of atoms must have stretched at some point if we believe the Big Bang Theory's inflation concept, because the whole universe is theorized to have been only as big as an atom is today, just after the Big Bang. It looks to me like the theorists want to "have it both ways", stretching some things to match observations while not stretching other things to match other observations.
    Right on. The atoms do not stretch, so why think the photons do? The Doppler effect is a sufficient explanation for the redshift due to expansion. Another big question is: why is motion due to The Expansion exempt from relativity? It's a fundamental unspoken assumption in this article.

    Unclear Engineer, you have stimulated me into doing a write-up on this. Seems like a good reason to put off mowing. :)
    Reply
  • Classical Motion
    If Doppler is the only explanation of shift, then the outer galaxies are moving at multiple c velocities.

    Are you satisfied with that result? So mass can move much faster than c? Isn't that against the laws of physics?

    That shift is a measurement that should not be. An impossible measurement.

    Is it that easy to disregard a pillar of science?

    It tells me that something is FUNDAMENTALLY wrong with our theories. OR with our measurement.
    Reply
  • Hardcrunchyscience
    MarkmBha said:
    Can humans on planet Earth stop the universe from destroying itself?
    Are you serious?
    Yellow journalism headlines, the wave of the present and future. Monetized by clicks. "Can we stop it!?" I weep.
    Reply