If the universe as we know it started with the Big Bang, will it also have an end? And if it’s going to end someday - how? Discover the four main ideas about how the universe might end, and find out which one has the most evidence supporting it. With host Athena Brensberger, dive into our universe's very distant future in this episode of What the Physics?!

If the universe as we know it started with the Big Bang, will it also have an end? And if it’s going to end someday - how? Here are four leading ideas.

4 Ways the Universe Could End

It’s an age-old question: Do aliens exist? And what are the odds we’ll make contact? A famous mathematical equation, known as the Drake Equation, helps scientists estimate the odds of finding intelligent alien civilizations, but new discoveries and unknown factors could change everything.

The Drake Equation helps scientists estimate the odds of finding intelligent alien civilizations.

Do Aliens Exist? This Famous Equation Offers a Clue

Imagine taking an elevator to space. Or blasting off in a nuclear rocket. That might sound like science fiction, but scientists are racing to develop new, more efficient methods of space travel - and some pretty wild ideas are on the table. Discover the rocket-less future of space travel and the quest to make it happen.

Space elevators? Nuclear rockets? The future of space travel could look radically different.

The Rocket-Less Future of Space Travel

The Gordon and Betty Moore Foundation

What the Physics?!, a YouTube series from NOVA, explores mind-blowing ideas and questions from the world of physics like space travel via elevator, the odds that aliens exist, and the ultimate fate of the universe!

What the Physics?!

Dream Hacking: Decisions, Addictions, and Sleep

Watch the first-ever video documenting this live two-way dream communication.
Have you ever felt drawn toward choices without knowing why? Or, as seen in the movie “Inception,” have you ever felt like you’ve woken up with a decision that’s already been made for you?Neuroscience is beginning to demystify such feelings. Our agency and decisions, it turns out, can be measurably influenced by events that evade the conscious part of our brains. We’ll see three groundbreaking experiments that illustrate that influences we are unaware of in our waking life, during dreamless sleep, or even in our dreams can impact our memory and behavior.Published on February 18, 2021, in the journal Current Biology, an international team of scientists have found a bridge to the dream world by showing that it’s possible to have a direct dialogue with someone in their dream—and NOVA’s Greg Kestin (host of “What the Physics?!”) was given exclusive access.The scientific context and potential effect of this team’s work are built up in the film through two related groundbreaking experiments. These experiments also show how scientists can influence your decisions, desires, and habits without you being aware. 
Dream Hacking: Decisions, Addictions, and SleepPublished: February 18, 2021Karen: They&#x27;re communicating to us from a dream. Greg: You&#x27;re about to see three groundbreaking experiments... Laura: When they woke up, they were actually less inclined to smoke. Greg: ...that reveal, not only how hidden parts of your mind can control your decisions... Nick: Seven times it happened? I thought it happened twice. Greg: ...but also how scientists can manipulate your preferences, desires, and habits without you even being aware. So how do they do it? Inception: Inception. Greg: Like in the movie Inception, they do it by sneaking ideas into people’s brains and by manipulating dreams. What you’re about to see may make you question what or who really controls your decisions.Before getting to dream control, do you even control your decisions when you’re awake? Moran Cerf is a former hacker. And these days he hacks the brain. As a neuroscientist, he&#x27;s attempting to implant an idea, a preference into these volunteers’ minds without them being aware it&#x27;s happening. And while he does it, he monitors their brain with a device called an electroencephalogram or EEG. Moran: The experiment is going to ask you to make a repeated decision. Each trial is going to have the following stages. First, you&#x27;re going to see the choice, two options. Then you&#x27;re gonna make a choice, left or right. And then we&#x27;re going to ask you to explain to us. Christina: She looks really intelligent. Diara: The other one seemed a little bit more sad. Nick: She looks like somebody who was fun and friendly. Greg: After the participant makes several decisions, Cerf does something a little tricky. Pay close attention. The subject chooses the woman with the lighter hair on the right side. But five seconds later, when the card flips over, he&#x27;s presented with the picture of the woman that was on the left.Nick: I like this person&#x27;s dimples. Greg: Not only does he not remember that that wasn&#x27;t the person he originally picked, a phenomenon called Choice Blindness, but he also comes up with a reason for why he did pick that person. So, could this actually change who he prefers in the future?Moran: Part two, almost the same, just without the need to explain. Greg: Now, when faced with the identical decision, will his preference be the same or different?This time he chose the woman on the left. It appears that, without him being aware, his preference has successfully been changed.The EEG gives Cerf a clue to what&#x27;s happening in the subjects&#x27; brains.Moran: So the way we think about it is that there are, in your brain, cells that code value or that code preferences. So imagine you have to choose between steak and a fish and you&#x27;re about to make a choice. The fish cells on the left side of your brain are starting to fire, indicating, &quot;we want fish.&quot; At the same time, the cells on the right are starting to fire, indicating, &quot;we want the steak.&quot; And there is kind of a battle between those two. And at some point there&#x27;s enough majority from one side, rather than the other. Then information gets sent to you, the conscious you, then says &quot;Fish,&quot; not knowing that under the hood there was an entire battle going on. Greg: This unconscious battle impacts how your brain actually decides between different foods, different videos, different faces. But by explaining a false choice, that creates a false memory that influences the unconscious battle in one direction versus the other. Every once in a while, they&#x27;d actually catch the switch. Nick: Thought I chose the other one. Diara: I think I chose the other one. Christina: Thought I chose the other image. Greg: But most of the time this switch does go unnoticed.Diara: Probably more the eyes on this one. Greg: And it doesn&#x27;t just work with faces.Moran: It works to an extent with choices that we think are not just arbitrary and small, but ones that define who we all like political choices. So, you can&#x27;t easily take a Democrat and make it a Republican or vise-versa. But you can take definitely a person who says that they&#x27;re going say 9 on how liberal they are, and in a small manipulation, make them shift to scoring 6. Greg: But for someone to dramatically change your habits or even addictions, your memories may need to be even more vulnerable to manipulation.Moran: We can actually find moments in your life where your guards are down. One of those moments is when we&#x27;re sleeping. Greg: A study was done by a research group at Israel&#x27;s Weizmann Institute. They took habitual smokers and asked them to track how much they smoked over a particular week. Then at the end of that week, they asked the smokers to come into the lab for a night of sleep. Then over the following week, they tracked how much they smoked again. It turned out that over that following week, they smoked significantly less. So, what happened to the smokers when they slept in the lab? It all comes down to what they smelled during the night.Laura Shanahan is a neuroscientist at Northwestern University who does similar research studying sleep and odors.Laura: Sleep is really important for consolidating our memories. What if we could actually go in and manipulate that process? The sense of smell is often a really underappreciated sense. Greg: So, when the smokers in this study slept in the lab, they were equipped with an odor delivery system and an EEG to track what stage of sleep they were in.Laura: When they fell asleep researchers presented two different smells to their noses repetitively: cigarette smoke and the smell of rotten eggs. They had no idea that they had smelled the smells during sleep ... Greg: Without their awareness their sleeping brains, by some mysterious process, associated cigarette smell with the rotten egg smell, and as a result... Laura: They were less inclined to smoke cigarettes for the following week. Greg: Laura was intrigued by research like the Israeli study, and wanted to understand the mechanism that makes such a powerful transformation, during sleep, possible. Laura: What we wanted to understand was what happens in your brain when you smell an odor during sleep. Greg: She designed a study wherein the subjects played a simple memory game involving pictures of animals, buildings, faces and tools.Laura: They were learning the locations of these pictures on a four by four grid. Greg: Before their memories of those locations were tested, they were hooked up to a machine that delivers odors to their noses.Laura: Most of us have a particular scent that evokes a very specific memory. In our study, we decided to take advantage of this system. So, for instance, they might learn that cedar odor belonged with pictures of animals and that rose odor was associated with pictures of buildings. Greg: So the cedar smell goes with animals, the scent of roses, buildings. Then the participants went to sleep in the MRI machine. During deep sleep, Shanahan presented them with cedar odor, but not rose odor. From the MRI, she could see just how much the cedar odor reactivated, in their brains, images of animals.   Now it was time for the participants to wake up and take the memory test. Would that unremembered mental replay of animals during sleep improve their memories of the animal pictures? Laura: So people had a better memory for those locations that were reactivated by odors during sleep.Greg: Without knowing why, they were better at remembering the locations of the animal pictures compared to the building locations. Similarly, in the Israeli study, the subjects&#x27; memories of smoking and rotten eggs were presumably retriggered, reducing their desire to smoke. What&#x27;s strange, though, is that these memory manipulations, which can profoundly impact our behavior, only work if the subject is sleeping . So, what if you could actually control the images that appeared in your sleeping mind? Professor Ken Paller and Karen Konkoly are conducting some of the first experiments in real-time two-way dream communication , and the first step is training their subjects to access their own dreams. Ken: So lucid dreams have been known for a long time. There is a special category of dreams where the dreamer understands that they&#x27;re dreaming. Once you understand that you&#x27;re dreaming, there&#x27;s the possibility of controlling what is happening in the dream. So lucid dreamers enjoy doing this. They love to go and fly. Greg: Before training the subject to lucid dream, Karen places an EEG on her.Karen: We can use EEG to see what stage of sleep somebody is in and we can also use it to see where they&#x27;re looking with their eyes. Ken: In their dream, their body is paralyzed. So they&#x27;re not moving. But the eyes are an exception. Greg: Knowing where they&#x27;re looking is important because the subjects aren&#x27;t asked to, say fly in their dreams, which they might only be able to describe after waking up, but rather to demonstrate control of their dreams by having a real-time conversation with researchers with their eyes, from within the dream.Ken: One way to have a two-way conversation would be to ask them to solve little math problems. And we&#x27;ve already agreed on a code for those where one is moving left-right wants to is moving twice, three, moving three times and so forth. Greg: Now, the first step in training is to teach the participant various eye signals. Karen: If you become lucid in a dream, then you want to look all the way to your left ear, all the way to the right, all the way left, all the way to the right, as fast as you can. Greg: Now the participant goes into the sleep room, which is equipped with a red light and a speaker so that Karen can communicate with them. As they get ready to sleep. Karen starts the second step of training by flashing a faint light or playing a faint sound over the speaker, followed by directions.Karen: As you notice the signal, bring your attention to your thoughts and notice where your mind has wandered. Greg: She directs them to practice what&#x27;s called a reality check. Karen: Reality check is when you ask yourself very sincerely, am I awake or am I dreaming? Greg: In the movie Inception, unique objects called totems were used to distinguish reality from dreams. But Karen and Ken have some tricks anyone, including you, can use to check if they’re in a dream.Karen: If you study your hands a lot of times in dreams, they become really strange. Ken: The storyline just is bizarre sometimes, and that&#x27;s a hint that you&#x27;re dreaming and actually not awake. Karen: If you read something, look away, and then read it again, a lot of times in a dream, the words will change.Karen: The best reality check is just to become really critically aware of your environment. Karen: Remain lucid, critically aware, and notice how aspects of this experience are in any way different from your normal waking experience. Greg: After about 20 minutes of similar training, the participant begins to fall asleep. Karen: When their eyes start moving and they&#x27;re completely paralyzed, you know that they&#x27;re in REM sleep. Greg: As the subject enters REM sleep, the phase of sleep where narrative dreams occur, Karen again softly plays that violin sound or flashes the dim red light, hoping that the subject will become aware of the signal from within the dream. Michelle: I was looking at my old house. I saw the light cue; that flashed kind of like intertwined with my dream.Karen: We&#x27;re waiting for her to give a left, right, left, right eye signal after one of the light cues that we give her, or one of the violin sounds. In lucid dreaming, it&#x27;s certainly true, wherever you&#x27;re looking in the dream corresponds to where your eyes are looking in your waking body. Michelle: I acknowledge that there was a light cue. I was also dreaming at the same time. Karen: So now we know, okay, our participant’s having a lucid dream. So, we quietly celebrate and then we try to communicate by giving them an easy math problem. Karen: Two plus one. Michelle: So then I incorporated by envisioning the math problem on the house number plate. Greg: While this is happening, Karen carefully monitors the EEG to make sure the subject is still asleep. One reliable indication that the subject is sleeping is a reduction of electrical signals coming from the chin, confirming that the body is still paralyzed.Michelle: I would transform that into the math problem. Greg: She now signals from her dream, the number three with her eyes.Karen: It seems like we&#x27;ve successfully communicated, so we&#x27;re gonna wake her up and see what she remembers. Greg: This live dream communication shows that we can control the images that occur to our, malleable, sleeping minds. This opens the door to training ourselves, in our dreams, to make better choices. And it may even help us solve difficult problems in our lives.Ken: We&#x27;re planning to do the same experiments with problem solving. If you&#x27;re struggling with something, you might decide that your lucid dream would be a good chance to revisit that problem and see if you can come up with a more creative answer to that problem.  Greg: So, the unconscious forces from your sleeping or wake mind, can really impact your habits and decisions. But really understanding these forces could change even more than that...About 400 years ago, when we began to accept that we on the Earth weren’t at the center of the solar system , a revolution in understanding our universe began.Moran: Our coming years will allow us to explore not just the conscious us, but the other parts, if we begin to understand that we are not the center of our own universe. In understanding that, we will not only uncover a lot of things about how we think, how we decide, how emotions work, how dreams work, how memories work, but we&#x27;ll understand essentially how all of those become what we call &quot;me.&quot;

Watch the first-ever video documenting this live two-way dream communication.

What is the Coriolis Effect?

The spinning of Earth means we don&#x27;t always see straight paths as straight.
Anytime you&#x27;re rotating—whether it&#x27;s on a playground toy or your home planet—objects moving in straight lines will appear to curve. This bizarre phenomenon affects many things, from the paths of missiles to the formation of hurricanes. Find out more in this episode of <a href="http://youtube.com/whatthephysics">What the Physics?!</a>
What is the Coriolis Effect?Published September 25, 2018Greg Kestin: What&#x27;s going on here? Every time I throw the ball straight, it seems to bend to the side. No matter what I throw, no matter how straight I throw it, the ball seems to be curving. Maybe it has something to do with this: That whole time I was spinning, which is why it looks like I&#x27;m about to puke.That curve is created by the Coriolis effect. You may have heard that it makes water in the bathtub spiral down the drain a certain way or that it determines the way a toilet flushes. That&#x27;s actually wrong. Those are not caused by the Coriolis effect. But the Coriolis effect does create hurricanes and is the reason why Jupiter has a Great Red Spot.So, what is the Coriolis effect? Well, it&#x27;s what happens when objects moving in a straight line appear to curve because you are rotating. And it affects all kinds of things. It bends the paths of missiles and sniper shots. Its effects are only really noticeable over large distances; that&#x27;s why it has nothing to do with flushing toilets. But how does it work, and how does it create hurricanes?Right now, it seems like the ball&#x27;s curving. But let&#x27;s take a look at what&#x27;s really happening.My friends and I put together this little experiment using a sort of spinning seesaw. Here, the camera&#x27;s standing still; it&#x27;s just hanging from the ceiling. And watch what happens. From the moment the ball leaves my hand, it&#x27;s just going straight. Let&#x27;s watch that again, frame by frame. Keep your eye on the ball. You can see that it travels in a perfectly straight line.But what if you&#x27;re spinning with the seesaw? Look at what happens when you rotate the footage so the seesaw stays sideways and everything moves around it? Now let&#x27;s follow the path of the ball again but from this new perspective. The trajectory looks completely different. Now let&#x27;s watch this one frame by frame.From this rotating perspective, it totally looks like the ball is curving. That&#x27;s crazy because you already saw that exact same throw. Watch it again on the left. The ball is going straight, but on the right, when you&#x27;re rotating with the seesaw, the ball really looks like it&#x27;s curving.You might be thinking, why should I care? I don&#x27;t spend a lot of time on a spinning seesaw or on a merry-go-round. But you kind of are on a merry-go-round.Have you ever seen someone in a movie making fine adjustments on their gun? Well, one effect they&#x27;re correcting for is the Coriolis effect. The longest sniper shot, which was over 3,000 yards, would have had to correct for a one-foot deviation due to the Coriolis effect.So, how does the Coriolis effect create hurricanes?Hurricanes form when air rushes from all directions into a low-pressure region. So, imagine there&#x27;s a low-pressure region between the two of us. Air is going to rush toward the center. Let&#x27;s see what that looks like from space, from our camera that&#x27;s hanging from the ceiling. It&#x27;s not spinning, so the air--or in this case, the balls--are clearly going in a straight line.But if you&#x27;re rotating with the Earth, or with the seesaw, you&#x27;ll see the air bend to the right. In the northern hemisphere, this creates hurricanes with counterclockwise spirals. In the southern hemisphere it does the opposite; it creates hurricanes with clockwise spirals.This storm on Jupiter, which is actually bigger than the Earth itself, all began because of the Coriolis effect. So, when you&#x27;re in a rotating frame, the Coriolis effect seems to exert a very real force on objects. But there is no force; what you observe is just a result of your perspective.And you might be wondering, if this is simply a product of your frame of reference, then could other forces, like gravity or electromagnetism, also just be products of your frame of reference? Of where we live in the universe? Or in the multiverse?For more on that, check out our video &quot;Do We Live in the Multiverse?&quot; There are talking fish.And if you want to find out when new episodes come, click subscribe.

The spinning of Earth means we don&#x27;t always see straight paths as straight.

How to Slow Down Time

In different but similar ways, both your brain and the laws of physics can slow down time.
Under the right circumstances, your brain can trick you into experiencing some time intervals as longer than others. But under other circumstances, time itself really does slow down. The two phenomena—psychological and physical—are more similar than you might think. Find out more in this episode of <a href="http://youtube.com/whatthephysics">What the Physics?!</a>
How to Slow Down TimePublished August 23, 2018Greg Kestin: You&#x27;re about to see a deer appear in three clearings. Watch that again.Does it take more time for the deer to go from A to B or from B to C? Here it is a couple more times.Most people see the deer take longer to go from B to C. But in reality, it takes the exact same amount of time to go from A to B and B to C.This illusion slows down your perception of time—and it is just in your head—but you can actually use the same concept to understand how time, in reality, can actually slow down.When you see the deer appear at A, then B, your brain registers how fast the deer is going, and then, subconsciously, calculates: When the deer travels three times farther, from B to C, it should take about three times as long. Or at least, it should take longer.But this calculation is what fools your brain. It assumes the deer is moving at approximately a constant speed. And that assumption makes you expect a longer time interval from B to C. That overrides your actual observation.So, believing the deer keeps about a constant speed changed your perception of time. Of course, that was a trick that your mind played on you. But real time dilation does exist—and exists because there is one speed in nature which is constant: the speed of light.Light will always travel at 186,000 miles per second or, rather, one foot every nanosecond. This means you can theoretically use light to measure time by building a kind of light clock.Imagine a light beam bouncing back and forth between two mirrors separated by six inches. One bounce up and down is one foot and therefore one nanosecond. This is where it gets strange.Let&#x27;s say you&#x27;re holding your light clock on the side of some train tracks and your friend Karen has a light clock in the passing train. She&#x27;s zooming sideways, so the light from her clock doesn&#x27;t just go straight up and down like it does with your clock. It goes up and down, but the train is also pulling it this way, so it ends up following these diagonal lines. And those diagonal lines are longer than your vertical lines. In other words, one tick of Karen&#x27;s clock covers a longer distance than one tick of your clock.But light travels at a constant speed in both. And if light travels the same speed for a longer distance, it must take more time. So, one tick of Karen&#x27;s clock is slower than one tick of your clock. Karen&#x27;s clock—and Karen&#x27;s breathing and Karen&#x27;s heart and everything in the train—is slowed down. Time moves more slowly for anything in motion. And for things moving really fast, like, say, satellites, this time slows down by several microseconds per day.GPS clocks have to factor in this time dilation effect, or else they wouldn&#x27;t sync up with the clocks on Earth.So, what&#x27;s really cool is that the real stretching of time happens because the speed of light is constant, just like that apparent stretching of time happens because your brain thinks the speed of the deer is constant.If you want to learn more about time dilation, check out our video on how to use time dilation to travel millions of light-years to another galaxy—all in your lifetime.

In different but similar ways, both your brain and the laws of physics can slow down time.

What Is What the Physics?!

What the Physics?! is about the physics in you, of you, and around you.
What the Physics?! is about the physics in you, the physics of you, and the physics around you. If you’ve been enjoying our videos, <a href="http://youtube.com/whatthephysics">find us on YouTube</a> to catch up on old episodes or subscribe to find out about new ones.
What Is What the Physics?!Published August 1, 2018Greg Kestin: What I have here is just olive oil, a torch, the universe, bubble wrap.The oil has calmed all the waves.These were magnets.All because of your perspective.It feels a little light. I&#x27;m Greg and What the Physics?!If you want to see more What the Physics?!, please subscribe.

What the Physics?! is about the physics in you, of you, and around you.

Physics Is Erasing Your Memory

Thanks to physics, no memory can last forever.
You might store your precious memories in diary passages or in photos backed up on a hard drive. But thanks to physics, no memory can last forever—not in a diary, not in a hard drive, not even in your brain. If you could live forever, you would eventually forget everything. Find out why in this episode of <a href="http://youtube.com/whatthephysics">What the Physics?!</a>
Physics Is Erasing Your MemoryPublished July 25, 2018Greg Kestin: So, I have a torch and some neodymium magnets. Let&#x27;s see what happens when I heat them up.So, these were magnets...until we heated them up—and they forgot. The same phenomenon that made the magnets forget that they were magnets ensures that no memory is permanent and even you will forget everything you ever knew.Oh, by the way, did you turn off the oven? It&#x27;s a simple yes or no. I know, sometimes you can&#x27;t remember. Maybe what you need is a little switch—something where it says, &quot;Yes, I turned it off&quot; or &quot;No, it&#x27;s still on.&quot; &#x27;Cause that would be a simple way to remember one single bit of information, whether it&#x27;s good-bad, yes-no, or one-zero. But what if you wanted to store many pieces of information, like the information that&#x27;s encoding this video, which is 1 gigabyte? That&#x27;s 8 billion ones or zeros. Eight billion little switches would be the size of Manhattan if you put them right next to each other.Luckily, we store information in a smaller kind of switch. So, in a hard drive, we have small magnets whose north poles point up for one or down for zero. There are actually several trillion magnetic switches in here. But why aren&#x27;t hard drives even smaller? It&#x27;s because the microscopic world is a dance party, with molecules bumping and jiggling. Here are some pollen grains in water—and scientists thought the pollen was actually alive, until Einstein proved that it was just water molecules that were hitting it and making the pollen grain dance.And just like the water, the molecules in the hard drive are bouncing and jiggling and they&#x27;re making those little magnets bounce too. And that&#x27;s sort of a problem because they could eventually jiggle and flip over. And if that happens, then we lose the information that that single magnetic switch was holding. And that&#x27;s what happened when I heated the magnets with the blowtorch.Each of those magnetic balls is made of many small magnets, which are all pointing in the same direction—until you heat it and the microscopic bumping increases, flipping over some of those magnets and de-magnetizing the ball. If you tried to make a hard drive with even smaller magnets than we currently use, then that flipping over could occur at room temperature fairly quickly and they could lose their information in a matter of days.Current hard drives can only hold information for about 200 years. So, what does this have to do with information in your brain? Your memories?When you remember something, a particular sequence of neurons is triggered. An electrical signal travels down one neuron over a small gap to the next neuron, and that signal continues along the neurons until all the neurons that are related to that one memory have been triggered.So, that little space between neurons? That&#x27;s called a synapse and that controls whether or not the signal can travel from one firing neuron to its neighbor. And that signal can only cross if there are enough of a certain kind of molecule at that first neuron. Those molecules are called neurotransmitters.The problem is that, over time, microscopic bumping can push those neurotransmitters out of place, preventing the signal to go from one neuron to the next. So, if you&#x27;re trying to remember something but one link in that chain of neurons is missing, you won&#x27;t be able to get to the rest of the memory.On a day-to-day basis, there are other mechanisms that can cause you to forget. Things like similar memories interfering with each other and the presence of a different kind of neurotransmitter that actually makes you forget instead of remember. But if we could live much longer, or if you went into cryogenic sleep for centuries, then every memory you have would become dislodged because all of this bumping would knock neurotransmitters out of place. It&#x27;s all because of this little microscopic party.And, like any party, it makes you forget. And the cool thing is...that...um...I forget.By the way, the loss of data from bumping doesn&#x27;t just affect brains and computers. It affects words that you write down, because the ink can actually be bumped out of place. And it affects DNA, which is why—I&#x27;m so sorry to say this—finding dinosaur DNA is actually impossible.Oh, I remembered: subscribe. That&#x27;s what it is. Yes, thank you. Subscribe.

Thanks to physics, no memory can last forever.

What Does an Atom Look Like?

It’s pretty different from the atom you saw in your textbooks.
You’ve probably seen drawings of atoms everywhere from science textbooks to the logo for The Big Bang Theory. But the truth is much stranger than most of those images let on. So what does an atom really look like? Find out in this episode of <a href="https://www.youtube.com/whatthephysics">What the Physics?!</a>
What Does an Atom Look Like?Published June 14, 2018Greg Kestin: So, what does an atom actually look like? Because it doesn&#x27;t look like this.If you google pictures of an atom, you&#x27;ll see a lot of pictures like that. And even here at NOVA, we get it wrong, too. All of these pictures are wrong. But if you could make the atom a trillion times bigger than it is, then the nucleus would look a little more like this and the atom itself would look a little more like this.What does it mean to actually see something? I mean, am I seeing this cantaloupe? Because the cantaloupe isn&#x27;t touching my eye. What does touch my eye are photons: particles of light. A photon leaves a lamp; it bounces off the cantaloupe into my eye. And then another photon hits at a different angle and then also enters my eye.That same thing happens with billions of photons. And if I retrace all those photons, then I can see the cantaloupe. And it&#x27;s weird to say, but that&#x27;s what seeing is: It&#x27;s sharing a bunch of photons with...a cantaloupe.We can sort of &quot;see&quot; a hydrogen atom using a similar method. Take a few high-energy photons and shoot them at a hydrogen atom. The photons don&#x27;t bounce off like with the cantaloupe. What they do is they knock one of the electrons from the hydrogen atom out and it flies, not to an eye, but to a detector, say, here. If you do it again with a second hydrogen atom, the electron would land, say, here. If you do it again and again and again, what you&#x27;ll eventually get is this cloud. Tracing those electrons back to where they came from, you&#x27;d find all the places you&#x27;re likely to find the electron within the hydrogen atom if you were to look for it. This cloud of probabilities is beautifully different for different atoms.OK, so the standard picture of the atom should, maybe, look a little more like this. But what about the nucleus? Because in this picture, relatively, it&#x27;s too big. If the electron cloud were the size of a football field, then the nucleus would be the size of a grain of sand. 99.9999999999999% of an atom is actually empty space.Physicists don&#x27;t think of the nucleus as a cluster of protons and neutrons like a cluster of grapes. They actually learn about it in a similar way as the electron. They actually shoot electrons into the nucleus and protons and neutrons come out the other side. And what they learn is that the nucleus is much more like a droplet, a region where you could find the proton or neutron. It&#x27;s sort of like the electron cloud, except much more dense. And they don&#x27;t yet fully understand what&#x27;s going on inside the nucleus. But they do know that the nucleus comes in cool different shapes for different nuclei.While our standard picture of the atom is a pretty good schematic, to be a little more accurate, we might want to imagine the atom more like a cloud with a tiny droplet in the middle.For much more, check out NOVA Wonders &quot;What&#x27;s the Universe Made of?&quot; And if you want to see more &quot;What the Physics?!&quot; please subscribe. I can&#x27;t believe I caught it...and then dropped it.

It’s pretty different from the atom you saw in your textbooks.

What Does Dark Energy Look Like?

The mysterious substance ripping our universe apart.
In 1998, astronomers planned to discover whether the universe would expand forever or eventually collapse under its own gravity. What they found instead shattered every expectation: something was overpowering the pull of gravity and pushing the universe apart. They called it dark energy. But what is this invisible substance that makes up 70% of our universe? Find out in this episode of <a href="http://www.youtube.com/whatthephysics">What the Physics?!</a>
What Does Dark Energy Look Like?Published June 6, 2018Greg Kestin: What if you threw a baseball up in the air and it never stopped? And then, not only did it defy gravity, it started racing away faster and faster with nothing propelling it. That&#x27;s exactly how astronomers felt in 1998, except, instead of a ball, they found the entire universe was racing apart faster and faster by the instant. So, why would the universe do that?Our best theory is that there&#x27;s something invisible all around you—and even though you&#x27;ve never seen it, it makes up 70% of the universe. It&#x27;s called dark energy.So, 20 years ago, by looking at supernovae, astronomers noticed that the universe wasn&#x27;t just expanding outward—it was actually accelerating faster and faster outward. Not even the explosion of the Big Bang could have set this in motion. And they began to think maybe space itself is expanding.But saying space just is special and expands is kind of random. It&#x27;s like having magnets and seeing them attract and just saying, &quot;OK, magnets attract,&quot; and not worrying about electromagnetism or the fields involved.Now, remember, in Einstein&#x27;s view, spacetime is basically this mesh that just sits there unless energy or matter bends it. And you might have seen videos or images of the bending of that spacetime mesh that causes things to attract. But maybe there&#x27;s a special kind of substance, something invisible and undetectable that pushes the spacetime mesh apart.OK: Imagine that space is full of bubbles that repel each other. And whenever there&#x27;s enough space for a new bubble to form, it does. And that bubble repels all the other bubbles. And then bubbles keep popping into existence, pushing each other apart, and pushing space with it. So, space and time probably isn&#x27;t made of bubbles, but on really small scales, you actually do have particles popping in and out of existence. They&#x27;re called virtual particles, and they live for a very short time before they annihilate each other.So maybe the energy of these particles is what&#x27;s causing the universe to expand. But if you calculate the amount of pushing from all the virtual particles that exist in the standard model of particle physics, you get too much pushing. You actually get a trillion trillion trillion trillion trillion trillion trillion trillion trillion times too much pushing. So, our current quantum theories of particle physics can&#x27;t explain observations of dark energy. And some people think we just need to add something onto those quantum theories—something like supersymmetry. But other people think that we actually need to change our theory of gravity—change general relativity so, say, space itself expands without worrying about these particles.Either way, dark energy is even hard to imagine. Even in our shows here at NOVA, we show some beautiful things, but they&#x27;re not what dark energy would look like. If you make dark energy, say, green, so you could see it, it would actually look like this. It has the same density everywhere. And if it started to expand, it would actually do this. You see it expanding? Dark energy doesn&#x27;t even get diluted because it&#x27;s embedded in space. As space expands, you get more space, but you get more dark energy with it, and it looks the same.For now, all we know is that the bigger the universe gets, the faster it flies apart. And one day, the distance between our Milky Way and the neighboring galaxies will be growing faster than the speed of light. When that happens, even our best telescopes won&#x27;t be able to see those galaxies. I say, let&#x27;s get to know our neighbors while we still can.

The mysterious substance ripping our universe apart.

Brand: What the Physics?!

Hero Feature