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Pulsed Plasma Thrusters

While travelling in space, one of the hardest things to do is to stop or change direction. Without anything to push against or friction to slow things down, spacecraft need to do all the hard work of changing their speed or path by there thrusters. And sometimes they do that in ways you would never expect: like by vaporizing Teflon. They are called pulsed plasma thrusters and they can use the same stuff that’s on your frying pan to make spacecraft zoom around the universe. And they have been doing it since the 1960s.

To make basically any move in space, satellites rely on Isaac Newton’s famous Third Law of Motion, which is probably on a poster in every high school physics classroom: For every action, there is an equal and opposite reaction. Put another way: throw stuff backwards and you will go forward. In fact, you can boil down every rocket design, no matter how complicated, to this basic idea. When thinking of a rocket, you might normally imagine the chemical propulsion. That’s the “fire-coming-out-the-end” kind, which uses a controlled explosion to hurl material out the back of the rocket. 

But once in space, another kind, electromagnetic or EM propulsion, also becomes available. They are not strong enough to get rockets off the ground, but they are great once you are past most of Earth’s atmosphere. These rockets work kind of like railguns, accelerating charged particles or ions, out the back with electric or magnetic fields. Today, we have all kinds of EM thrusters, but pulsed plasma thrusters, or PPTs, were the first ones ever flown in space.

They were used in 1964 on the Soviet Zond 2 mission to Mars. Like some other engines, PPTs specifically use plasma to generate thrust, instead of a random collection of ions. Plasma is a super hot substance made of charged ions and it is the fourth state of matter. In some ways, it behaves kind of like gas, because its atoms are pretty spread out. But unlike the other states of matter, plasmas can be shaped and directed by electric and magnetic fields.

To generate its plasma, PPTs eat Teflon! Which is pretty awesome. A pulsed plasma thruster places a block of Polytetrafluoroethylene what we know as Teflon between a pair of metal plates. Then, connected wires charge up those plates with electricity until it arcs through the Teflon block, set off by a spark plug. That arc delivers thousands of volts into the block, vaporizing the nearby Teflon and ionizing it into a plasma. The sudden burst of plasma effectively creates a circuit connecting the metal plates, which allows electricity to flow like it is travelling through a wire.

One neat side effect of flowing electricity is that it generates a magnetic field. And everything in the thruster is already arranged so that this field pushes the plasma out into space. At this point Newton’s third law springs into action, pushing the spacecraft in the opposite direction of the departing particles.

Well, this kind of thruster produces a very tiniest bit of motion. A pulsed plasma thruster deployed by NASA in 2000 produced an amount of force equal to the weight of a single Post-it Note sitting on your hand. Which might not seem that exciting, but it has some big implications. Like other forms of electromagnetic propulsion, these engines require a lot of electricity to run, but in exchange, they offer incredible efficiency with their fuel.

Pulsed plasma thrusters can produce up to five times more impulse or change in momentum for every gram of fuel than a typical chemical rocket. They do it very, very slowly, but they get the job done. PPTs also offer exceptional simplicity and safety. The only “moving part” is a spring that constantly pushes the Teflon block forward and without the need to store pressurized liquid or gas fuel, there is no chance of explosion. So it makes sense then that pulsed plasma thrusters were so useful back in the 1960s. Since then, their lack of power has meant that most spacecraft main engines have remained chemical. And when companies really need some kind of EM drive like for the Dawn mission to the asteroid belt they will tend to choose more sophisticated designs. But that doesn’t mean we are done with these thrusters just yet.

Recently, their extreme simplicity has made them a natural fit for the most up-and-coming field of exploration: CubeSats. CubeSats are tiny, shoebox-sized satellites designed for simple missions and built on the smallest of budgets often by research labs or universities. Earth-orbiting CubeSats seem almost tailor-made for the strengths of pulsed plasma thrusters. Lots of sunlight gives them ample electric power, but since they are so small, space and weight are at an absolute minimum. And right now, most CubeSats typically don’t have any kind of propulsion system of their own.

So one solution is micro pulsed plasma thrusters, which can weigh just a few hundred grams and measure under 10 centimetres on a side. That might not sound like much, but even a tiny amount of thrust could double the useful life of some kinds of CubeSats. They will likely need to undergo more testing and development before they are ready for primetime, but someday, we could have a whole fleet of Teflon-eating satellites.

Also Read:-  Let's Understand Black Hole

Let's Understand Black Hole

Black holes are among the most fascinating objects in our universe and also the most mysterious. A black hole is a region in space where the force of gravity is so strong not even light the fastest known entity in our universe can escape. 

The boundary of A black hole is called the event horizon a point of no return beyond which we truly can not see. When something crosses the event horizon it collapses into the black hole's singularity an infinitely small infinitely dense point for space-time and the laws of physics no longer apply.

Scientists have theorized several different types of black holes with stellar and supermassive black holes being the most common. Stellar black holes form when massive stars die and collapse the roughly 10 to 20 times the mass of our Sun and scattered throughout the universe. There could be millions of these Stellar black holes in the Milky Way alone. 

Supermassive black holes are giants by comparison measuring millions even billions of times more massive than our Sun. Scientists can only guess how they form but we do know they exist at the centre of just about every large galaxy including our own. Sagittarius a the supermassive black hole at the centre of the Milky Way has a mass of roughly 4 million Suns and has a diameter about the distance between the earth and our Sun.

Because black holes are invisible the only way for scientists to detect and study them is to observe their effect on nearby matter. This includes accretion disks, a disk of particles that form when gases and dust fall toward a black hole. And quasars Jets of particles that blast out of supermassive black holes.

Black holes remained largely unknown until the 20th century. In 1916 using Einstein's general theory of relativity a German physicist named Karl Schwarzschild calculated that any mass can become a black hole if it were compressed tightly enough. But it wasn't until 1971 when theory became reality. Astronomers studying the constellation Cygnus discovered the first black hole. 

An untold number of black holes are scattered throughout the universe, Constantly warping space and time altering entire galaxies. And endlessly inspiring both scientists and our collective imagination

Can Gravity Beat Dark Energy?

Although it might not seem obvious when you look at the night sky, but we live in a universe that is expanding faster by the instant. Every day, stars fall over the horizon of what we can see, as the space between us stretches faster than their light can reach us. And we can never know what exists past that horizon. So you might imagine or you might have heard about, a far-off future, where space is stretching faster and faster and where all of the stars and galaxies are over that edge. A future where Earth will be left with a dark, empty sky. But luckily for us, or, at least, for hypothetical future earthlings, that’s not actually the case. Because the universe is expanding but not all of it.

We have known that the universe is expanding since the 1920s, but we only discovered that the expansion is accelerating in the 1990s, thanks to the Hubble Space Telescope. Hubble was the first tool to measure really precise distances to supernovas out near the edge of the observable universe. And it showed us that out there, ancient galaxies and the supernovas in them are zooming away from us faster than anywhere else. In fact, astronomers realized that they were flying away even faster than expected. Which, at first, didn’t make sense.

At the time, we thought the universe was dominated by gravity, which pulls things together. So seeing everything accelerate apart was weird. It would kind of be like if you kicked a ball uphill and saw it speed up instead of coming back down to you. Because of this, scientists concluded that there had to be something else going on, something pushing these galaxies apart. They came to call that thing dark energy. Decades later, dark energy is still really mysterious and there is a lot we don’t understand about it.

One explanation is that it’s a property of empty space. This means that space itself, with no stuff in it at all, has dark energy. And that energy pushes space apart, creating new space, which in turn has dark energy, which pushes space apart, creating new space, which in turn has dark energy, which You get it. If dark energy is a property of space, that also means you can’t dilute it. Its density will always be the same, no matter how much space expands.

Of course, that density is also pretty small. If you borrow Einstein’s “E=mc2” trick and express energy as mass, it is equivalent to about one grain of sand in a space the size of the entire Earth. But if you average that over the whole universe, which is mostly empty space, there is more dark energy than anything else. So it dominates and the universe as a whole expands. That’s why the most ancient galaxies are also moving away faster than before.

It has taken a long time for their light to reach us, so the universe has had more time to stretch. Now, this might all make dark energy seem super strong. After all, it makes up more than two-thirds of all the stuff in the universe and it’s pushing apart entire galaxies. But it is only powerful because there is a lot of it.

Within small spaces, especially those full of planets and stars, dark energy is actually pretty weak. Like, the gravity between the Sun and the Earth or the Earth and the Moon is more than enough to overpower the repulsive dark energy between them. In fact, most of the universe’s mass is concentrated in galaxy clusters and these pockets of matter are completely immune to dark energy. They are simply not expanding. 

It doesn’t mean the expansion is negligible, like how technically your gravity pulls ever-so-slightly on Earth but it is not enough to actually notice. It means that, as far as we know, dark energy is truly not stretching our galaxy at all. This is because it’s not a force like gravity, so it works a little differently.

To understand how, think about pushing on a heavy door. If you push lightly, it won’t open. Push a little harder and it still won’t. But if you push hard enough, once you cross a certain threshold of pushing, it will open. That door is gravity and within a galaxy, there’s just not enough dark energy to push it open. 

In other words, gravity is too strong. So our galaxy will never expand, because if it can’t stretch even a little, then it can’t create more space. And that means the amount of dark energy inside will never grow. Of course, this isn’t something we have been able to directly observe, like by looking at other galaxies. But multiple observations have shown us what dark energy is like and they all suggest this should be true.

Eventually, in the really distant future, fewer and fewer galaxies will be visible from Earth. And in 100 billion years or so deep space will be almost empty. But if Earth were still around by then, which, admittedly, is pretty unlikely, we would still have a beautiful night sky. Even as the universe stretches, the glow of our galaxy will still be overhead and we will have stars, constellations and even a handful of galaxies bound by gravity to ours. All because dark energy just can’t get a foothold around here. Of course, this will only last until the heat death of the universe but that’s another story.

The Big Rip Due To Dark Energy

Even though nobody else will be around to see it, scientists are fascinated by the end of the universe. It is kind of like the Big Bang there's just something so interesting about knowing where your atoms came from and where they are ultimately going to go in billions of years. Right now, there are a few ideas about how everything could end, where everything is spread so thin that activity basically stops.

Except, based on the results from a paper published in Nature Astronomy, that might not actually be true. Instead, there is a chance that everything in existence will eventually be ripped apart. And it would all be thanks to dark energy. Scientists think it makes up about 70% of the stuff in the universe and that it is the reason the expansion of the universe is accelerating. But there is a lot they are still figuring out.

Some of their research into dark energy has involved tools called standard candles. Standard candles are objects or events of known brightness that are used to measure distance in the far-off universe. Essentially, if you know how bright something should be up close, then how bright it actually looks indicates how far away it is.

For decades, the most important standard candle has been a special kind of exploding star called a type a supernova. These events always have the same brightness and in the 1990s, they allowed scientists to discover that the universe’s rate of expansion was accelerating. But what is really important for this recent study is that all the estimates provided by type 1a supernovas also indicate that the density of dark energy is fixed.

There is a lot of math involved, but this fact is a big reason they believe the Big Freeze is most likely. The problem is, you can only see so far with any given candle before it gets too dim and type 1a can’t take us back to the beginning of the universe. Because light can only move so fast, looking deep into space is like looking back in time. And these supernovas only allow us to see what things were like 4.5 billion years or so after the Big Bang.

Admittedly, there are some data sources like one called the Cosmic Microwave Background, that can tell us what things were like around 400 thousand years after the Big Bang. But that Background actually seems to disagree with what supernovas say about the expansion rate, which has had astronomers debating different options for years. There is also been a 4-billion-year gap between the two data sources, so it has been hard to figure out what’s going on.

That’s where last week’s news comes in. In their paper, a pair of astronomers proposed a new kind of standard candle, one that can let us peer back to that sweet spot just 1-2 billion years after the Big Bang. Their idea relies on quasars, rapidly-growing black holes that are among the universe’s brightest objects. Although quasars vary a lot in brightness, the authors claim that the ratio of ultraviolet brightness to X-ray brightness is not only more predictable but also reliable enough to indicate a quasar’s distance.

They point out that, at distances where both type 1a supernovas and quasars are visible, they provide comparable results, too. But the key is, farther from Earth, and further back in time, only quasars are visible. And after looking at some of those super-distant objects, the authors claim to have made a surprising observation: In the first couple billion years after the Big Bang, the growth rate of the universe didn’t match the predictions made by the supernova-based models. Back then, things seemed to be getting bigger more slowly than expected.

That implies that the amount of dark energy driving that expansion hasn’t been constant after all. Instead, it has been increasing over time. It sounds like a wild idea, but it would help explain why there isn’t a perfect match between the expansion rate we see from supernovas and that of Cosmic Microwave Background. So it is not like there is no foundation for it. But still, before they rewrite your Astronomy textbook, it is important to remember two things. One, these results will need a lot of confirmation before they are accepted into the mainstream theory. And two, scientists have effectively no clue what dark energy actually is.

So it is not even worth asking questions like what would be generating more and more of it, because we don’t even know what IT is. But if these results are true, there is one thing we do know, instead of ending in the Big Freeze, the universe would eventually end in the so-called Big Rip, where ever-increasing dark energy tears apart every particle until there’s nothing left and no one to see it. But the assumption is that it’s not such a big deal, because there is no way we would be around by then.

Reference:- Quasars as standard candles
Also Read:- Let's Understand Wormholes

Let's Understand Wormholes

Whether it’s Star Trek, Stargate or Babylon 5 wormholes have been showing up in science fiction for a long time. They are just a super convenient tunnel to another part of the universe, a way for sci-fi writers to send their characters across huge distances in the blink of an eye. And it turns out that they are not just science fiction: wormholes could really exist. But if they do, they are much weirder than anything we could make up.

In physics, a wormhole is known as an Einstein-Rosen bridge. It is named after Albert Einstein and another physicist, Nathan Rosen. They came up with the idea together in 1935 and showed that according to the general theory of relativity, wormholes are a definite possibility. A wormhole acts like a tunnel between two different points in spacetime, which is just the continuum of space and time that makes up the fabric of the universe.

According to general relativity, gravity works by bending spacetime. Planets and Stars act like a weight in the fabric of the universe, creating a curve. It can be kind of hard to picture what spacetime is, let alone what it would mean for it to bend, so physicists often talk about it by using weights on a stretched bedsheet as an analogy. Earth would be like a big bowling ball making a big dip in the sheet and when something gets too close to the planet and it’s pulled in by the gravity, it’s like it’s falling into that dip in the sheet. 

But if spacetime can be curved, it can also be twisted and shaped in other ways, like by connecting two different places with a tunnel. It’s kind of like poking two holes into that bedsheet, folding it over and then stretching the fabric so that the edges of the holes can get together and you just sew them into a tunnel. That’s a wormhole in a bedsheet. But because wormholes don’t seem to violate the laws of physics does not mean that they actually exist; they are just technically possible. And unfortunately, we haven’t yet detected any and we aren’t even sure how they would form.

If wormholes do exist, one reason we might not have spotted them is that they could be hiding behind black holes. A black hole is what happens when there is so much mass squeezed into an object that it ends up with such a strong force of gravity that even light can’t escape its pull. Once you get too close to a black hole, you are toast: there is no escaping from being smashed into oblivion. In the bedsheet model, black holes and wormholes look very similar, they both have a steep falloff that seems to go on forever. Except, with a wormhole, the steep drop actually leads somewhere.

According to general relativity, wormholes could have black holes at each end, meaning that after diving into a black hole on one end, the energy that was once your body could get spewed out somewhere totally different in the universe. Of course, you would not survive that trip. All that would be left is radiation and subatomic particles. Then there are white holes, which are the opposite of black holes: They spew out matters with such force that it would be impossible to enter them. If black holes are infinite weights on a bedsheet, white holes would be like hills: objects pushing up on the bedsheet.

Like wormholes, these are a thing that could exist, the math does check out, we are just not sure how they would form. But we know that if they exist, they could be found at either end of a wormhole, too. So, maybe if there was a black hole at one end of the wormhole and a white hole at the other, we could go in the black hole end and be blasted out the white hole end, Maybe. But you would still probably be crushed by the black hole in the process. Not to mention it would definitely be a one-way trip.

There are a few other problems with wormholes. For one thing, they would probably be dangerous. Sudden unexpected collapse, weird exotic particles, a ton of radiation. In fact, travelling through a wormhole could instantly collapse it, because they would probably be unstable. And then there is the fact that wormholes might not be a shortcut at all. A random wormhole could easily be a longer-than-normal path. Size is also a problem. A real-life wormhole could be too small for us to travel through. Not to mention the travel time, which could be millions or billions of years, making some wormholes pretty useless.

So, that’s a lot of problems. The biggest hope actually comes from how little we know. A lot of this depends on physics that we haven’t quite worked out yet or on facts about our universe’s history and geometry that we just don’t know for sure. Once we have all that figured out, the final barrier would be technology and opportunity. Right now, we definitely don’t know how to make a wormhole and we would have to be super lucky to find one that is useful to us if they exist at all.

So, it’s pretty clear that we won’t be sliding through any wormholes anytime soon. But we know that they could be out there, hiding in some of the most extreme places in the universe. And who knows? Maybe our ideas about wormholes will be totally different in the future. People living just a few hundred years ago couldn’t have even imagined particle accelerators or internet. Until we find one or build one Let's will keep exploring the universe.

Let's Understand Naked Singularities

When people talk about black holes, there is one thing that pretty much always comes up is that Black holes get their name because the infinitely tiny, infinitely dense point in the centre has a gravitational pull so strong that even light can’t escape. The thing is, that might not always be true. For the past half-century — basically, as long as we have known black holes are a thing — astrophysicists have been debating the existence of something that should be a black hole, except it’s neither black nor a hole. They are called naked singularities and if they exist, they will rewrite physics as we know it.

When a star dies, it undergoes a gravitational implosion and starts to collapse in on itself. If the star is massive enough, nothing can stop the collapse and all that matter turns into a single point in space. We call that point a singularity and it has zero volume and basically infinite density. Like with basically everything involving infinity, it’s hard to even imagine what that means. But that’s astrophysics for you things get weird.

A singularity isn’t the same thing as a black hole, but it is what causes the black hole. The term “black hole” refers to everything inside the event horizon, the point where the singularity’s gravitational pull becomes so strong that light can’t escape. It is impossible to see anything inside it from the outside. And if you decided to go inside the event horizon to check out what is going on, you would never get out again. So, sure, for a moment you would be the only person in the universe to actually know what’s happening down there, but you would never be able to tell anyone and you’d be stuck until you died.

In 1965, an astrophysicist named Roger Penrose demonstrated that all black holes must have singularities within them. Makes sense, But he couldn’t prove that all singularities need to have a point-of-no-return event horizon and therefore a black hole surrounding them. In other words, he couldn’t prove that it was impossible for a singularity to be naked. He was pretty sure naked singularities couldn’t exist though, even if he couldn’t mathematically prove it. Four years later, he coined what’s known as the conjecture of cosmic censorship, which basically just says that it’s impossible for a singularity to exist without a black hole around it.

Again, he couldn’t prove it, it was just a conjecture. But it was really hard to imagine how an infinitely dense point could exist without a black hole around it and all these decades later, many astrophysicists still subscribe to cosmic censorship. But not all of them. We have obviously never observed a naked singularity, but that doesn’t mean it’s impossible for them to exist.

This long-running debate actually led to one of many wagers Stephen Hawking has publicly made about astronomical discoveries. In the early 1990s, he bet Caltech Kip Thorne and John Preskill that naked singularities can’t exist. The loser had to, quote “reward the winner with clothing to cover the winner’s nakedness,” which was definitely on-theme. Months later, Hawking actually found mathematical evidence, though, not definitive proof that when a black hole finishes evaporating, it might leave behind a naked singularity.

If the idea of a black hole evaporating sounds super strange well, it is. But it is one of the many quirks of quantum mechanics, which predicts that a pair of particles can spontaneously pop into existence with one on either side of the event horizon. If the one outside has the right trajectory, it will escape off into the universe, leaving the black hole with a teeny tiny little bit less mass. But! Quirks of quantum mechanics didn’t fall within the confines of the bet, so Hawking technically hadn’t lost. 

He had to concede in 1997, though, when computer models found a special case for fine-tuned parameters that would produce a naked singularity from an imploding star. Basically, it’s like trying to balance a sharpened pencil on the pointy end Highly improbable, but not impossible. Hawking made the most of his loss, though — he gave Thorne and Preskill T-shirts featuring a woman in nothing but a towel, along with the words “Nature Abhors a Naked Singularity.”

So, simulations are able to suggest naked singularities might form if conditions are just right, but what about more general cases? Well, researchers have found that if our universe had a different number of dimensions or was shaped differently than it is, then yes — it could form naked singularities. But all this could mean that naked singularities only work on paper, not in practice. 

We are kinda stuck with the universe we have got. If by chance we actually learn of a real naked singularity floating around out there in the cosmos, though, it could change our understanding of the universe. Mainly because we would be able to study something that’s governed by both quantum mechanics (the science of the very small) and general relativity (the science of the very massive). 

As it stands, these two theories work almost perfectly when you are using each of them on their own, but they don’t play well together. When you try to apply them both at the same time, like when something is both super duper massive and super duper tiny — basically, a singularity — they spit out nonsense answers. But being able to directly observe a singularity would give us the data to either unite them or scrap them for a different theory entirely. A unified theory of the universe would do more than just reveal the secrets hiding in black holes.

Right now, anything that happened before 10-43rd seconds after the Big Bang is a big mystery because both quantum mechanics and general relativity would apply to it. That is such a tiny fraction of time that you might think it wouldn’t really matter anyway, but, like, those were the very first moments of our universe. In other words, for being infinitely tiny, naked singularities are a pretty big deal.

How Does Google Maps Works?

One of the most annoying nuisances of the modern world is heading out for something important and then getting stuck in a traffic jam. However, if  You are proactive and plan your journey well ahead of time, situations involving those infuriating traffic jams can, in fact, be avoided.

There are a number of tools that can provide a general idea about traffic conditions in a certain area. Even some radio stations periodically broadcast important traffic updates throughout the day. However, the web-based application that is by far the most popular among all the traffic update tools and services is Google Maps a smartphone application designed by Google.

If you have a smartphone and travel frequently it is almost impossible that you haven't used Google Maps. It is an amazingly powerful app that not only acts as a standard GPS device but also gives you recommendations regarding the quickest routes to reach your chosen destinations. Google Maps uses a very smart algorithm to provide real-time updates about traffic conditions and even makes relevant traffic predictions.

The initial versions of Google Maps relied only on data from traffic sensors and cameras that were installed by government transportation agencies and certain private companies that compiled traffic data for various purposes. These sensors use laser radar or active infrared technology that could detect how fast the overall traffic was moving by observing the general size and speed of automobiles. Initially, Google would obtain this information and then embed it in maps for people to use.

However, that method of determining traffic conditions has become obsolete today Google Maps now uses a more sophisticated, reliable and rather brilliant technique known as crowdsourcing to run the app and feed its users the most recent traffic updates on the go.

Crowdsourcing is a fascinating model to collect information on any subject whether that as traffic conditions reviews about products or even memes. It's a sourcing model where an organization obtains services or goods from a large number of people typically via the internet. For instance, the famous ice cream company Ben & Jerry's conducted a crowdsourcing contest to come up with a new ice cream flavour. Participants were supposed to submit their flavour idea and in return, they would get a prize. Since 2009 Google Maps has utilized crowdsourcing to enhance the accuracy of its traffic updates and predictions.

If you use your smartphone to navigate to different places in a city then you already know that in order to use the navigation feature in Google Maps you need to keep your phone's GPS turned on. In simpler terms, if you want to know about traffic conditions in real time you need to keep your phone's location turned on. When you are driving and your phone's location is turned on it sends bits of data anonymously to Google Maps in this way Google learns how fast your device and by extension your car is moving. The same is true for other cars on the road, their phones are also sending bits of data to the Google database.

The app constantly combines this massive amount of data coming from all the cars on the road, processes it and then sends it back to the same phones in the form of real-time traffic updates. In other words, it's your phone and the phones of your fellow drivers that feed Google Maps with the data it needs to provide live traffic updates.

The interesting thing about this technique is that if you don't want Google to gather location data from your phone you can always opt out of the service by simply toggling your phone's location to off. However, if you do that you also won't be able to view live traffic updates in Google Maps. All in all Google Maps is an incredibly useful and intelligent app that not only takes you places but also helps ensure that you don't spend half your life stuck in traffic jams.

Let's Understand White Holes

White holes are almost definitely not a real thing that can be found in nature. In theory, white holes are black holes that are going backwards. In theory. A black hole, as you know, is a giant object that sucks stuff into a singularity - a single point of infinite density - from which there is no escape. So a white hole would be an object that expels matter from a singularity and you would never be able to enter it. White holes only exist in math.

But in 2006, we saw an explosion of light out in deep space that we can't explain any other way. It is even weirder than it sounds. In reality, a white hole would violate the second law of thermodynamics. Which says that the amount of entropy in the universe can only stay the same or increase. It can never decrease.

Entropy is often described as disorder, but it's more like a measure of how many different states that particles in a system can be in at any given moment. Like, if you have a piano and you throw it in a woodchipper, you have increased the entropy of the piano. Because a pile of chopped-up piano splinters can be in lots and lots of different configurations while still being a pile of splinters. But these piano splinters can really only be in one, very specific state in order to be a piano.

So, black holes are great at increasing entropy! They are the universe's woodchippers: shredding entire stars into pulp and leaving only a whiff of radiation. But you can't load your pile of piano splinters into the woodchipper and run the thing backwards to get a piano again. That would decrease entropy, which is not allowed. And if white holes existed, that's essentially what they would do.

So why does anyone think white holes might exist in the first place? Well, they were first proposed as a kind of mathematical oddity, because of Einstein’s theories of relativity. One of the many endearing quirks of relativity is that it doesn't care whether you play time backward or forward. If time can go in one direction, it can just as easily go in the other. So if black holes are a thing, then white holes (which are black holes played backward) can also be a thing.

But just because relativity says time can go in both directions, in practice it pretty much sticks to one, as we all know. So even if a white hole did somehow occur, it would be incredibly unstable. Because the universe does not like it when you break the laws of physics. So a real white hole would probably only last for a few seconds before it collapsed in on itself to become a black hole.

Which brings us back to the explosion we saw in 2006. Detected by NASA’s Swift satellite on June 14, it was a huge gamma-ray burst: the highest-energy type of explosion possible, a million trillion times more energetic than the Sun and it lasted for102 seconds. Scientists believe that gamma-ray bursts only last that long during supernovas.
But this one, labelled GRB 060614, didn't have a supernova to go with it. As far as we can tell, it was an explosion of white-hot light that came from nowhere and then vanished. And while white holes remain incredibly, stupendously, ridiculously unlikely that's pretty much exactly what we think one would look like.

Some physicists have offered other explanations for what it might have been -- like a shock wave from neutron star torn apart by a black hole, or maybe two neutron stars colliding. But events like these only release energy for two seconds at most -- not a minute and a half.

So, White holes in nature are as impossible as a thing can be, while still being technically possible. And until we see another explosion like the one in 2006 that we could hopefully learn more from, we will just have to wait and wonder.

What Would Happen If You Detonate A Nuclear Bomb In Space?

Detonating a nuclear bomb seems like a risky business in general, but in the early 1960s, the US and the Soviet Union were busy trying to figure out what would happen if you set one off in space? The answer turned out to be something they didn't really expect. A nuclear blast could cause a high-altitude electromagnetic pulse or EMP, a powerful man-made burst of electromagnetic energy that could basically wipe out communications here on Earth.

It was a whole new way to use the bomb and they kind of discovered it by accident. It all started in 1958 when the US launched its first satellite Explorer 1. NASA scientist James Van Allen equipped it with a Geiger counter, because he wanted to measure radiation at different altitudes, a project he had already been working on using balloons. 

The readings that came back were strange. Radiation levels seemed to increase with altitude, then suddenly dropped to 0, then increase and then suddenly dropped to 0 again. More testing showed that readings that looked like 0 were actually because the radiation levels were so high that the detector couldn't handle it. But that spring Van Allen realized he made a new discovery: that there were at least two belts around the planet between 1,000 and 60,000 kilometres up with extra high concentrations of charged particles like electrons and protons.

Today we call these belts the Van Allen belts and we know that they are mostly made of particles from solar wind and cosmic rays, held in place by Earth's magnetic field. We also know that depending on solar activity there can be more than two of them.

In May of that year, Van Allen presented his discovery at a press conference at the National Academy in Washington DC. Later that day, the US military asked for his help detonating nuclear weapons in the Van Allen belts. US military officials suspected the Soviets were doing high-altitude nuclear tests. And at the time nobody really knew how a high-altitude explosion would differ from one here on Earth. Newly discovered Van Allen Belts added a whole new element because nuclear blasts release lots of charged particles and here with these two huge bands of more charged particles.

The US was worried that interference from the Van Allen belts might hide incoming missiles or that they could somehow be used to steer a blast. So they decided to learn more about how atomic bombs behaved at high altitudes by detonating a bunch of them. During those tests they ended up measuring electric signals so high they thought it was a fluke caused by other flaws in the instruments they were using. But they had to wait a while to figure out what was really happening, because later that year the USSR called for a ban on high-altitude nuclear testing and the US agreed. 

Then in 1961, the USSR started testing their own nukes at high altitudes anyway and the US quickly continued their own, including a test known as Starfish Prime. Starfish Prime was humanity's first hydrogen bomb detonated at a high altitude. It detonated 400 kilometres above a point near its launch from Johnston Island in the Pacific Ocean. It was also the biggest bomb ever set off in space, 100 times more powerful than the Hiroshima bomb and with a blast equal to about 1.4 million tons of TNT.

But with so little air around it, it didn't make a fireball. Instead, the charged particles zooming away from Starfish Prime caused a huge Aurora that could be seen for thousands of kilometres around Johnston Island. And then, burglar alarms started going off in Hawaii more than a thousand kilometres away. 27 rockets followed Starfish Prime to gather data and even they weren't equipped to measure what happened. What the US learned was that the oddly high measurement from earlier tests weren't glitches. 

High-altitude nuclear explosions are just very different. In the near vacuum up there, the energy from nuclear blast sends out lots of free electrons. Those electrons create a brief but extremely powerful electromagnetic pulse: an EMP. Starfish Prime's EMP was so strong, it affected the flow of electricity on Earth thousands of kilometres from Johnston Island, causing blackouts and electrical malfunctions in Hawaii and disabling at least six satellites. But that was in a relatively isolated area. 

Today an EMP could be used to disable an entire country. The US commission to study EMPs in 2008 estimated that an EMP attack could kill 90% of the US population within 12 months since so much of the way we live depends on satellites and the electrical grid. The US military ran a few more tests after Starfish Prime, but they kept things a lot smaller and the data from those tests is still classified. 

Only a year later the USSR proposed another moratorium on high-altitude nukes: the Limited Test Ban Treaty of 1963, and we haven't set off any nukes in space since then. So in the end humanity was probably right to be worried about the consequences of detonating nuclear bombs in space, but mainly because they accidentally stumbled upon a way to make the aftermath of the bomb even worse.

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