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When a Black Hole Dies, Is a White Hole Born?

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Do black holes die? And if so, what happens when they're gone?

A new theory suggests that these galactic vacuums hit a point at which they can collapse no further. At this moment, a black hole ceases to exist, and it explodes into its exact opposite: a white hole. Like a galactic purge, all the matter and light sucked in by the black hole is now spewed outward.

White holes aren’t new to the science world. Einstein hypothesized about their existence. But this new idea from theoretical physicists Hal M. Haggard and Carlo Rovelli [PDF] of Aix-Marseille University in France looks at how and why white holes might form. Their work is based on a few rules of quantum theory, which is a notoriously complicated field. To be brief, one approach says when you zoom in on the granular things that make up space-time, at the smallest level you’ll find tiny “loops” that can’t be compressed into anything smaller. A black hole forms when a dying star collapses on itself and its matter is condensed. Haggard and Rovelli say that, because these loops can’t get any smaller, they would halt the collapse, and produce outward pressure called a “bounce,” causing the black hole to explode into a white hole that can't let anything in.

This process happens almost instantaneously, in a few thousandths of a second. But because the gravitational pull of black holes “dilate” time, this process would appear to happen over billions if not trillions of years for outside observers. For example, the researchers think a black hole with the same mass as the sun would seem to us to take “about a thousand trillion times the current age of the Universe to convert into a white hole.”

All of this is theoretical at the moment—there’s no observational evidence of white holes. But if accurate, the findings could mean that some galactic flares are actually the last gasps of some really old black holes. And researchers would have an answer to a long-standing question: Can information escape a black hole? If white holes spit matter back out into the universe, the answer would be yes.

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Big Questions
Does Einstein's Theory of Relativity Imply That Interstellar Space Travel is Impossible?
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Does Einstein's theory of relativity imply that interstellar space travel is impossible?

Paul Mainwood:

The opposite. It makes interstellar travel possible—or at least possible within human lifetimes.

The reason is acceleration. Humans are fairly puny creatures, and we can’t stand much acceleration. Impose much more than 1 g of acceleration onto a human for an extended period of time, and we will experience all kinds of health problems. (Impose much more than 10 g and these health problems will include immediate unconsciousness and a rapid death.)

To travel anywhere significant, we need to accelerate up to your travel speed, and then decelerate again at the other end. If we’re limited to, say, 1.5 g for extended periods, then in a non-relativistic, Newtonian world, this gives us a major problem: Everyone’s going to die before we get there. The only way of getting the time down is to apply stronger accelerations, so we need to send robots, or at least something much tougher than we delicate bags of mostly water.

But relativity helps a lot. As soon as we get anywhere near the speed of light, then the local time on the spaceship dilates, and we can get to places in much less (spaceship) time than it would take in a Newtonian universe. (Or, looking at it from the point of view of someone on the spaceship: they will see the distances contract as they accelerate up to near light-speed—the effect is the same, they will get there quicker.)

Here’s a quick table I knocked together on the assumption that we can’t accelerate any faster than 1.5 g. We accelerate up at that rate for half the journey, and then decelerate at the same rate in the second half to stop just beside wherever we are visiting.

You can see that to get to destinations much beyond 50 light years away, we are receiving massive advantages from relativity. And beyond 1000 light years, it’s only thanks to relativistic effects that we’re getting there within a human lifetime.

Indeed, if we continue the table, we’ll find that we can get across the entire visible universe (47 billion light-years or so) within a human lifetime (28 years or so) by exploiting relativistic effects.

So, by using relativity, it seems we can get anywhere we like!

Well ... not quite.

Two problems.

First, the effect is only available to the travelers. The Earth times will be much much longer. (Rough rule to obtain the Earth-time for a return journey [is to] double the number of light years in the table and add 0.25 to get the time in years). So if they return, they will find many thousand years have elapsed on earth: their families will live and die without them. So, even we did send explorers, we on Earth would never find out what they had discovered. Though perhaps for some explorers, even this would be a positive: “Take a trip to Betelgeuse! For only an 18 year round-trip, you get an interstellar adventure and a bonus: time-travel to 1300 years in the Earth’s future!”

Second, a more immediate and practical problem: The amount of energy it takes to accelerate something up to the relativistic speeds we are using here is—quite literally—astronomical. Taking the journey to the Crab Nebula as an example, we’d need to provide about 7 x 1020 J of kinetic energy per kilogram of spaceship to get up to the top speed we’re using.

That is a lot. But it’s available: the Sun puts out 3X1026 W, so in theory, you’d only need a few seconds of Solar output (plus a Dyson Sphere) to collect enough energy to get a reasonably sized ship up to that speed. This also assumes you can transfer this energy to the ship without increasing its mass: e.g., via a laser anchored to a large planet or star; if our ship needs to carry its chemical or matter/anti-matter fuel and accelerate that too, then you run into the “tyranny of the rocket equation” and we’re lost. Many orders of magnitude more fuel will be needed.

But I’m just going to airily treat all that as an engineering issue (albeit one far beyond anything we can attack with currently imaginable technology). Assuming we can get our spaceships up to those speeds, we can see how relativity helps interstellar travel. Counter-intuitive, but true.

This post originally appeared on Quora. Click here to view.

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Big Questions
What Does the Sergeant at Arms Do?
House Sergeant at Arms Paul Irving and Donald Trump arrive for a meeting with the House Republican conference.
House Sergeant at Arms Paul Irving and Donald Trump arrive for a meeting with the House Republican conference.
Chip Somodevilla, Getty Images

In 1981, shortly after Howard Liebengood was elected the 27th Sergeant at Arms of the United States Senate, he realized he had no idea how to address incoming president-elect Ronald Reagan on a visit. “The thought struck me that I didn't know what to call the President-elect,'' Liebengood told The New York Times in November of that year. ''Do you call him 'President-elect,' 'Governor,' or what?” (He went with “Sir.”)

It would not be the first—or last—time someone wondered what, exactly, a Sergeant at Arms (SAA) should be doing. Both the House and the Senate have their own Sergeant at Arms, and their visibility is highest during the State of the Union address. For Donald Trump’s State of the Union on January 30, the 40th Senate SAA, Frank Larkin, will escort the senators to the House Chamber, while the 36th House of Representatives SAA, Paul Irving, will introduce the president (“Mister [or Madam] Speaker, the President of the United States!”). But the job's responsibilities extend far beyond being an emcee.

The Sergeants at Arms are also their respective houses’ chief law enforcement officers. Obliging law enforcement duties means supervising their respective wings of the Capitol and making sure security is tight. The SAA has the authority to find and retrieve errant senators and representatives, to arrest or detain anyone causing disruptions (even for crimes such as bribing representatives), and to control who accesses chambers.

In a sense, they act as the government’s bouncers.

Sergeant at Arms Frank Larkin escorts China's president Xi Jinping
Senat Sergeant at Arms Frank Larkin (L) escorts China's president Xi Jinping during a visit to Capitol Hill.
Astrid Riecken, Getty Images

This is not a ceremonial task. In 1988, Senate SAA Henry Giugni led a posse of Capitol police to find, arrest, and corral Republicans missing for a Senate vote. One of them, Republican Senator Bob Packwood of Oregon, had to be carried to the Senate floor to break the filibustering over a vote on senatorial campaign finance reform.

While manhandling wayward politicians sounds fun, it’s more likely the SAAs will be spending their time on administrative tasks. As protocol officer, visits to Congress by the president or other dignitaries have to be coordinated and escorts provided; as executive officer, they provide assistance to their houses of Congress, with the Senate SAA assisting Senate offices with computers, furniture, mail processing, and other logistical support. The two SAAs also alternate serving as chairman of the Capitol Police board.

Perhaps a better question than asking what they do is pondering how they have time to do it all.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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