It’s 4 am on a mid-August morning in the northern California wilderness. During a brief overnight storm, lightning strikes the top of a hill, ignites some dry underbrush, and starts a wildfire. It isn’t until 6am as the sun rises that someone notices the fire—a hiker camping an overlooking hill. As soon as the hiker’s 911 call is received by the emergency dispatch center they contact Cal Fire—the agency responsible for wildfire protection and management in California. By 6:30, they call the Redding, California-based smokejumpers. They are one of the most elite firefighting squads in the United States. There are only 400 smokejumpers in the USand 40 of those are based here in Redding, California. 

They’re essentially the rapid response team for wildfires. Within 15 minutes of receiving the call, these smokejumpers are in their plane and taking off. It takes just 20 minutes to fly the 50 miles to the fire site where they find a suitable tree-free landing spot, jump, deploy their parachutes and land. The plane then circles back to parachute down boxes of equipment. Smokejumpers carry with them enough supplies to last 72 hours completely self-supported—food, water, shelter, safety equipment, and fire fighting tools. They follow the ridgeline and make their way to the fire. Now, this is a small team and they need to decide how to prioritize what they do. With the fire already had grown to 15 acres the team knows they’re unlikely to stop it on their own, backups are already on the way, so their priority is to slow it down as much as possible. There are four major factors that affect how fast a fire moves: how much fuel there is, how wet the fuel is, the wind direction, and the slope. The two factors that the team can immediately gauge that affect where the fire will move the fastest are the wind direction and slope. In this case, the wind is coming from the north and they know that to the south-west is an upward slope. Fire moves faster uphill than it does downhill since fire burns upwards so these smokejumpers know that this is likely the fire’s fastest-moving front. While trees do burn, the primary source of fuel that a wildfire uses to move is the dry brush and deadwood on the forest floor so the biggest technique used to stop forest fires is to create what’s called a fireline. These are essentially a gap where they remove all fuel—plants both dead and alive—so that there’s nothing for the fire to continue burning. The smokejumpers use a mix of chainsaws and other hand tools to do this work but sometimes fire lines are pre-built. In this case, there’s a road at the top of the uphill section which will help slow or stop the fire so they can direct their efforts elsewhere. They use the road as their anchor point—a cleared section that the fire likely won’t cross where they start building their fireline so the fire can’t outflank them. Throughout this construction process, the smokejumpers need to be sure that they can escape in case the winds shift or the fire picks up speed. Wildfires can move exceptionally fast—up to 7 miles per hour in forests which is faster than humans are often able to make their way through dense trees. In grasslands, fires can move up to 14 miles per hour so firefighters have to be extra cautious. For this reason, firefighters rarely put themselves directly in front of the fire’s moving front—they’ll either be far ahead or to the side. In the case of this fire as they’re building this first fire line they’re close to a road which acts as an easy exit point but, just in case, all smokejumpers carry fire shelters. These compact, lightweight shelters won't survive direct flames for too long, but they do greatly increase a firefighter’s chance of survival in case they can’t escape the path of the fire. After a little over an hour of work, 

the smokejumpers complete a continuous fire line from the road to a stream. Streams, while less secure than roads, also help stop or slow down a fire by acting as a fire line. To the south-east of the fire there’s also a small road that connects to another stream meaning there are at least rudimentary firelines on three sides of the fire. It’s at this time when backups arrive byroad. The added manpower allows for much faster action. The immediate focus goes to strengthening the southeastern fire line—currently just a stream. At the closest the fire’s less than 100 feet from the stream and the stream is itself in a valley so it’s too risky to work directly behind the stream, there’s just no good escape route, so the new arrivals get to work on a redundant fire line 100 feet behind the stream. By 10 am the fire has further grown and the team knows that the worst is still to come. Fires spread most rapidly between 10am and sunset due to the daytime heat and wind. By 11am the fire has reached the road and part of the fire line which means that some of those that we're building the fire-line are re-allocated to make sure that the fire-line holds—extinguishing any flames that may jump the road. By noon the fire lines are holding and, while the fire’s size is growing, it’s at a manageable pace so there’s reasonable hope that it can be suppressed before expanding to an uncontrollable size. At 1pm, though, conditions change. The wind starts blowing harder towards the south-west and, as trees burn on the north side of the road, the wind pushes embers over the road which ignite underbrush on the other side and now the entire focus of the firefighting efforts change. You see, the point of fighting wildfires is not actually to put them out, it’s to control them. While the number of wildfires has increased due to humans they’re actually a very natural phenomenon. What’s making wildfires worse is humans stopping them. Many forests survive wildfire through trees having heat-resistant bark and other evolutionary adaptations. These fire-resistant forests relied on having wildfires at a consistent interval every few decades to clear out the forest floor of dead plants and to kill invasive species. Nowadays, though, as humans suppress fires a forest might only see a wildfire every 50 years instead of 25, for example, meaning that there’s twice as much fuel and so the fire burns faster, larger, and more intensely. It was only until recent years that the research revealing this was widely accepted so the goals of firefighting shifted from stopping wildfires completely to controlling them. In some places, being a firefighter actually means starting fires. Fire management agencies will conduct controlled burns in order to reduce the risk of an uncontrollable fire and to increase the health of a forest. While forests can survive wildfires, humans can not so most agencies will let fires burn in a controlled fashion up until the moment they risk damaging property or threatening human life. This fire that jumped the road just did exactly that. At the bottom of this slope is a town andthe fire is now headed in that direction with no preexisting features to stop it. That means that all measures must be taken to aggressively stop the fire’s expansion to the west. That means it’s time to bring out the big guns—it’s time to attack the fire from above. Planes and helicopters are some of the most effective tools used to fight wildfires. They can quickly and accurately drop huge amounts of water or fire retardant. The decision to use aerial firefighting does not come lightly as it’s both hugely expensive and using an aircraft on one fire means it can't be used on another. Their use needs to be prioritized to the most dangerous fires. There’s also a decision to be made on what the aircraft is going to drop—water or flame retardant. Water is cheap and, with some aircraft designs, can be reloaded near the fire without landing at an airport. Water is only effective at extinguishing flames, though. Flame retardant, on the other hand, can be used to stop flames from starting. It can essentially create a fire line ahead of the fire’s spread as it will stop a line of the forest from burning. The main issues, though, are that flame retardant can only be loaded at an airport and it’s very expensive. A gallon of Phos-Chek, the most commonly used brand of flame retardant, costs $3. That’s about the same as a gallon of milk at the grocery store but these aircraft use thousands of gallons of it for each drop. The world’s largest firefighting aircraft, the 747 supertankers, for example, carries 19,600 gallons of flame retardant meaning that what it uses in one drop costs nearly $60,000. Of course, there’s a reason agencies hire this plane, it creates a 3-mile long fire line almost instantly, but it comes at a steep price. For this fire, using such an expensive tool would be overkill. In this case, they’ll use a helicopter with a bucket attached. The bucket is filled with water from a nearby lake then the helicopter flies over to the fire and drops it. With only 5 miles to the lake, the helicopter is able to make a drop about every 5-10 minutes and, while it works on stopping the spread on one side hand crews work on building a fire line on the other. 

The area that the helicopter extinguishes essentially acts as its own fire line as fire can’t burn what’s already burned. This work continues for the next few hours—it's vital to not let anything to the south-west of the road burn out of control. By 4pm the outbreak is managed and attention can be directed back to the largest section of the fire. As the afternoon wears on some crews get back to lengthening the eastern fire line, others begin constructing a western fire line, andthe helicopter works on slowing the advancement to the north. By the time the sun begins to set around 8, all sides of the fire have at least some element of control so that during the night and in the coming days the fire can continue to burn in a controlled fashion until there’s nothing left to burn. This mission was a success but the reality is that this is not a real fire. Real fires rarely end this well. Real fires don’t act so predictably because real fires can’t be predicted. Real fires are a menace that can grow to the size of small countries and can burn for months. During summer and fall, there are often more than 100 large forest fires burning around the US at any given time and thousands more around the world. No firefighting effort is exactly like another but these are the primary techniques used by those who work every day to protect life and property from one of nature’s most dangerous phenomenons. Whether you’re fighting forest fires or running a business the tools you use are crucially important. In both cases, they directly affect how well you do your job and, while chainsaws, axes, and shovels are some of the most important tools in firefighting. 

Some people would argue the most important year in the history of soup was 1962, when Andy Warhol released his soup-er soupy pop art. But I think soup’s best year came to a decade earlier, in 1952, when a scientist named Stanley Miller first cooked up the primordial soup. Miller’s experiment took some simple chemicals, like those found on early Earth, bubbled them up through a tube, zapped them with electricity, and after a few days, floating in this soup, he found amino acids–the building blocks of proteins, and one of the essential ingredients for life. This idea–that life’s origins could be found in a puddle of chemicals–is an old one. In the 1920s, two different scientists theorized about life arising from what they called a “prebiotic soup”. And this soupy speculation even goes back(unsurprisingly) to Charles Darwin, who in 1871 wondered if life may have formed from chemicals “…in some warm little pond…” What made Miller’s experiment so special was it gave us proof: regular non-life stuff could become cool life stuff super-easily. But… everything “living” we see today, even the most basic bacteria, is so complex, built of such intricate machinery, it's impossible to imagine they just popped into existence out of some soup. That’s because they didn’t. We’re going to go on a journey in search of the origin of life, and along the way, there will be a few forks in the road, maybe a couple speedbumps, and we’re going to need help from a couple friends. We’ll come to see that Miller’s primordial soup isn’t exactly how this story began. But the FIRST question we should ask isn't life started, it’s when. Life on Earth couldn’t exist before Earth existed, and it formed around four and a half billion years ago, at the dawn of the HadeanEra/Eon. Soon after that, another planet collided with the young Earth melted the entire crust, and created the moon in the process. After the crust cooled, there was even some liquid water… at least for a little while. Because for the next couple hundred million years, Earth was showered with hundreds of massive space rocks.

    The oceans boiled away, the crust melted again, and Earth was basically no place for life… until things settled down about 4 billion years ago, at the dawn of the Archean Eon. This is the earliest possible time that life could have started on Earth, the beginning of what we call the habitability boundary. And fossil and chemical evidence tell us that early microbes existed by 3.7 billion years ago, what’s known as the biosignature boundary.

At some moment in here, non-life became life: we call this abiogenesis. Now, I don’t have a time machine. As far as I know, no one does. Therefore we can’t go back and find that exact moment. But if we could, what would we look for? This brings us to the next big question on this journey… what is life? You’d think biology would have a good definition of life, the thing it studies. But as a biologist, I can tell you this is much harder than it sounds. In one chapter of biologist JBS Haldane’s1949 book What Is Life? he literally writes “I am not going to answer this question.” Life is a board game, a delicious breakfast cereal, and a highway? According to the dictionary, it’s the time between birth and death. But none of these definitions really help us. I think we might be asking the wrong question because life isn’t a thing that things have, life is what living things do. In school, many people learn a checklist for the characteristics a thing must have to be “alive”: MRS GREN. But this list came from looking at life as we know it today. Life at the very beginning was probably much simpler. A physicist, Erwin Schrödinger, looked at all these things that life does and saw something only a physicist would see: According to the second law of thermodynamics,.

But inside of living cells, there’s a huge amount of order and complexity. In 1944, Schrödinger defined life as a struggle against entropy– the persistent resistance of decay, the preservation of DISequilibrium. Since then we're learned a lot more about entropy, and it may be that the rise of complexity is as inevitable as its decay. That sounds pretty good. Life creates these little closed systems where it works to keep things nice and ordered. But this definition still leaves out one important thing: Living things evolve. Inside the very first living things must have been molecules–chains of atoms–that carried information–instructions for building things or codes for doing stuff. Those molecules must have copied and made more of themselves, some a little different than the others. And a few of those codes and instructions must have been better at doing whatever they did, so they made even more of themselves. What we’re describing is evolution by natural selection, Darwin’s famous idea, and for life to move forward, it must have been there from the beginning. Life is a product of evolution. With all this in mind, maybe we’re finally able to come up with a better definition: Life began the moment that molecules of information started to reproduce and evolve by natural selection. And now that we have a definition we can make some rules for what something has to do to be “alive”.

1. A living thing must work to avoid decay and disorder

2. To do that, a living thing has to create a closed system or be made of cells

3. They have some molecule that can carry information about how to build cell machinery

4. This information must evolve by natural selection sounds pretty good, but rules are one thing.

The ultimate question is how would this actually happen? Let’s take these rules one by one. What would it require for these things to arise? And–most importantly–how likely are each of these steps based on what we know from good ‘ol real, actual, hard science?! Today, no matter where we look on the tree of life, most cell machinery is made of protein– chains of folded amino acids. When modern cells make proteins, they copy genes from DNA into RNA and then use that RNA as a blueprint for making the proteins. We call this universal pathway the central dogma of biology, because it sounds really cool, and because it's something that all life shares. But there’s a paradox hidden in here–a puzzle. It’s a chicken and egg problem! DNA needs proteins to make more of itself. And cells need DNA and the instructions it holds to make proteins. So which came first? We can solve this paradox in a pretty simple way. Just get rid of DNA and protein in the earliest days of life, and let RNA do everything. RNA is the molecular cousin of DNA. It contains the same four-letter alphabet code as DNA, only T is replaced by a similar molecule, U. And instead of two strings in a helix, RNA is usually found in just one string. RNA is special because, in addition to carrying information in that 4-letter code, it can fold up into interesting shapes and actually do stuff. The same way that protein enzymes can do all kinds of chemical reactions, RNA enzymes–called ribozymes–can work life’s machinery too. It’s now thought that life began in an RNA world. Before DNA became a more permanent form of storage, different RNA chains could have carried information and been the machines for all of life’s important chemistry. Unfortunately, the RNA-only world went extinct more than 3 billion years ago, but we can make these RNA enzymes today. Scientists have constructed ribozymes that can copy themselves, just like DNA gets copied. And those copies occasionally have errors or changes, so RNA can evolve too.

If you need more proof you can find it right inside your cells. The ribosome, the massive structure that stitches amino acids into protein, is mostly RNA. We also find nucleotides, the single molecular units of RNA, inside a bunch of other molecules our cells need for metabolism. This all makes sense only if the earliest days of living chemistry were dominated by RNA. And it solves our chicken and egg problem.

The RNA world takes care of two of our four rules:

A molecule that can carry information (3) and that can evolve (4). To find answers for the other two, we need to ask one more question: Where did life begin? There’s been a lot of theories about where life came from, but they boil down to these: Either life arose on Earth, or life arose somewhere else and was brought here. It’s well-known that space is full of the chemical building blocks of life, from amino acids to DNA and RNA letters... ...buried inside meteorites like this one that fell on Australia in 1969. It shows the chemistry that makes biological molecules can happen pretty much anywhere. But the idea that life was delivered to Earth on space rocks, which goes by the awesome name panspermia… well there’s just no proof it ever happened, and it doesn’t really explain the origin of life anyway. It just moves it somewhere else. Life probably started here. No… zoom out a little. We know early Earth had plenty of chemical ingredients, but the problem with that old idea of primordial soup is that soup can't anything on its own–those chemicals can’t react without outside energy. We get a hint of where this primordial energy came from by looking (again) at our own cells. Instead of lightning, or heat energy, our cells pile up a bunch of hydrogen ions (protons) on one side of a wall, let ‘em flow downhill, and use this as the water wheel to push on cellular machinery (and make things like ATPin the mitochondria) We burn food to keep our hydrogen pump going, but the first life forms wouldn’t have been able to do this, because tacos hadn’t been invented yet. Instead, they would have needed some natural source, and they could have found it at the bottom of the ocean.

Deep-sea hydrothermal vents are covered in microscopic little pockets, which could have served as molds for the first cells. Molecules with one oily water-hating end and one water-loving end have a neat habit of forming bubbles and sheets all on their own and there were plenty of these in the chemical soup near deep-sea vents, ready to give rise to the first cell membranes. These vents also create natural streams of hydrogen ions near those little pockets in the rock. Imagine an early life form sitting there, wrapped in its little membrane bubble, with a free source of energy flowing by, powering all the work it takes to create ordered life and resist entropy. But this would have been the absolute simplest form that life could take. For this life form to become a life that looks like what we know today, a lot more stuff had to happen: it had to switch from storing its genetic information in RNA and started using DNA. Instead of using RNA and ribozymes to run all its cellular machinery, it had to start stitching amino acids into proteins. This opened up new possibilities for making and storing energy that let early life become free-living and more complex. One of these complex life forms is the ancestor of everything alive today, the last universal common ancestor, or LUCA. This is the end of our journey, searching for the origin of life on Earth. A lot has happened since. This story is based on things we’ve actually seen, not just on what’s possible. We’ve figured out when life could have started. We’ve come up with rules for what life is. We’ve found clues inside our own cells that explain how the first life satisfied these rules, and where that life might have started. The only question we haven’t answered is why, but that’s not really a question for science, is it? There are still quite a few gaps to fill in this story, and if you’re looking for a nice, neat answer for how life started, you're probably not going to find it. Life is just a thing that happens. It’s still happening today, and it will evolve and continue as long as there’s a place it can happen. Darwin didn’t know it when he wondered about that warm little pond, full of chemicals, giving rise to life, but his theory of how things change and adapt turned out to be so powerful it encompasses life not just in its endless forms, but also in its first ones. Stay curious. Wow. That was a LOT. This is probably the deepest story I've ever done.

 

    The thing is that space distances are seriously long. That's why traveling takes way more time than you'd like to spend the time on the road! For example, a space probe launched in 1977 (Voyager 1), that was traveling out of the Solar System at a speed of 40,000 miles per/hour. If my spacecraft moving at the same speed, it would take me a whole 77,000 years to get to the nearest star! I mean, really? It would also take me more than a billion years to cross the Milky Way galaxy! But luckily, the Invincible is much faster than that. Also, I almost forgot to introduce my companion- sorry, Liam! You see, Liam is a robot with AI (you know, Artificial Intelligence). That's why I have high hopes for him: I'll have someone to talk to during the flight, and he can help me if things get really tough! And now, let the journey begin! Here we go!…..3,2,1, blast off! Wow, the Earth is growing smaller and smaller by the second. It seems like no time has passed, but the spacecraft is already 200 miles above the surface of our planet. Since it's daytime, I can clearly see theGreat Lakes shining in the sun! And oh boy, I've just spotted something moving to the left of my ship! Could it be?... Right! It's the International Space Station! Did you know that the station is the most expensive single object in the world? Huh, no wonder, with a price tag of $100 billion! This money would buy you 250 Boeing 747s or two Louvre's with all the paintings and artwork inside! From my spacecraft, the ISS looks pretty big, but I shouldn’t be surprised, since the length of the station is over 350 feet, which is more than the length of a football field. But I don't have time to linger, a black hole is calling for me. Now, I'm about 1,300 miles over the surface of the planet, and I start to spot satellites here and there. I've read that among satellites, there are low and high flyers. And while the lowest flying ones move approximately1,250 miles away from Earth (which is the length of 4 and a half Grand Canyons), the highest reach 22,000 miles into space (which almost equals the Earth's circumference, measuring about 25,000 miles).

By the way, few people know that satellites travel at a blinding speed, from 7,000 to 18,000 miles per hour! Also, the higher a satellite is, the slower it moves, relatively speaking. For example, the weather-tracking GOES system of satellites orbits Earth once a day at a distance of 22,000 miles above your head and reaches a maximum speed of 7,000 miles per hour. Meanwhile, the ISS, in low earth orbit, zoom sat over 17,000 miles per hour. Well, the satellites are being left behind, and my spacecraft is already taking Liam and me up toward the Moon, about 240,000 miles away from Earth. That's the same distance you would go if you went around our planet ten times in a row! From here, Earth looks like a small, bright blue ball hanging in the middle of nowhere. And you know what else? From my spacecraft, I can clearly see that the Moon isn't a perfect sphere! It's shaped more like... hmm... yeah, like an egg! Wow! Anyway, bye-bye, Moon, we're heading somewhere even further! I see Mars, Jupiter, Saturn, and Neptune passing by in all their glory. And look, there's Pluto, who used to be a planet but was later demoted. From here, Earth looks like a small star that getting fainter and fainter as I'm moving further away. But wait, what's that? Some object is approaching me at a high speed, could it be... TESLA?! Whoa! That was close - the thing just avoided a collision at the last moment, and everything happened too fast to see it clearly. But I'm pretty sure what I just saw was a Telsa... Right now, I'm already really, really far from Earth, like 100 astronomical units away. The thing is that space distances are so vast, you can't even calculate them in miles. That's why scientists use the term "astronomic unit," which equals 93 million miles – the distance from the sun to Earth. That means I'm 9.3 billion miles away from our planet! But w-w-what's happening? Why is my spaceship shaking and rocking so much?! Ah, I see! We're entering the termination shock, the place where solar winds coming from the Sun travel at a speed of 250 miles per second and collide with the material that makes up the galaxy's background. There! We made it through unscathed, but there another trial ahead - the Oort Cloud.

That means two things: first - we're on the outskirts of the Solar System; and second - we'll have to get through a cloud of icy objects orbiting the Sun at a distance of a 100,000 astronomic units! In other words, it's 1.87 light-years away from our star. Phew! It must be my lucky day since we got through the Oort Cloud with just a couple of scratches on the spacecraft's skin. And voila! - we're heading out of the SolarSystem just one-tenth of a light-year later. By the way, if you were trying to reach this point by car, the trip would take you more than 19 million years. And even if you piloted one of the fastest spacecraft that exist nowadays, NASA's New Horizons, you would still need 37,000 years to complete the journey! Bring a big lunch. Alright, we’ve left the borders of the SolarSystem, and now, I'm sitting in my spaceship cabin, watching comets and asteroids pass by. Time to think about my destination. In the center of every galaxy, there’s a supermassive black hole.

a. supermassive black hole

b. Stellar black hole

For example, one is sitting right at the heart of our Milky Way galaxy, about 27,000 light-years away from Earth. But even my ship wouldn't be able to get that far before my 100th birthday. That's why my destination is the stellar black hole, nearest to Earth and much smaller in size, but no less mysterious! It's V616 Monocerotis (aka V616 Mon), located3,000 light-years away, and weighing the same as about 9 to 13 of our Suns! A black hole is an eerie place where those laws of physics we studied at school stop working. If a massive star runs out of its star fuel, it becomes super-dense and buckles under its own weight, collapsing inward and bringing space-time along. As a result, the gravitational field of this new thing gets so strong that nothing can escape it, not even light! Right now, we're approaching the black hole, and very soon, I'll send Liam to explore it from the inside! I won't go further than the horizon, aka the point of no return, and you can probably guess why, right? Once an object crosses this invisible line, it can't turn back, even if it's changed its mind. Anyway, Liam says he's ready to start his journey. There he goes, bravely plunging toward the black hole while I'm recording everything that's happening to him. He’s accelerating; it looks like he’s contorting and stretching, as if I'm looking through a huge magnifying glass. Interestingly, the closer to the horizon is, the more slowly he seems to move. He’s trying to send me encoded light messages, like we agreed to in advance, but the light waves stretch to redder and lower frequencies, "I'm Ok, I m Ok..." What’s happening? Liam just froze, as if a gigantic finger has pressed a pause button, and now, some force is stretching him thinner and thinner! Ah, I've read about this phenomenon - it's the infamous spaghettification, which happens in a super-strong non-homogenous gravitational field! The black hole's gravity force is stronger at his feet than at his head; that's why he’s getting stretched out like a piece of spaghetti! Also, the sensors inform me that Liam is getting hotter and hotter... and then…. nothing! He just disappeared, and I can't see him anymore. But since I did my research before the trip, I know that Liam is in a state of free-fall now, and feels no more stretching, scalding radiation, or gravity. Unfortunately, the connection is lost, and he can't tell me anything about the inside of the black hole. Hmm, this is a moment I didn’t think through well enough. Anyway, I hope you're Ok out there, my friend! And I think I'll head home to get ready for my next space trip! What about you? Do you think I should go all the way and explore this the black hole myself next time? Let me know down in the comments! If you learned something new today, then share it with a friend.

    

              A violent and sudden inflation from darkness to our current bright night sky A mighty event that's at the birth of our universe. Not just a tiny moment in time but a still ongoing event of creation. As of today, we will see the expansion of our universe that was once created by the Big Bang. In this two-part special we will dive into the moment this dramatic event took place and will theorize what was before the creation of our known universe. It's all about before and after the Big Bang. Our universe contains the most dramatic and beautiful things you can imagine. We have billions of stars, planets, galaxies, and dust clouds in all sizes and different matters. From the bright Sun to black holes it all came together in one epic event. Some things aren't even possible for us humans to put into perspective 13.8 billion years ago, the birth of our universe took place. An event we call the Big Bang. It's an explanation of how our universe was created. Before we go on this violent journey, we must understand what a singularity is. This is an event in which property is infinite just like a black hole. 

       The more gravity you have in a location the more it bends space. When you bend space you also bend the distance between points A and B. Bending points A and B would also bend time. If there is so much gravity in one place very strange things start to happen Gravity is crushing everything into such a dense state this is called infinite gravity. Gravity is pulling everything into an infinite density. You now have a singularity. A mind-bending event in which the current laws of physics do not apply anymore to this region of space Our universe was once a very small singularity before it stretched over 13.8 billion years to the universe we can now observe. The Big Bang was not an explosion but an event in which space expanded out of an infinite singularity To this current day our known universe is still stretching and when Hubble figured out that other galaxies formed by the Big Bang were moving away from our galaxy, the galaxies that are further away from us move faster than the ones that are close to us. It means that the universe is still expanding. We know everything around our solar system moves away. So at one point, everything had to be very very close together. But let's go back to the beginning Because everything was extremely close together, it was a very hot place. At the start of this Big Bang, we have had a dramatic moment which we call Planck time. This is 10 million trillion trillion trillion trillionth of a second At this moment the temperature reached100 a million trillion degrees Within a second the universe expanded very fast. After that second the temperature cooled down to 100 billion degrees. After just one second all the manner created by this event were protons and neutrons. It only took about 13 seconds before the temperature dropped further to 3 billion degrees We fast forward to 700,000 years later. An important moment in which the temperature dropped enough to form the first atoms; the building block for ordinary matter. Atoms can merge together to create molecules that form almost anything around us. But how do we know all of this? It's not like we had first-row seat tickets to watch this unimaginable event happen it's like a water drop that falls in the water. We study the ripples created in the water to understand where this ripple originated from scientists study everything around us to understand at which point this event took place. An important part of the understanding of the Big Bang is the speed in which galaxies are moving. Some galaxies move at unbelievably high speeds of at least100,000 kilometers a second. 

When you look far away in the universe there's so much more you can see. You can even go back in time. Humans made highly advanced telescopes that can see very far. When the universe was created by theBig Bang this sudden expansion created an enormous amount of light. Scatteringthrough the universe. Because our universe is stretching the light is stretched into microwaves. With a microwave telescope, we are able to observe ancient light all the way back to the beginning of our universe. Light plays a vital role in understanding when everything we know was created.We have these telescopes so we can look at space billions of light-years away. Because it takes so long for light to reach us, we are looking into the past and are seeing that dust clouds created by the Big Bang. As if it just happened We have a lot of tools to make complex mathematical equations that explain the burning question of how our universe was created. But why aren't we able to see the exact start of the Big Bang. Just like the clouds we are able to see 13 billion light-years away. Let's use our imagination. You're standing on Earth but there is no light, it's completely dark, no way for your eyes to adjust. The Sun is the start of the universe. But the Sun also has no light You are literally observing the start of our universe in the darkness. At the creation of our universe, there was no light. Light literally didn't exist yet, so you will never be able to see the start of our universe. It's hidden behind the clouds of darkness. It's still a difficult thing to realize, it all started from nothing because what is before nothing? If you identify nothing isn't it then automatically something? In the next episode, we will theorize what happens before the Big Bang. Feel free to subscribe so you don't miss the next part. Thank you for watching we have given you a small look into this subject. We might have missed something. We might have gotten something wrong. Let us know what your thoughts are. 

Your time is very precious and as the tickling of the clock goes on, it realizes you that you have spent one more second of your life and it won't come back again. We all have seen the time machines in science fiction movies that can travel us into our future. But is it possible in our real-life?? Well, keep watching Gateway to knowledge to know is time travel possible for humans?? Well, to begin with, you must know that the time travel is of two types going back in our time and going forward in time. So let's discuss the first type that can we travel back in our time?? we know that traveling back is impossible. Even sending information/data back in time is very difficult to imagine this is because it can change things that have already happened which should be impossible. Time traveling is a confusing idea for most people that's because when we think of the time we think about it, as going in a straight line with one thing happening after another. If we travel back in time and change something that happened before, change the order of that lines. This would mean breaking a rule called the "casualty". Casualty is the rule saying that a cause happens before an effect, and it is one of the unbreakable rules of the universe breaking this rule would have nasty consequences for the universe and all of us. Experts think that because the universe has this rule, traveling to the past must be impossible otherwise, the rule would have broken all the time. So, now comes the second question that can we go forward in our time?? Well technically, we are already traveling forward in time because time is passing every second and we are traveling one second into the future. But this happens to everyone so it's not real-time traveling, right?? you might not believe, different time rates can be felt by two different peaple. Time passes differently for someone who is moving fast as compared to someone who is standing still.

This is actually a very complicated idea that is known as the "time dilation". Let's consider, someone is flying from Sydney to Melbourne will feel time passes more quickly than who is waiting for them at the airport without moving. So, why don't we notice this difference?? It's because you have to be moving much much faster than an airplane. Before you start to notice this time dilation, even if you flew all the way around the world, the time would only feel a billionth of a second, different to someone who stayed at home The only way scientists even know about the time dilation is because of amazingly accurate experiments that have measured it. Unfortunately, this still can't help us to time travel. If you feel around the world for more than 4 million years, people on the ground would only have experience one more second than you. So, if it's all about speed then how fast can we go to travel time?? If you could go fast enough for long enough hundreds of minutes could slip by on your journey, which means that you would feel like you were traveling into the future. Unfortunately, the speed enough to the close to the speed of light, which is the fastest speed anything can go. Light travels at about 1 billion kilometers an hour and that's very, very fast.  The fastest human-made things Nasa's Parker Solar Probe which is a spaceship sent to the sun in August2018. but as fast as, it is it's only 0.064percent as fast as the speed of light. So the light is more than 1000 times faster. All of this means that if humans want to visit the future we have got a long long way to go. OKAY, so we can't time travel but we still have some hope that we can actually do it, because the technology is advancing day by day and we are very much hope that we humans can move as fast as the speed of flight.