本周:宇宙中的一切旋转吗?How do lazy dogs keep fit? And is it safe to heat our dinner in plastic tubs? We've recruited 4 experts to tackle your science questions - astronomer Carolin Crawford, animal behaviour scientist Eleanor Drinkwater, geneticist Patrick Short and chemist Ljiljana Fruk.
In this episode
00:45 - Science show and tell
Science show and tell
with Dr Carolin Crawford, Cambridge University; Dr Ljiljana Fruk, Cambridge University; Patrick Short, Wellcome Sanger Institute and Heterogeneous; Eleanor Drinkwater, University of York
Let's meet the panel! Chris Smith was joined by Cambridge University astronomer Carolin Crawford, University of York animal behaviour scientist Eleanor Drinkwater, Cambridge University chemist Ljiljana Fruk and geneticist Patrick Short from the Wellcome Sanger Insitute and start up Heterogeneous. First up, Eleanor tells Chris about, in her opinion, the most adorable animal....
Eleanor - I have brought in a photo of the most adorable creature on the planet which many of you may not realize is actually the woodlouse. So if you flip over a woodlouse on its underside when they are pregnant the female actually has a pouch in which it will hold its babies before giving birth to them a little bit like a tiny tiny wombat.
Chris - And you can see this?
Eleanor - Yes.
Chris - A picture! Well this is a huge woodlouse, this has been blown up probably about 20 times, 50 times. So yes there's a little pouch on the underside between the front legs and there's lots of little they look like little white maggots but those are the babies. How long will they do there for?
Eleanor - Probably depends on the species but they wait until they have the first malt and so then they're big enough that they won't dry out as soon as they hit the outside environment and then eject the babies and they have to fend for themselves. Although they usually kind of stay near the adults because the babies actually enjoy eating the adults poo.
Chris - I thought you were going to say they enjoy eating the adults! Eleanor welcome to the program. Good to have you with us. Also here Carolin Crawford who's an astronomer at Cambridge University's Institute of Astronomy. And you've brought in something for us to see virtually.
Carolin - Well yes it’s a do it yourself show and tell. I bring you two planets. You have to go and look for them in the night sky. And it's just a really good time to remind people what's up in the night sky especially northern hemisphere. You've got the winter, it's dark late and it's dark early in the afternoon, and in the mornings. When you’re going home and it's dark. Look for Mars in the night sky over towards the southwest. It's brilliant. It's red. It's low down the horizon is really bright you cannot miss it and it'll be up till about 11 o'clock at night.
And then there are mornings, if you're a relatively early riser for about three hours before the sunrise you can’t miss it, apart from the moon it’s the brightest thing the night sky. Low down towards the south east direction so you can see Mars and you can see Venus either edge of the night. And just one more thing. My favorite meteor shower is coming up and it's the Geminids. They peak for a couple of weeks, 13th 14th of December. I love this one it's quite predictable, go out late at night preferably after the half moon’s gone down and you begin to see them. They peak around two o'clock in the morning but you don’t have to stay up that late you can start to see them really towards after about 9 o'clock at night. And when the meteors come they're quite slow and they're quite bright. And so you can’t miss them. So that's coming to a sky near you very soon.
克里斯-他们对应的尘埃's just now patch of the solar system so that as the earth goes round in its orbit it sort of sweeps through that cloud of dust and that's why we see them every year at this time?
Carolin - Yeah well this is a particular trail of debris that's left behind a little asteroid called 3200 pantheon. It's disintegrating and it’s got this cloud that's followed its orbit. And every year we go through it and the same time of year. And then you get all these little bits of grit falling into the atmosphere and just producing these wonderful shooting stars and it's all happening about you know 100 kilometers up.
Chris - Wonderful. Carolin thank you. Welcome to the program as well. Patrick short is a geneticist from the Wellcome Sanger Institute. He also is the CEO of a startup which is called Heterogeneous. Interesting name for a genetics startup, what does it do?
Patrick - So it helps people learn more about their genetics and health and also it gives them greater control over their data. So it allows them to control who gets to access it and what it's used for.
Chris - And when did it start, the company?
Patrick - About a year and a half ago.
Chris - And how does it make money?
Patrick - So researchers use this data for all sorts of purposes and actually there are a lot of companies already that sell people's data they just don't realize it. So what we do instead is allow people to sell it on their own terms or to participate for free if they already have a disorder. For instance a lot of patients are just mainly keen to get their data out there so it can be used and get closer to a cure.
Chris - I thought Facebook had the angle on this?
Patrick - They're certainly trying. So are Google and everyone else. But we're hoping we can give people more control.
Chris - Have you brought anything with you?
Patrick - I did, I brought a little stuffed animal actually. It's a water bear - a tardigrade. One of the things that got me really excited about biology in the first place so this little animal can survive radioactive bombs, it can survive being dried out and frozen then heated up thousands of degrees, no matter what you throw at it basically it still survives. I always thought it was quite amazing that an animal has figured out how to survive such extremes. I think we're still from a genetics perspective trying to figure out how it does all these things but it's quite a cool little creature.
Chris - And at last but not least Ljiljana Fruk is from Cambridge University. She's a chemist and she has a penchant for nanotech and biotechnology as well. You have got an array of tubes, you've brought in a stereotypical chemist’s rack of tubes. What's in there?
Ljiljana -I thought I need to show what chemists are still about, and that’s tubes. So I do have a selection of some of my nanomaterials that we prepared in the lab. So I have carbon diamonds that get really people excited all the time. And unfortunately they look like a bit grey.
Chris - I don’t mean to rain on your parade or anything Ljiljana. But this just looks like you poured some milk in to be honest!
Ljiljana -But if I tell you these nanodiamonds were made in a huge explosion in a special chamber and they are used for biosensing of small parts of cells, you would be a little bit more impressed.
Chris - How did you make them?
Ljiljana -So we actually buy them from the company that makes them in the big explosion chambers, but we modify their surfaces so we need to make them stable and adjustable to enter the cells. So there’s a lot of chemistry out there.
07:55 - Feeling gravitational waves
Feeling gravitational waves
Chris Smith put this question to astronomer Carolin Crawford...
Carolin - Oh very good question. So if you are near a big event, well let's, we’ll worry about how close in a minute, but let's work out what a gravitational wave does to you. And the thing about a gravitational wave is that these are travelling disturbances in the shape of space. They stretch and they squeeze space and everything in it. So if I am facing an incoming gravitational wave and imagine I stretch my arms out, I am going to be stretched and squeezed alternately from one fingertip to the other tip while being squeezed and stretched in the opposite direction from the top of my head to the tip of my toes. So I've got that action going on - stretching, squeezing - and there’s also another mode which will stretch and squeeze me from my shoulder to the opposite hip and then from the other shoulder to the opposite hip. So you are being shaken internally like a jelly, you've sort of been wobbled in all these different directions.
However this is happening to all of us all the time, right. And you're not feeling it are you?
And this is because, these gravitational waves, most of them are incredibly weak - I mean the kind of length you get stretched. Well we had, the first detection was two 30 solar mass black holes that collided with each other a billion light years away and that's one of the best detections we've had so far, the most sensitive detectors, and that stretched and squeezed a 4 kilometer long laser by a distance less than a millionth of an atom.
Okay so gravitational waves are very weak. So then. But you know Paul was very clever. He said what if you're close to a gravitational wave event and magically we’re somehow protected to whatever is, you know where these black holes are colliding. Then it starts to get a bit more interesting because gravitational waves, well the, you know how much you get stretched and squeezed depends on one over the distance. So if you had an event like two 30 solar mass black holes colliding somewhere where the sun is, so one hundred fifty million kilometers away, the amount of distortion you might feel is of the order of tens of nanometres. I don't know whether you'd feel that.
Ljiljana -My nano-diamonds might feel it, because they are very small.
Carolin - They're very small, but whether you might feel it in your body… So let's move the event a little bit closer and maybe it's a few thousand kilometers away, then the amount of distortion gets to be about a millimeter over the length of a body. Again whether you feel that or not, it's really got to be a few hundred kilometres before you start being stretched and squeezed over you know sort of 180 centimeters or so by one centimeter. Now I'm reckoning you would feel that. I also don’t think it would be very good.
Chris - Probably wouldn't be very good for you would it, for your body to have that?
Carolin - No. Would your muscles stay attached to your bone? What would it do to the brain? And you know the absolute last thing I haven't told you about is the frequency that these gravitational waves are doing the stretching the squeezing. This is on sub millisecond time scales.
Chris - Because they travel at the speed of light, gravitational waves, or thereabouts, don't they?
Carolin - They travel at the speed of light.
Chris - Therefore your body would be stretched and squeezed at the speed of light. So you probably wouldn't be, if it was going to squash and squeeze your brain at the speed of light then it probably would mean you weren't aware of it.
Carolin - No, the gravitational waves travel out from the disturbance at the speed of light. What I'm talking about is the, you know between the stretching and squashing, that would be, you stretch and squish on basis of you know less than, you know submillimeter seconds. So I don’t think your body would really survive that. So I think the answer to your question is you will be wobbled like a jelly, shaken from the inside out and I don’t think it would be very good news.
12:01 - Cooking - plastic fantastic?
Cooking - plastic fantastic?
Chris Smith put Katie's question to chemist Ljiljana Fruk...
Ljiljana -Before I go into this question, we have to say that plastic is basically a common name for a large group of polymers and they are all a little bit different. So in a chemistry lab we will use these polyethylene containers, which are really inert and they don't have any kind of additives that will leach, they are very stable, but of course if you have a food containers or bottles or even some of the foils that you use for microwaveable food, they are made of different polymers. One is polycarbonate. It's kind of this transparent material. And to make this polycarbonate you usually need to use other additives, small chemical additives in the process.
Chris - They are called plasticizers.
Ljiljana -Like plasticizers. So they are embedded in the polymer, but some of them will be staying there and so if you heat up the polymer they can leach out. And one of these, and you might have heard of this, is bisphenol A, which is now kind of on the list of banned substances and you will find also lots of materials which are free of bisphenol A. But this didn't solve a problem because now you have other additives that might have a similar effect and the effect is that they disrupt our hormone cascades. So you know our emotions are controlled with hormones. So bisphenol A will basically mimic the hormones and activate them. So it's called an endocrine disruptor. So if you have too much of this in your food it’s of course not very good. So the answer is, yes you might get something, but of course it depends on the type of container and material.
Chris - Eleanor?
Eleanor - Is there any way of knowing which one I can cook my food in or which one I can't or...
Ljiljana -Usually you will have the notice on the bottom, if you check, and it tells you if it's safe to heat. It's not that we are given something that is not controlled. There are some safe amounts of these chemicals that can enter the food chain and they usually do. You know and we continously get stuff and our body can deal with it. It is just that, yes, you know there are possibilities that if you have a particular food that might react with some of these compounds, you might get some side products. So, I would you know, I would microwave my things in the glass dishes, if I have to, for example.
Chris - Happy with that Katie?
Katie - I think I am going to go home and rearrange my kitchen.
Ljiljana -The precautions are taken. So you know things are under control. I wouldn’t throw out all of my Tupperware out.
16:27 - How do earthworms move?
How do earthworms move?
Chris Smith put Paul's earthy question to animal behaviourist Eleanor Drinkwater...
埃莉诺——好吧,如果这是一个聪明的问题you think about it, like you know, how does this little blob of pink kind of manage to wiggle its way through such hard earth. And the answer is: it's all about fluids. So if you've ever had a water balloon and you grab one end the other end kind of shoots out, and that's kind of what's going on in worms. So if you look really carefully you'll see that they're segmented all the way down their bodies. It has two sets of muscles, one that'll make the segment kind of long and then and the other one will make it short and fat. And so it's a kind of combination of these muscles working interchangeably, changing the shape of the segment without changing the volume of the segment.
Chris - So you've got a muscle that goes, or muscles, that go along the length of the worm and when they contract them make it short and fat vs. muscles that are in rings around the world making it get thinner and longer when they squirt or squeeze.
Eleanor - In principle, yes.
Chris - And it's using the antagonistic effects of those two to change its shape. How does that push a tiny worm through soil?
Eleanor - So it's a bit like an accordion, the way that they all kind of contract together and space out, and it's just incredible to think about the fact that each segment in this worm can move and contract independently. I just think it's mind blowing personally, it's amazing.
Chris - Don’t they eat their way through the soil as well? Because you know when I lived in Sydney these people introduced me to their wormery and said we put all our household rubbish on this and they turn out worm juice and this is plant magic, it's like gold dust for plants it makes everything grow.
Eleanor - Yeah they do eat vegetation in the soil but they can also whittle through it as well.
Black hole or wormhole?
Chris Smith put this to astronomer Carolin Crawford...
Carolin - The event horizon is, if you like, the horizon beyond which you can't detect any event so it is the invisible boundary around a black hole. It’s the point of no return. If you step over that. Yes the short answer is you get killed you become part of the black hole, but the trouble is that no information can cross from the inside of the event horizon to the outside, so as the questioner says: we don’t know what goes on inside the event horizon. What we suspect is there’s lots of empty space and right at the center you've got what's called the singularity, it's the black hole itself, it's infinite mass crushed down to tiny tiny volume.
There are ideas that, say your black hole is rotating and maybe the singularity gets stretched out like a ribbon, it would be possible to cross over the event horizon, perhaps fall through and avoid becoming part of the black hole and perhaps pass through something called a wormhole which is like a tunnel through to elsewhere or ‘elsewhen’ in the universe, and get spat out in the opposite of a black hole which is a white hole. So you have this idea you fall into the black hole. Go through the wormhole get spat out to the white hole. Now all of this, if you look at the maths is okay. If you look at Einstein's equations they can predict black holes. They're also produce white holes. The only snag about white holes is you have to run time backwards instead of forwards so it's a bit of a snag for them actually existing. And also we see black holes everywhere in our galaxy. Everywhere in the universe. We don’t ever see a white hole. So then you’ve got to start questioning whether wormholes exist.
Now they’re a really nice idea, you see them in science fiction books and movies - how you get around the universe or how you travel in time. In practice when you look at the equations, and I'm simplifying grossly here, they are very unstable. You put a toe in a wormhole it will just collapse around you so I dont think its a good way of getting round the universe. So the answer, we go back to the fact that yeah if you did go over the event horizon, I think you can become part of the black hole, it’s going to kill you. Yeah, in fairly dramatic ways! And just to remind everyone a black hole, despite the name, is not a hole in space it's a thing. It is you know an area of extreme mass, extreme gravity, and you would just add to that mass and gravity.
21:24 - How dogs keep fit
How dogs keep fit
Chris Smith put James' question to animal behaviour scientist Eleanor Drinkwater...
Eleanor - Well if you think about it a lot of breeds of dogs are built for speed, so something like a Greyhound can hit about 45 miles an hour. So even an unfit Greyhound can still be much more speedy than the average or relatively fit human. And like humans with more exercise dogs become more fit and with less exercise they can also become more fat. But on a wider level how do animals in general stay fit? There are some amazing adaptations out there. Two of my favorite examples are something like barnacled geese when they're preparing to fly really long distances, they only need a couple of minutes of flight a day to build up enough muscle in order to become fit enough to migrate which I just find crazy and so unfair. And then on the other hand you have some animals that do this amazing trade off in how fat they are vs. how thin they are depending on predators. A good example of this is porpoises around the UK. If they're in areas in which they are at risk of being killed by dolphins they tend to be much more sleek and much able to get away from dolphins than in areas in which there are less dolphins. So basically the animal kingdom is brilliant and there are loads of interesting adaptations to fitness.
Chris - So they basically evolved in order to give themselves the ability to do that because it's beneficial to them to do that and were it not beneficial for them to maintain this, you know I guess that's probably because we keep opening the carton of dog food isn't it? I mean if we didn't keep feeding them they would lose condition and the fact that they can afford to maintain all this muscle bulk which is energetically very costly to maintain all those muscles and things that they're not using. We on the other hand as humans we just run to fat if we don’t take regular exercise.
Eleanor - Yeah we we have quite a sedentary lifestyle compared to most of the animal kingdom.
Ljiljana -I just said to Patrick, “Blame it on DNA”.
Chris - So, Patrick, you’re being made the butt of this.
Patrick - Well I was going to say that we humans probably spend most our energy keeping our brain intact, right? We don't have to do much to train it and it will still do most of the essential functions so maybe the dogs are spending less time training its brain and more on the muscles.
Chris - It's an energetically very costly organ the brain isn't it? You think it's running at roughly 20 Watts because it's about 20 percent of your oxygen consumption and your average person is running at about 100 watts it's about 1 or 2 watt per kilo in the average person. So your brain is burning a lot of energy.
Eleanor - Yeah in some cases like for example sponges, people thought that there's some evidence to suggest that they had a neural system or even kind of a brain-like structure, but because it's too energetically costly so they've got rid of it, so you know we don't need a brain!
24:34 - Cystic fibrosis in Ireland
Cystic fibrosis in Ireland
Chris Smith put this question from Dee to geneticist Patrick Short...
Patrick - Yeah absolutely. It's a very good question and this is also the case for example in places like Finland as well as many Greek islands or other places, anywhere where you've had, at least in the past, some kind of either relative isolation or else a big population bottleneck. If you had a small number of people that go and colonise a place to begin with then the amount of genetic variation that went into that colonizing event means that certain disorders that may have been relatively rare to begin with just happen to end up being common. So the example I'm most familiar with is Finland, but I think it probably applies in Ireland as well, but only about 2000 people colonised the country some tens of thousands of years ago. Then if one or two of those people had a particular disorder then as that population expands it can be at quite a high prevalence and also the existence of any kind of clan structures or mating structures that mean people are more likely to mate with one another. Can cause these to increase further still.
Carolin - So is that also the case for Iceland, because I have read that that's quite a closed gene pool isn’t it? And it's of great interest to researchers for that reason. Do they also have this issue about these diseases?
Patrick - Yes and the genetics research that goes on in Iceland is quite amazing. They're very soon going to have genome sequenced the entire population. They also have genealogical records going back for many generations but I believe it is the case there as well that there's a number of disorders that are at particularly high prevalence that there are specific research priorities for that country.
Chris - Is it worth considering also that these genes that we regard as disadvantageous under certain circumstances the reason they might be in those populations and have risen to such a high prevalence could be because in the past one other function of those genes is to confer some kind of advantage under certain circumstances and therefore they become concentrated in the population and while they're disadvantageous if you have the right environment they're advantageous under other conditions.
Patrick - Yes that's absolutely right. One of the best examples of this is is the gene that causes sickle cell anemia that also confers a resistance to malaria. So you can, if you have two copies of the gene, of the mutation, then you're likely to have sickle cell but if you have one it's actually protective from malaria. So you end up with this balance. But in places in the world where malaria is not an issue then it's often at much lower prevalence and there's lots of other great examples.
Chris - I was thinking that specifically one of the diseases that Dee mentions in her question is cystic fibrosis and we've learned in recent years that the gene that is linked to cystic fibrosis happens to also confer resistance to certain salmonella infections. And so we think that's one of the reasons why that gene is so common in the population because people would have had some degree of resistance against typhoid for example historically. So it became more concentrated in the population.
Patrick - Yes. The other interesting thing about cystic fibrosis is there’s a single mutation that is, that accounts for a large fraction of the cases. There's all sorts of mutations that can cause it. But whenever there is a single mutation that's very common, it's often, can depend on the frequency within a particular population how frequent that disease is in general so probably that delta 508 mutation that's quite prevalent cystic fibrosis happens to be very common in Ireland for reasons that we may or may not have figured out yet.
28:59 - A day on Mars
A day on Mars
with Carolin Crawford and Ljiljana Fruk, Cambridge University; Patrick Short, Wellcome Sanger Institute; Eleanor Drinkwater, University of York
Chris Smith put the show panel to the test. Who will be The Naked Scientists' Big Brain of the Week? On team 1 - geneticist Patrick Short and astronomer Carolin Crawford. On team 2 - Ljiljana Fruk and Eleanor Drinkwater...
Chris - So the first one, this is round one, this is called a matter of time this round. So Carolin and Patrick which can live longer a shark or a tortoise?
Carolin - Are we allowed to confer on air? He’s whispering at me!
帕特里克-对不起我窃窃私语。
Carolin - We tend to think it's going to be tortoise...
Patrick - Maybe he’s tricking us.
Carolin - Yeah, and sharks also live pretty long, but I think I'm going to go for the tortoise because there’s one that lived over a century isn’t there? One of Darwin's tortoises?
Patrick - Yes I think I’m with you on that.
Chris - So are you going to go tortoise?
Carolin - Well giant tortoise, very specific, very long lived giant tortoises.
Chris - Well let’s find out!
Patrick - Aww I knew he was tricking us!
克里斯-碳约会死sp的眼球ecimens, scientists recently showed that Greenland sharks live for more than four hundred years. Female Greenland sharks are estimated to be at least 150 before they begin to reproduce. No you're quite right about the tortoises though Carolin because in the wild, giant tortoises do have a long lifespan. It’s at least 100 years or more. And in 2016, Jonathan the giant tortoise in the Seychelles was said to be the oldest living animal. He was more than 180 years old. So you didn't get any marks but you did show good knowledge. That's a good start. But perhaps you can do a bit of improvement in round two.
Team Two this is Ljiljana and Eleanor. Which lasts longer a day on Mars or a day on Venus. What do you think?
Eleanor - Can we answer the shark question instead?
Chris - Anyone would think we'd decided which questions to put to who.
Ljiljana -Wait, day on Mars?
Chris - Day on Mars or a day on Venus which is longer?
Eleanor - Which one’s bigger?
Chris - Well that’s the question Eleanor!
Ljiljana -I’d go with a day on Mars.
Eleanor - I like your definite answer, I trust you, you seem confident!
Ljiljana -Carolin is waving.
Chris - Carolin, why are they wrong?
Carolin - Because a day on Venus lasts longer than its year. So Venus goes once round in about two hundred forty odd Earth days, which is longer than it takes to go once round the sun which 225 days.
And a Sol, a Martian day we call a Sol, that's about the same length. It’s within half an hour or something of the day on Earth.
Chris - Thank you Carolin. I now don’t have to read the answer, which saves a bit of time.
Round two, animal magic, team one, Patrick and Carolin, which of these unattractive sounding animals is real and which one did we make up or are they both made up - the scrotum water frog or the bloated flatfish? What do you think?
卡罗琳——不要看着我!我相信somewhere in the universe there are planets where both exist, you know. You can't tell me unambiguously that none of them exist.
Patrick - So we have the scrotum water frog is that what you said?
Chris - Yes the scrotum water frog.
Patrick - And the bloated flatfish, you just wanted me to say those on air didn't you.
Carolin - Yeah I think bloated flatfish doesn't sound a total stretch the imagination.
Patrick - But maybe he's trying to trick us again.
Carolin - We’ll take that as an assumed, yes, but it could be a double bluff.
Chris - What are you thinking then, the frog or the fish?
Carolin - I would go with the fish but I am not an expert.
Patrick - Okay, let’s say the frog is not real the fish is real.
Chris - So you’re going with the frog is made up?
Patrick - Yes.
Chris - No, the scrotum water frog lives in Lake Titicaca in the Andes. It's evolved a reduce lung capacity and it’s compensated by having very highly convoluted skin folds and I don’t why I’m looking at you Eleanor, you’re the biologist in the room.
These convoluted skin folds help it to breathe hence its name. And apparently these frogs do press ups on the bottom of a lake that creates disturbances in the water. This increases the delivery of oxygen which it then absorbs through it’s skin.
You're doing very well team, you've got zero. Okay back to Team two, see if you can improve on the score of zero overall so far. So Eleanor and Ljiljana, true or false, cats lack the ability to taste anything sweet?
Eleanor - Oh that's true. That's totally true.
Ljiljana -Yeah, I would go with Eleanor.
Eleanor - Because they did an experiment on lions in which they gave them the choice of water with sugar or water without sugar and apparently they couldn't tell the difference, or they behave similarly to both and so they assumed that they can’t taste sweet. The similar question which hasn't been tested, which I’m dying to test, but no one has let me do it yet, is can penguins taste fish? That's another question. No one knows.
Chris - But Lion bars taste sweet.
Eleanor - I think that might be a bit different.
Chris - So you're going for actually that's true? Cats can't taste sweet stuff.
Yes, you are off the bottom, you have one point. There are two genes which are used to make a working sweetness detector which is on the tongue. Cats lack a working version of one of them so they can't tell sweet from non sweet despite experiments like the ones you outlined there Eleanor where people have tried to get them to discriminate between sweet and non sweet things and they can’t do it. Very well done.
Back to Team One. You've got to save your rep here. It is all on this one. So this is called solve this, this round. This is a riddle slash a thought experiment which you got to work out what the answer to this is.
A cork dropped into a glass of water always drifts off to the side. So how can you make sure that the cork will always float in the center of the glass and to solve this riddle you only need glass, water and cork. What are you thinking?
Patrick - Do you have any of the Jeopardy music while we think?
Carolin - Do you have a cork? We could quickly experiment.
Patrick - So it always drifts to the side.
Carolin - How about you stir up the water before you drop the cork in and then you're not going to get motion out to the side of the glass.
Chris - No spoon provided, no fingers, just water.
Patrick - No fingers…
Carolin - How are we going to drop the cork in then?
Chris - With your mouth... no I don’t know. That’s not the answer I was thinking. It’s a good idea, but not the right answer.
Carolin - So I can't drink the water and then if…
Chris - It's got to float.
Patrick - Is it a normal glass, or can we change the shape of the glass in any way?
Chris - No, you get the same glass.
Patrick - Right. This is quite a conundrum yeah.
克里斯,我要快点你。你know the answer?
The answer is that you fill the glass right to the brim, because think about it, the surface tension means you'll pull the water into a curve, the cork always floats to the highest point in the water and the reason it goes off to the edge is because normally the water forms what's called a meniscus where the edge of the water is higher than the curved surface, which is why the cork goes there. Because of surface tension you can overfill the glass so it bulges above the rim and the cork will float to the top, dead center in the glass that way.
Patrick - That was pretty clever.
Chris - Yeah I'm glad you appreciate that. It's lovely. Right. No marks for you then. Right. You could be clinching it by the looks of things. Do you want to have a go anyway? It’s quite fun this one isn't it. So Eleanor and Ljiljana, this is purely just to show off now.
If you balanced a mop horizontally on your finger and you then cut the handle at the point where it was resting on your finger, so you effectively get two bits - you get a long bit of handle and then the short bit of handle with the mop head. Are you with me? If you weighed the two pieces - the short bit and the long bit - which would weigh more, the long bit or the short bit, or would they weigh the same?
Eleanor - If you could balance it… I feel like this is a trick question. This is a sneaky question. I feel like you want us to say the same, but I don't think it is. Is it something to do with mass and things? I don't know. Does it depend on the mop? What the mop is made of?
Chris - It’s a normal mop.
Are you going to say they weigh the same?
Eleanor - No no. It can't be the same because that’s too easy.
Chris - Same? Different? Going to have to hurry you.
Eleanor - I don't know. Maybe we should just go same.
Chris - You're saying same.
Unfortunately, you lost your edge right at the end. So what do you think? You've got an answer Patrick?
Patrick - The mop head is gonna be heavier.
Chris - Yeah I'd love to give you a bonus mark. No, I’m not going to let you get away with that one otherwise Carolin would've clinched it for you earlier wouldn't she? But the short bit actually weighs more. And this is why you have to put your finger so much closer to the mop head because there's a leverage effect. If you think about the length of the handle it's much lighter the long handle but because it's acting over a long distance there's a bigger torque. So it will actually weigh a lot less but it has a longer leverage. It's like Archimedes said if you give me a lever long enough and a place far enough away to stand I could lift the Earth. And that's the same principle. So actually it's a trick. It wouldn't weigh the same. The mop head plus a short bit of handle would actually weigh more.
Universal spin
Chris Smith put this question from Shawn to astronomer Carolin Crawford...
Carolin - Well let's leave black holes out things for a minute. Because yes a lot of stuff is spinning in the universe, right on the scale of not just planets and moons and solar systems and stars, but also whole galaxies are spinning. And it’s really a question of something called angular momentum. And this dictates that if you’ve got a body that’s spinning it’s telling you what rate it's spinning in and what direction, and angular momentum is a conserved property. This means that once the body has got angular momentum you can't get rid of it, unless you kind of apply an external force, and the way angular momentum goes if you have something that's very large that is spinning just a little bit and it shrinks down, then it spins faster.
So you've got this conservation, and the nice thing about astronomy and space is that things in space are made from gravity - so you start with a big gas cloud, then a tiny little tug gravity to one side to the other: it's got a very lazy spin. But as it collapses down to form a star or even a big scale galaxy, it starts spinning up faster and faster. So that's the basic reason why so much spins in the universe, because it's more likely that the original gas cloud is going to have the tiniest torque on it than not. So when you get to black holes, we think every black hole spins because they form from massive stars and massive stars are formed from these gas clouds. So if you have a star that’s spinning and then collapses down to a black hole it's going to spin even faster, and black holes can spin incredibly fast.
So going back now to the original question - can they break up nearby objects? Well they're going to break up nearby objects because of their gravity, not because of their spin. And as we discussed earlier it's not very good if you go over the event horizon of a black hole, you get what’s known as spaghettified! You know so things get broken up because of the gravity they're going to get pulled onto the black hole. They're not really going to get ricocheted away.
Chris - In the quiz there was the question that you answered for me about Venus, and you made the point that actually it's turning excruciatingly slowly so a day is almost longer than a year. How did it end up going so slowly then?
卡罗琳——我的意思是金星在佤邦基本上是旋转lking pace - the Earth spins about a thousand kilometers an hour, Venus is literally walking pace, not just that it's also going in the wrong direction. This is really cool!
Chris - The sun rises in the west on Venus doesn't it?
Carolin - That's right - rises in the west sets in the east. And so if you look down on all our solar system, the sun is spinning in one direction, all the planets are going round the sun in that direction, all the planets are spinning that direction, just Venus is going the wrong way. So, we don't think it formed different from all the rest of the planets because we assume they just inherit the same rotational motion from the original kind of nebula that collapsed to form the sun and all the planets. There’s something that's happened to Venus subsequently that has slowed down its rotation, even just turned it the other way and it could be due to it's really thick atmosphere. You've got the gravity the sun creates - what we call tidal bulges, it kind of pulls this thick atmosphere in the direction of the sun. And if that is rotating at a different rate than the planet’s underneath rotating friction between the atmosphere and the planet, it just slows it down. We’ve got the same effect on earth, you know between the moon pulling the oceans round to form tides. That's breaking the Earth's rotation slightly every year, but in Venus it's much more extreme. You got this really dense atmosphere and so that is probably the most likely reason for it to have been slowed down and then just slightly started spinning the other way.
Chris - But for the reason you've outlined, something else will have inherited that angular momentum from Venus and something else will be spinning the equivalent amount won't it?
Carolin - Yeah it could be, and it could well be transferred to the sun. So whatever’s perhaps slowing down the angular momentum - you'd treat Venus and the sun as a closed system maybe it's going to spin the sun up slightly.
Telling apart twins
Chris Smith put Steph's question to geneticist Patrick Short...
Patrick - Yeah it's a great question. So twins have had a very special role in the history of genetics. They've helped define this concept of what we call heritability which is basically how much does variation and genetics explain variation in a trait? They've helped define that for a huge number of disorders, in the early days it was often identical twins that were compared to non identical twins which are basically like siblings but that happen to be born at the same time.
And so when you compare those two groups you can basically say OK the identical twins have the exact same DNA with the exception of maybe a small number of mutations that one or the other might have, whereas the non identical twins are basically like brothers and sisters so they share half their DNA and that allows you to calculate if a trait varies about the same amount and identical and not identical twins then it's probably not genetic at all and if the identical twins are very close it has more of a genetic basis.
But what is often forgotten is almost every trait has an environmental component. Know you could anything we can think of whether it's cancer, cardiovascular disease, even our personality traits are molded by our environment. But there's a third factor which is just randomness or what we might call stochasticity. So even if you're studying a trait that you think has a huge genetic component to it, maybe face structure for example, and what people might think of as something identical twins should be very similar in, there is always an element of randomness in development. That means even if something is supposedly perfectly genetically tuned which which probably even facial development isn't then there's an element of randomness that just means you're going to end up with differences over such a long process of many years of development.
Carolin - So does this include something like freckles or moles on a face? Because in my experience that's been a way to identify them?
Chris - I was thinking exactly that. Yeah yeah. We used to tell two kids apart at school because one had a mole. Is that an example of what you mean by this randomness?
Patrick - Yeah that's right. It could also so could be something like freckles or moles that might represent a mutation in an individual skin cell. So that's what we call somatic mutations. So yeah I'm not sure exactly how how a mole arises. But freckles for instance have to do with the mutations that change the way pigment accumulates in the cell.
But there are other beyond just genetic changes on a cellular level. Simply the morphology of your face, how every cell you know at some point you're a single cell and then you're two and then you're four and then you're eight and the way those cells move around and arrange and become your body in your face, it's impossible to program perfectly.
There's there's a lot of great photos on the internet. If you take Obama's face and you kind of slice a line down the middle and copy the left side of the face across to the right or if you do the same and copy that right across the left, they look like completely different people so even your left side and right side of your own face if you were to duplicate it to the other side you'd look completely different.
47:08 - Cats vs dogs
Cats vs dogs
Chris Smith put forum user Neilep's question to animal behaviour scientist Eleanor Drinkwater...
Eleanor - This is a really lovely question and in fact this has been an area of a bit of debate in biology as some people have been suggesting that it might be that dogs are kind of special genetically, perhaps they mutate a bit quicker. But I'm afraid the consensus at the moment is a little bit more boring but still quite cool. It's because of us and it's because of selective breeding. So if you think about what dogs have been bred for so you have Huskies who have been bred to pull sleds. Or dogs who've been bred to to hunt deer or go down rabbit holes, it’s a real variety of things that they've been bred for, whereas cats perhaps they've been bred for not quite so many chores.
Chris - Cats just won't cooperate with anything, in my experience.
Eleanor - If you look at something like horses for example, something like a shire horse who has been bred to carry huge loads or like a Shetland pony and get a bit more of the same size dimorphism than you do it in cats.
Chris - Thanks Eleanor, so it’s all in the breeding and it's probably because cats absolutely refuse to indulge in any kind of thing other than just using you as a slave and a food machine. What do you think Patrick, you’re the geneticist. Is there a genetic reason why cats don’t behave?
Patrick - I'm familiar with how dogs became domesticated to some extent. There's I suppose some kind of cooperation between humans and wolves and ultimate domestication but I don't know how cats became domesticated.
Chris - Perhaps the Egyptians had something to do with it. They loved cats didn't they?
帕特里克-。但是原件big cat that they took and made into a small, friendly cat?
49:27 - Biodegrading plastic
Biodegrading plastic
Chris put Stephen's question to chemist Ljiljana Fruk...
Ljiljana -Yeah. So people are actually still working on all kinds of polymers and biodegradable polymers are a big thing. And there are lots of procedures out there to turn some of the natural polymers like cellulose is a natural polymer, or chitin - present in the shell of shellfish and in insects - is also a polymer that has been used to make some biodegradable polymers as well.
But I would like to point out here that maybe the biggest problem when we think about plastics is not design of biodegradable plastics in itself, because the industry and also the applications of the plastic. The industry will always look for processes which are cheaper and for now we have plastics and polymers which are way cheaper than biodegradable plastics. So maybe instead of also only focusing on biodegradable plastics, we also need to focus on finding the ways how do we recycle the plastics that we already have out there in the environment and how can we reuse it for something else? And I think this is more a question of the policy than the science.
Chris - And this question about when these things break down, what they break down into?
Ljiljana -Yeah well the problem is - OK biodegradable plastics that will all depend on what is it made of? And so polylactic acid for example is biodegradable, so it wouldn't be as terrible as one would imagine. But you would still have a very persisting big parts of plastics which might end up in the stomachs of animals and then go through the system. We are still not out there that we could definitely find the biodegradable replacement for the plastic that already exists.
Chris - It's a good point though isn't something that in this era we need to focus on finding things that we know will not just rob Peter to pay Paul, because it's easy to brush this particular plastic waste under the carpet isn't it? And say “well it's biodegradable now” but you know what it turns into is pretty important.
Ljiljana -Exactly so I think more focus should be done first on how do we deal with plastic waste and replace types of plastic that are already there. We are not just going to stop making them. And the second thing, could we may be taking cues from the real bio-polymers like as I said so cellulose and chitin which have natural mechanisms of breaking down. So I think this will be the direction that science will focus in the future and it's focusing now as well.
52:31 - How far is a light-year?
How far is a light-year?
Chris Smith put Emily's question to astronomer Carolin Crawford...
Carolin - Even though it sounds like it ought to be a measure of time, a light year is a measure of distance.
So it's how far light travels in one year, and we all know that light has a finite speed: it’s the fastest thing there is. It travels at 300 thousand kilometers per second but that means in a year it travels nine and a half million million kilometres. And astronomers kind of get fed up saying millions and millions and millions! So we just stick to light years. So therefore a light year is telling you a distance that it takes light to travel in one year.
So, getting back to your question, you've got your aliens or whatever a hundred million light years away. The light that they receive in their telescope that’s come from the earth, has taken 100 million years to get to them. So they are just seeing the light that left Earth a hundred million years ago, so they're seeing the Earth as it was a hundred million years ago.
So you're exactly right about that. And this is such a neat thing for astronomers though, because it does mean that we can effectively look back in the past because we can compare a galaxy that's, you know, 100 million light years away to a galaxy that 6 billion light years away and we're seeing the universe at different epochs so it does work in our favour at times.
Comments
Add a comment