Instant Genius - Your questions – Everything You Wanted To Know About…Physics, episode six

Episode Date: April 29, 2020

Prof Jim Al-Khalili answers listeners’ questions about physics, the Universe and everything else. Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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delivering digital precision with analogue warmth, so you can experience exceptional sound at home. Music just as the artist intended. Visit nameadio.com to learn more. and welcome to the final episode of everything you wanted to know about physics, a new kind of podcast from the team behind BBC Science Focus magazine. I'm Dan Bennett, the editor of the magazine, and over the last five episodes,

you've heard Professor Jim Alcali and I talk about the building blocks of the universe, space and time, the quantum realm, energy, and the biggest mysteries of physics. Now, for a final goodbye, we're going to answer your question, sent to us via Twitter and via email. Now, this will be the last episode in this miniseries on physics, but we'll be back with more 30-minute guides to the most important ideas and discoveries in science and technology.

So do make sure you subscribe and leave us a review to let us know what topics you want us to cover next. And finally, if you want your questions answered in a future episode, be sure to follow us on Twitter at Science Focus. So the first one, this one's from Anil Sidu, who got in touch with us via email, and he asked, how does the Higgs give things mass? How does the Higgs give things mass? Well, more correctly, a physicist doesn't talk about the Higgs particle or the Higgs boson, but rather

the Higgs field. One of the way that quantum mechanics developed after its initial sort of foundation in the 1920s, is that it became what's called quantum field theory. So rather than talking about things as particles, even though that's a useful way of imagining, you know, particle collisions bumping into each other, it's a deeper way of thinking about the quantum realm is in terms of fields.

So we know that the photon is the particle of the electromagnetic field. It's sort of a lump of energy of the field, a concentration of the field. But actually, more correctly, all particles are sort of lumps of their own field. Even the electron is, you know, part of the electron field. The quark is a, is the particle manifestation of the quark field and so on, which is rather counterintuitive. But certainly with the Higgs, we should really be talking about the Higgs field. And you imagine the Higgs field is like a magnetic field.

So it's a region of influence spread through space, a cloud of higginess. I just made that up. That's probably not a very scientific term. But anyway, cloud of higgsiness. And so all other particles, as they move through the Higgs field, they interact with it in different ways. They feel its presence in different ways. In the same way that some metals feel a magnetic field

and others don't, depending on their crystal structure. So the way the Higgs field gives particles mass is that some particles interact strongly with it. They see the Higgs field as more treakily, you know, viscous. So they aren't able to move through it so easily because they're interacting so strongly. And that stickiness that the Higgs field gives them manifests itself in a greater mass.

Other particles, lighter particles, don't interact so strongly with the Higgs field so they can move through it more easily, like moving through water. and so that weaker interaction with the Higgs field means they have less mass. Particles that are massless, like the photon, they don't feel the Higgs field. That's why they can move through it. They don't interact with it.

That's why a photon, a particle of light, moves at the speed of light. So it's not the Higgs boson that is particles mass. It's the Higgs field, depending on how strongly they feel it as they move through it. Great, perfect. So this one is from Dom Condon, who I think it was one of your followers who jumped on board with this. He asked, well, here's what he said verbatim. Tries our might, I'm really struggling to understand how the universe can be 93 billion light years across, but only 13.8 billion years old.

How can light have travelled so far in such a short time? This is a popular question that comes up a lot. Yes, you would imagine that, you know, if we say the universe is 13.8 billion years old, the light from the most distant object is just arriving now, and it's, you know, so it tells us how long light has been traveling. Light has indeed been traveling for almost that time. And, you know, the oldest light is the cosmic microwave background. So light from the most distant object we can see certainly has only been travelling for 13-something billion years.

And it has only been travelling at the speed of light. The trick is that the object that emitted that light 13 plus billion years ago is further away now than 13 billion light years. Because in that period, in that intervening time that light has been travelling towards us, space has been expanding, has been stretching. So light has been coming towards us, you know, as though, you know, climbing a descending escalator. It's working against the expansion of space. And the space behind it that, you know, that it's, it's traveled through is also expanding. So by the time the light reaches us 13 billion years after it was emitted, the object that emitted it is much further away, hence the 90-something billion years.

years that we say is the real size of the visible universe. I'm glad to hear you get that one a lot too. We often get questions about that, the magazine. So we touched on this before. We see that light red shifts as it leaves distant galaxies and arrives at us. And so this, Ian Edmund had this question, which essentially, I think at his call he's asking, when photons leave that galaxy at a particular wavelength and therefore energy, and then they arrive here at a different one, and that process is what we call the redshift,

not the process, but what we observe. Where does that energy go? Or is this something that makes sense under one model or another, etc.? This is a really subtle question. And I suspect, you know, we're not going to get a full understanding until we have a proper theory of quantum gravity. Because in a sense, it does sort of come from different areas of physics. So, yes, it is true that light travelling through expanding space is being stretched. The Doppler redshift of space itself expanding. And so light will have a longer wavelength when it arrives here than it did when it left. And the very first equation in quantum theory that Max Planck gave us is that indeed the energy of light depends on its wavelength or its frequency.

They're interchangeable. So a longer wavelength light corresponds to lower frequency light and therefore lower energy. So certainly its energy is decreasing as it's traveling through empty space. However, we also know that energy should be conserved. Where is that energy going? It can't just disappear. And so the best guess, the way to talk about this is that that energy has somehow been used partly in the process of the expansion of space.

So it's stored within space itself. Now, what is driving the expansion of space? Well, it's, you know, initially it was the initial conditions of the Big Bang that caused it. Or, you know, when we talk about ideas like inflation theory and so on, the initial driving conditions that pushes space apart. And now we also know that space is expanding due to dark energy. So in a sense, space doesn't need any helping hand from the stuff within it for extra energy. But nevertheless, that's where we would believe. The energy lost from the electromagnetic field, from the photons traveling through space,

will have to be stored in the gravitational field, in space itself, driving its expansion. So the sums have to add up. That energy cannot be permanently lost from the universe. It has to manifest itself somewhere. And the only place it could be stored if the photons have lost it is in space itself. That was definitely a tough one. I think we definitely were chatting that one through on the team and thought it was quite a good question in the end.

So this, I can't say the Twitter handle of the person who asked this question. You probably know who you are. But they asked, if you pass beyond a black hole's event horizon, do some properties of space and time flip, you put an in quote, and this is something we get a lot, not specifically perhaps about spitting, flipping, but what happens past an event horizon? This is an interesting question. In fact, I remember first reading about some of this stuff

in a fantastic book by American physicist Kip Thorne, who's probably one of the leading experts on, Einstein's general theory of relativity. But those physicists who study black holes actually, you know, have to come across this a lot. And it's to do with Einstein's general theory of relativity and how gravity affects space time. The easiest way of explaining is to say, yes,

space and time do, in a sense, flip over. When we teach physics to physics students, we use diagrams called light cones, which are essentially sort of two cones, two cones, one inverted and one not, and so their apexes, their points are touching each other. And the way those light cones are angled tells you how space and time is changing and how it's flipping over. And once you get inside a black hole, things get very, very weird. in a sense, the direction that you're traveling in from once you pass the event horizon

towards a singularity in the middle, you would think of that as being a direction in space. You know, there's a singularity in the middle of this sphere. But these light cones flip right over so that that radial direction into the singularity becomes a direction in time, in a sense. And so that's why it's inevitable when you fall into a black hole that you're going to hit the event horizon. You're going to hit the singularity, I mean, in the same way that is inevitable that we're going to hit tomorrow. So tomorrow is in our future. We are going to get there.

The singularity is in the future rather than in the middle of space. So yeah, space and time get flipped over in a way that words really don't really, express adequately in the sense that time and space axes do do interchange. Great. And I suppose that's exactly what you were talking about in terms of, you know, you can seal this or at least theorise this all through, you know, the beauty of mathematics. So moving on to the next one from a man named Bruce, who had the Twitter handle, ugly. don't be so hard on yourself, Bruce. He asked about hawking radiation.

Now his specific question was, why don't antiparticles escape the event horizon, making the black hole bigger and the rest of the universe smaller? But I suspect it's probably good to just start off about what hawking radiation is and why it was of interest. So Hawking Radiation, named after Stephen Hawking, who first discovered the effect, theoretically.

We don't yet have the experimental confirmation of it. Otherwise, Stephen Hawking would have won a Nobel Prize for this discovery. The idea is that particles, we know in the quantum realm down at the subatomic scale, empty space isn't empty. It's fizzing with activity. Particles are popping in and out of existence all the time. They're being created and annihilated. Those are the technical terms. And these particles are created in pairs.

So you have a particle and its antiparticle partner. Both have mass, but they have otherwise opposite properties. So the other properties cancel each other out. All that's left is their mass, which is what was produced from the energy that made them. Likewise, a particle and antiparticle can annihilate each other. Their combined masses disappears in a puff of energy. It turns into energy via E equals MC squared. So quantum mechanics tells us that particles and antiparticles appear and disappear all the time everywhere.

Now, Stephen Hawking said, well, this must also be happening just on the edge of a black hole, just outside the event horizon. It can't, you know, if it happens, it'll happen inside the event horizon as well. But that's of no interest to us because nothing escapes the event horizon. And so whatever happens happens. But just outside the event horizon, particles and antiparticles would be forming and disappearing all the time. They said if one of them were to fall into the black hole and the other escapes. So if the antiparticle falls in and the particle escapes, normally the particle and antiparticle will have to recombine again. If they're created out of nothing, if there wasn't the energy.

to create them in the first place, they can still be formed according to the rules of quantum mechanics, namely actually Heisenberg's uncertainty principle. Heisenberg's uncertainty principle can be stated in a different way to the normal way we talk about it, which is that you can't know where a particle is and how fast it's moving at the same time. You can also say particle or energy can be created out of nothing, provided it's not too much energy. Or the more energy, or the more energy, you want to create out of nothing, the quicker you have to give it back to nothing to balance the books. It's a bit like borrowing money from a bank. But in this case, the bigger the overdraft you want, the faster you have to pay it back. And so the vacuum, empty space, can create particle and

antiparticle pairs, but provided they disappear again and that energy is given back to the vacuum very quickly. Now, if they are formed just outside of the, the event of a black hole and the antiparticle falls in and the particle manages not to fall in and escapes, then it doesn't have a partner to annihilate with. It can't give back the energy that it borrowed from nothingness. So what happens is the energy that it is left with now that it can survive. It's like Pinocchio. It becomes a real live particle. That energy must have been given to it from the black hole. And what we say is the black hole then must shrink. by a tiny amount, you know, its gravitational field is slightly weaker because it's given energy

to form this particle permanently. Now, the question is, what if it was the other way around? What if the antiparticles is the one that escapes? What is the same thing? Because antiparticles still have positive mass. They still have energy. And so if the antiparticle escapes, it will also have its mass, the energy that created its mass permanently given to it by the black hole. Of course, that antiparticle is likely to meet a normal matter particle because there's a lot more normal matter than antimatter, and they will annihilate. So it'll annihilate with another particle, another partner, not the one, you know, it's cheated on its own partner because his own partner sort of disappeared into the black hole. But it can annihilate with a normal matter particle somewhere else, and suddenly you've got some, you know, real energy.

Again, part of that energy is what the black hole's given up. So yes, the black hole will always shrink, regardless of whether it's the particle or the antiparticle that has escaped from just outside the event horizon. Well done, that's a real humdinger. Okay, so the next one is from someone with the Twitter handle Sard and Sari. So their question is, can a fast-moving object survive diving into a black hole? And is there anything called a gentle singularity?

Okay, well, no, fast-moving particles, nothing can escape a black hole if it passes through the event horizon. Doesn't matter how fast you're moving. In fact, you know, you fall into the event horizon. at the speed of lights and, you know, that's the fastest that can happen. You know, things at the event horizon and beyond it get very, very weird and very screwed. But you can't avoid falling into the event horizon. Now, there are different kinds of singularities for black holes. A singularity need not be a point.

If a black hole is spinning, then its singularity is what's called a Kerr singularity. K-E-Dabbar, New Zealand physicist who first developed the idea. And that singularity isn't a point, it's a donut, it's a ring. So it's a different kind of singularity. But I suspect the gentleness word in the question may be better suited to describing the event horizon, because you can have gentle event horizons and not so gentle event horizons. And that depends on the size of the black hole. So a normal black hole that was formed from the collapse of a star, falling through that event horizon will not be a pleasant experience. A lot of people now know, is it almost in popular parlance? Even when I give a talk to school kids, I say, what is the process that happens to you that stretches you when you fall into a black hole and you always get kids shouting? Spaghettiification, because spaghettification is the correct term. You get stretched as you fall through an event horizon of a, of a, of a,

of a collapsed star, because the gravitational potential is so different over just a short distance, the length of a human body. So if you fall in feet first, your feet are pulled much more than your head. And I suspect that's not a pleasant experience, not that I've tried it or not that anyone has tried it. But a super massive black hole, one that is, that we know now resides at the center of all galaxies, they are so big that their event horizon means a much gentler transition. As you fall through it, you probably won't even know the moment that you'd fallen through that event horizon

until you wanted to turn around and come back again and you realize it's impossible. So that would be a much gentler falling in, a much gentler event horizon than that of a stellar black hole, the black hole of a collapsed star. Okay, brilliant. And then last one from the readers. I suspect this might be someone we both know. From Jordan Colliver. And this is something that's actually quite popular in the building.

This is one of the questions I get most commonly asked by colleagues. And that is, would it be possible to make a generator using strong magnets to propel a turbine? or would the positive and negative fields cancel each other out? A few years ago, I wrote a book called Paradox, the nine greatest enigmas in physics. I don't remember what chapter was in, but I talked about perpetual motion machines,

which is a perennial sort of favorite of pseudoscience. People wanting to generate energy from nothing or, you know, without having to worry about conservation laws. The idea of generating a turbine from magnets alone is also an example of a perpetual motion machine, and it's impossible. The example I used in a book was a spherical shell of magnets, all with their north poles pointing inwards, and then having a magnet in the middle.

And, you know, there's an argument that suggests that men, Maybe you can have it perpetually rotating, extracting energy from the magnetic fields of the magnets in the shell. No, you can't do that. Certainly, you know, people ask, you know, where does the force come from? You know, when a magnet pulls a piece of metal towards it, a paper clip towards it, say, that requires work done on the paper clip to move it. That work is energy. Where does that energy come from? Well, it comes to the magnetic field.

so the magnet will be ever so slightly weaker. You know, if you pile a million paper clips or a billion paper clips on one magnet, it loses its magnetization because, you know, it's used up with its energy. But if you then remove those paper clips, you're having to apply work to pull them apart. So the energy you put into pulling them away gets fed back into the magnet. And so when you finally pulled the last paperclip away, that magnet has retained its energy. So magnetic fields do have energy, but you can't use that energy permanently to drive a turbine. That's why turbines are based on electric magnets that, you know, you have to transform between electric currents, electric currents, magnetic fields, and motion.

You can't get something from nothing. If you want to create electricity, you've got to put some energy in from somewhere else. and vice versa with a dynamo. If you want to get motion, you've got to put... Sorry, if you want to get electricity, you've got to put motion in. If you want to get motion, you've got to put electricity in. So the answer is no, there's no such thing as a perpetual motion machine. Brilliant, thanks.

And then, yeah, we're coming up to our time. So I'll give you two... You can choose between the last two. So these are just two from the team, so I thought I'd add one otherwise they'd tell me off. Which one would you prefer? Dimensions or Magnets? Well, I think I've probably covered the magnets one in the last answer. So let's have a go at the dimensions one.

Okay. So now, and just a final parting one from my team. If I didn't address their questions, I think I'd be in trouble. And so this one is another one, actually, along with the perpetual motion machine that I get. by, you know, people in different magazines who work with us. How many dimensions are there? When people talk, I mean, it's amazing. When people talk about dimensions, it's one of those terms that is bandied about without

any thought, you know, other dimensions, you know, where, you know, aliens must come from other dimensions or there may be other hidden dimensions. That's where ghosts reside. People don't understand enough about what it means to say. say a dimension. Now we know we live in, we are aware of our three dimensions of space. Any solid object is three dimensional. We know what that means, just as we know that a picture or something on a screen or paper is two-dimensional and a line is one-dimensional. So we know how a space is three-dimensional. Einstein taught us that time has to be regarded as the fourth dimension and we talk

about four-dimensional space time. It was one of the one. One of the three-dimensional space time. It was one One of the quests that physicists have been on for many years is to unify the forces of nature and something we talked about in a previous podcast. And in the early part of the 20th century, it was understood to mathematical physicists, Kaluza and Klein, came up with the idea that you could unify, in a sense, sort of, both the electromagnetic force and the gravitational force. But the way to do that is to add a fifth dimension. And so in their mathematics, they show that, you know,

the four dimensions of space time describe the gravitational field, but if you add a fifth dimension, then the electromagnetic force is a vibration in the fifth dimension. It's a very powerful mathematical technique that has proven useful in other areas, but their particular theory didn't have the legs to last. It's really sort of die the death. So the idea is that you can unify forces by adding extra dimensions.

And of course, that has led in the latter part of the 20th century to a number of different theories, very highly mathematical ideas, that show that there's ways of unifying the laws of physics, unifying the forces of nature by adding a number of other dimensions. So things like super string theory and super gravity, these are ideas that suggest there are many more dimensions than the four that we are aware of. String theories suggest there are 10 dimensions. Where are the other six? Well, they're curled up very tiny. We're not able to see them. You might say, oh, well, that's very

convenient, isn't it? But the mathematics is very powerful, and it is very beautiful. We don't yet know whether string theory is the correct theory of reality, whether indeed these other six dimensions do really exist. Further development on string theory in the 90s, something called M theory, where the M, no one can agree on what the M stands for. It can stand for, mother theory, magic theory, membrane theory. But M theory suggests there are 11 dimensions. You had to add another dimension to solve some of the problems in string theory. So the answer is, no, we don't know how many dimensions there are, depending on which theory turns out to be the correct one. And then there's all the ideas of, you know, in cosmology, of the multiverse, which again, something we touched on in a previous episode, which suggests that our universe isn't the only one.

So we have our universe with our four dimensions of space time, but there may be other bubbled universes floating in a higher dimensional multiverse. us. Again, mathematically, these ideas work. Putting extra dimensions in mathematically is very simple. It's just algebra. You can have an infinite number of dimensions. In fact, in quantum theory, there's an abstract idea called Hilbert space in which you can have an infinite number of dimensions. So the maths is cheap to add dimensions. But connecting that to reality, we don't know. All we can say for sure is that we have four dimensions that we're aware of. Everything else is speculation, both speculation in theoretical physics, mathematical physics, but also speculation in popular science and science fiction. And it's a lot of fun to talk about higher dimensions. Okay, brilliant. Well, that's all of physics covered in about

three hours, which is not about going. Thank you for listening. And if you enjoyed this podcast, do subscribe for future episodes. Down the line, I hope we'll be covering topics like the brain, diet, black holes and much, much more. And of course, do make sure you follow us on Twitter at ScienceFocus so that you can send us the questions you want answered. Thanks again for your support. And of course, if you want more guides to the big ideas in science technology, head over to our website, sciencefocus.com. or find us on Twitter, Facebook or Instagram. And if you want to dive deeper into any of the topics covered,

then Professor Jim Alcaloly's new book, The World According to Physics, published by Princeton University Press, is the perfect place to start. It's a concise introduction to the most important ideas in physics now, and Jim is a wonderfully clear writer who takes the grandest of ideas and makes them simple to understand. Thank you for listening to the Science Focus podcast, from the BBC Science Focus magazine team.

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