Transcription
What's in the middle of the galaxy? Because it looks like a a light.
>> There's a black hole. Look, this in this picture, the density of stars is way higher in the middle of the galaxy than out here.
>> Why?
>> We're figuring that out. We think in the formation scenario of the galaxy that most of the mass is near the center and it gets thinner as it comes out. And so we're going to have the most stars where the most mass is that you start with. So it's not it's not a surprise that the middles of these things have the most stars because they have the most mass and in the exact middle in the center is a super massive black hole which we've measured to be there. In fact a Nobel Prize was given for that measurement.
>> Can you explain what a black hole is like on the 12?
>> Oh yeah. You know it first you got to respect black holes. Give them don't ever diss a black hole because you will lose. So, we're here on Earth and uh the old adage, what goes up must come down. You've heard that. I would learn by the time I was nine that that's just false. No, by the time I was 10 because I was 10 years old cuz that's how old I am. We walked on the moon and then we left part, you know, rocket parts on the moon.
>> Those are never coming back to Earth.
>> So, there are things that went up that never came back. Okay. All right. Well, what started the adage, though? Well, if you take something and toss it, it actually slows down, comes to a stop, and then speeds up and comes down again. It's captured by Earth's gravity. Turns out there is a speed with which I can throw this so that it never comes back. Let's get there. If I throw this a little faster with more energy, it goes higher before it comes back. Right? How about even faster? Even faster. Gets higher and higher and higher and higher and higher. You can calculate using physics and gravity equations. There's a speed with which this will go so high up it'll reach infinity. If it reach infinity, it's not coming back. That's called the escape velocity for Earth. How fast is that? It's really fast. really fast. Uh 7 miles per second.
>> If I throw this at 7 miles per second, it'll reach the edge of the universe and never come back to Earth. Suppose Earth had more gravity than it currently does. Does it make sense that that escape velocity would be greater than 7 m/s?
>> Mhm.
>> If Earth's gravity were stronger, it might be 10 miles per second, 100 miles/s. Keep up this exercise, you'll reach a point where your object has an escape velocity that equals the speed of light. The moment it achieves that, light cannot escape. It's not moving fast enough. And if light can't get out, it's black. If you fall in, you are never coming out because you can't ever reach the speed of light. There's no greater definition of a hole than that. Hence, black hole. By the way, Einstein could have predicted them, but he was it was too weird for him to go there with with his equations. We would learn about black holes mathematically in the 1960s, make our first discovery of one in the 1970s, a famous uh source of X-ray energy called Signis X1. And and then now there's they're common and we've even discovered them in the centers of galaxies that have super like a million times the mass of the sun. Monstrous black holes dining on anything that comes close.
>> Just things that come close.
>> Yeah. It's not going to reach out. So, if the sun were to become a black hole now,
>> it won't reach out and grab us and suck us in.
>> It'll have the same gravity
>> as a black hole as it does as a as a star.
>> But it's if you go close.
>> Yeah. If you get Now, you can get really close to it and then you're not coming out.
>> Is there a certain distance where
>> It turns out there is there's a distance around every black hole. I I think it's called the ergosphere. It's got a it's got a a name where there are no stable orbits around it. If you get closer than that, you you will fall in no matter what. Whereas beyond it, you can maintain a stable orbit and look at black holes from a distance, right?
>> And where'd you go if you get sucked in?
>> Well, are you crushed or you
>> Well, depends how big the black hole is.
>> Small black holes just That's all she wrote. Okay.
>> This one.
>> Oh, that one you just you'll fall in. And then where do I go? I'm just collapsed.
>> Well, there are books. I have one on my shelf and I've even read it. Uh it's a graduate textbook that describes the mathematics of space and time on the other side of a black hole. And it shows that a whole new spaceime opens up in front of you.
>> What?
>> Inside the black hole, the whole universe. The math shows that given the general theory of relativity which gives us black holes in the first place. If you follow the math, you get a whole spaceime that opens up inside the black hole. And as you fall in, your time changes. So time ticks more slowly for you relative to the universe. It's called time dilation. And so as you look out in the universe, the universe will unfold faster and faster and faster. And you will see the entire future history of the universe unfold as you descend into the black hole.
>> When you say descend, cuz I I thought of it as like, you know, if you go close to black hole, you're going to be crushed into a small mass.
>> Well, I didn't get to that part yet. I'm describing what happens to space and time as you descend through what's called the event horizon. That's the region out of which you don't escape. That's the functional size we give to black holes. How big is its event horizon? you cross over within that volume. That's where the escape velocity is greater than the speed of light and you're not coming out. So it has taken the fabric of space and time and folded it back on itself. So there's no pathway you can take to get out of a black hole. You're in there forever. And for the small black holes, here's an interesting fact. Uh you don't think about this, but it's true. When you stand, your feet are closer to Earth's center than your head is. Okay?
>> You can calculate what the force of Earth's gravity is at your feet and the force of Earth's gravity is at your head. And there you'll get two different numbers. They're very close to each other. So, we don't think about this. It doesn't matter to us. Mhm.
>> But as you descend a black hole, the difference in gravity between your feet and your head gets greater and greater and greater. They're called tidal forces. And they end up stretching you head to toe. And initially it probably feels good, right? You just sort of stretch and then you realize, oh my gosh, this is unrelenting and it's getting stronger. Eventually you'll snap into two pieces likely separated at the base of your spine. If you sort of look at the structural integrity of human physiology and then you you're still falling and now those same tidal forces will operate on your torso and on your lower half. They'll stretch and they'll snap into two pieces. So go from 1 to 2 to 4 to 8 to 16 and you'll bifurcate in pieces all the way down to the center of the black hole. The worst part is, well, maybe equally as worse is you're occupying a narrower and narrower volume of spaceime as you go down to the singularity that is the center of the black hole. So, not only you get stretched head to toe, you're getting extruded through the fabric of space like toothpaste through a tube. Have a nice day. [laughter]
>> So yeah, you don't want to test that. All of our equations tell us that's what'll happen to you.
>> What's at the heart of the black hole? You said you
>> we don't know. So here's a problem. General relativity that gives us the black hole in the first place. If you follow the equations, the center of the black hole is infinitely dense and infinitely small. How does that even happen? We don't know. Maybe something prevents that. But that is the limit of Einstein's general theory of relativity.
>> So aliens um in our galaxy, is that possible that there's intelligent life in our galaxy?
>> I don't see I have no reason to doubt it.
>> Really? You think it's on a balance of probability, you think it's it's more probable than not?
>> Oh, yeah. Just given the size, like I said, given the age, the size, the ingredients, the uh how quickly life got underway. By the way, when you say intelligent, um, there's intelligent life on Earth, like do you know where we are in brain size
>> relative to other animals? Yeah.
>> Uh, we're not the top.
>> Yeah, we're definitely not the top.
>> I have no idea.
>> Yeah, we're like fourth.
>> Okay.
>> There's the whale.
>> Mhm.
>> And then [clears throat] the dolphin
>> and then the or the porpus and then the the elephant
>> and then us. So, if aliens came to Earth and they knew that brains are important, we'd be like fourth on their list for who they want to talk to. Just chew on that for a moment. Second, what we were told in school was, "Oh, but if you take the ratio of the size of your brain to your body weight, we're at the top." Well, that's our ego speaking there. We We didn't have the biggest brain, but we want to believe that we're smart. And so we is there some math magic we can perform on brain size to put us back at the top of that list? Yes. Ratio the size of your brain to the to the the mass of your brain to the mass of your body. Then we're at the top. However, what they didn't say is that no, we're not at the top of that list. We're only at the top of that list among mammals. They're midsized birds like the magpie and the parrots where the ratio of their brain size to their body weight is greater than that of humans. So look at the efforts we put in to just distinguish ourselves from all these other animals. And it's quite the exercise in ego stoking. You you want to think you're special in the tree of life that there are birds that fly and we can't fly. Nes can regenerate their limbs and we can't do that. And so badly do we want to especially with with military veterans, right?
>> Mhm.
>> Uh with missing limbs and things. You want to regenerate that. We can't do nes can do that. Crustaceans can do that. We can't do that. So, might an alien consider whales to be intelligent? Probably. But we add new extra elements to this. Do you have technology? The whale is not building telescopes, but we are. The whale doesn't, you know, have art, but we do. All right? So, we are a thing. We have what we call civilization. So if you want to ask are there intelligent aliens that have civilization that's yet another layer of that question is there intelligent life in the universe then you can ask is there intelligent life that has civilization that has technology because the Roman Empire they didn't know anything about electricity or computers or AI or anything and if aliens were sending them radio signals they're not sending radio signals back so the oper Operational definition of intelligence might include your ability to communicate across space or your ability to build a spaceship to move. The Romans were not building spaceships. So would they count as intelligence if that was an alien species somewhere else in the galaxy?
>> But is it plausible that there is intelligent life in this universe that hasn't got the capability of visiting Earth?
>> Yeah, sure. Why not? Sure. That's probably the standard.
>> How far can we have we gone? That's a great question. The fastest spaceship ever launched was the New Horizon's mission to Pluto. And one thing in space exploration, there's an unwritten rule. However you design the spacecraft, make sure it gets to your destination before you get old and die. Mhm.
>> Okay.
>> So, this spacecraft that went to Pluto was on the most powerful rockets available and they made the payload as light as possible so it could accelerate and so it got to Pluto quickly. If you instead took that and directed it to the nearest star, the Alpha Century system instead of going to Pluto at those speeds direct the nearest star take you 50,000 years to get there.
>> 50,000 years. The nearest star
>> to Earth.
>> Yes. To the sun.
>> And how many stars did you say there was again?
>> Well, 100 billion. Hundreds of billions.
>> And the nearest one took would take 50,000 years.
>> 50,000 years to reach.
>> Gosh.
>> Because space is empty. Right. So maybe there are intelligent aliens out there, but space travels too hard. So they haven't come to visit us. This is one of the uh hypotheses because if aliens are everywhere, well then where are they? I think they came to Earth and they saw all of our debris orbiting the Earth. There's a lot of space debris and they said, "I'm not coming. [laughter] I'm not going to risk my life." They just passed us by looking for another planet.
>> I've wondered about this space debris thing because it seems that every nation,
>> it's worse than you think.
>> But what I was going to say is every nation now seems to be racing to throw tens of thousands of pieces of metal satellites into our orbit. Is it a problem?
>> Well,
>> there's no laws, is there?
>> No, you have you have to ask who is it a problem for? Is it a problem? Yes. Who is it a problem for? Not the people who want high-speed internet in the middle of the ocean or in the Arctic or in the middle of the desert because these satellites, the SpaceX Starlink satellites are providing that in these remote places of the world. So, it's not a problem for them. It's a blessing. It's a problem if you're just trying to observe the night sky the way we've done as astronomers since time in memorial and I'm trying to get images of the night sky and I see satellites crossing back and forth. This amounts to visual noise in my data and if I'm trying to track an asteroid that might be headed our way and have thousands of other streaks of light in my image, there's a chance I might miss the asteroid. Also, uh, if there's some object of interest and a satellite passes right in front of it, that will contaminate the data that I seek. I don't know if this is reversible, but what it tells me is that the future of telescopes are going to have to be spacebor telescopes, which they we've already made that transition, and or the moon telescopes on the moon. They've launched five roughly 5,000 satellites, objects into orbit in 2025. We're on track to launch even more than that this year.
>> That's correct. We probably already launched that by now. We're we're this [clears throat] we're being recorded midyear 2026. I I we're already high up there. I So So the last number I saw SpaceX had 10,5 10 satellites. There'll be 100,000 active satellites in orbit by 2040.
>> Probably more. This is the utility of space not only for reconnaissance, for surveillance, basically military security, but also commerce. There is no Uber without GPS. So, it's not the value of the satellites themselves that matters here. It's the value of the economy, the economies that they enable. And that's why we have a space force now. A space force which had been percolating for decades. Uh Trump in Trump won decided let's make this official. And so he did. So now we have a space force. And people say does that mean there's going to be like Star Wars and everything? There already was a space force. They didn't call it that. It was called the Air Force Space Command. It was a sector within the Air Force. And so you pull that out. Now the the mission is a little more pure about what its goals are and what it needs to accomplish.
>> Have you heard about Kesler syndrome?
>> Oh yeah, of course.
>> Could you explain Kesler syndrome?
>> Oh yeah. Uh so 1978 uh I don't remember he's a physicist or a mathematician named Kesler who saw the increase in satellite launches that had been going on and he did a calculation and he said hm there must be some threshold of satellites orbiting the earth where if one of them gets destroyed by any means maybe two collide with each other or one intentionally taken out by a missile which has been happened three times now. Three or four times. Uh China's done it, India's done it, Russia's done it, and we've done it four times. We've done it to our own satellites, which means what? Think about it. If you can do it to your own satellite, you can do it to anybody else's satellite. It's a demonstration of your sovereignty in a way of your powers over what you might perceive as an aggressor. Anyhow, if you destroy a satellite, let's say it breaks into 10 pieces each going orbital speed. Orbital speed is is 17,000 miles an hour. That's way faster than a rifle bullet. So little pieces of satellite can be far more devastating than a high-powered rifle bullet shot into another satellite. All right, so these pieces scatter. If any one of them hits another satellite, breaking it into 10 pieces, you go from one to 10 to 100 to a thousand. Within just a few orbits, 100% of the satellites can be taken out. if you have enough satellites for that thresholding to take place. So in other words, if space is most if low earth orbit space is mostly empty and you destroy a satellite, the particles are not going to take out another satellite. They they'll orbit harmlessly or fall to earth harmlessly. But if you have another satellite in that path, then that destruction is going to take out other satellites. So he warned us of these thresholds. I don't think we're there yet, but we need to keep it on our radar. And the movie Gravity, it portrays exactly that scenario.
>> Objects in orbit travel at blistering speeds, 17,500 m per hour. Correct. And at that speed,
>> that's 5 miles per second.
>> At that speed, even a fleck of paint carries the destructive power of a bullet,
>> a rifle bullet
>> or a exploding grenade.
>> Correct. Correct.
>> A a fleck of paint.
>> Yes. Yes.
>> Okay, that makes sense. So if if there's one collision and there's lots of them up there, it's like a shrapnel. Is that
>> correct?
>> Yeah. A shrapnel is the is the is the best analog to that because it comes out and it damages other things beyond the target that was intended.
>> And there's no laws up there, is there?
>> Well, they're trying to, you know, space law is a is a wild west at this point. Forget orbit. It's like you go to the moon. Who owns the moon? Who owns a plot of land on Mars?
>> Maybe. Who? Well, they're trying to figure that out. Really? If I go to an asteroid and I want to mine it for its minerals, who owns those minerals?
>> So, they're trying to figure out who owns the moon.
>> Well, owns anything in space.
>> Anything in space.
>> Isn't it just who gets there first?
>> Yes, mate. [laughter] That's what I mean by the Wild West. If you love the D CEO brand and you watch this channel, please do me a huge favor. Become part of the 15% of the viewers on this channel that have hit the subscribe button. It helps us tremendously and the bigger the channel gets, the bigger the guests.