Why does cannabis cause the munchies?

Can we harness the power of the ocean for electricity? Why are some people lucky? Can I stop my plant from fruiting? Why do my eyes go red when I smoke a joint? What's worse for your health, cigarettes or joints? Plus, scientists find a lake on Mars...

Eusebius - Good morning to you Chris!

Chris - The big story this week is that researchers from the Italian Space Agency - this is Roberto Orosei and his colleagues - have discovered what they think is a lake. And by Lake we mean actually physically liquid water on the surface of Mars or at least within the surface of Mars. The way they've done this is to use the European Space Agency's Mars Express probe which is a satellite orbiting Mars. It's equipped with radar and by pinging radar waves off the surface of Mars you can look at the reflections that come back. And different surfaces and different compositions of surface will reflect radar differently and you can use this to tell you what might be in the surface. Now we've known that Mars was a very wet place in the past and still has a lot of water locked up as ice in the surface. We've known that for a really long time, but no one realized they might be physically a body of liquid water there, which is what these researchers claim to have found in the journal Science this week. And what they did was to analyze these radar pictures and see this area, maybe 20 kilometers long down in the Martian equivalent of where we have Antarctica. So the south pole of the planet there is this thin strip which looks like it probably is liquid water. The slight wrinkle here is that it's about a kilometer and a half underground, so it's a long way down. It's not very deep, it's perhaps a metre or so deep, maybe a little bit more. But at these sorts of conditions that it will be in, deep high pressure and Mars is cold as in tens of centigrade below zero, this water must be incredibly salty in order to still be water, but it's still physically liquid water. And so researchers are encouraged by this because we know that liquid water is probably a prerequisite for life. And we know that Mars was a lot wetter and there are environments on Mars in the past which almost certainly could have sustained life if it started there. So as Mars dried out, maybe that life retreated into places like this pool of water that these Italian scientists claim to have found because there are extreme organisms, dubbed extremophiles, which inhabit similarly nasty environments here on Earth and they thrive and flourish in those conditions. So it's not beyond the realms of possibility that if there was life on Mars it could now be loitering and lingering in areas like that one discovered by the Italians this week.

Eusebius - Fasinating. Daniel, good morning.

Daniel - Hi there, good morning.

Eusebius - Go ahead. What's your question for us?

Daniel - Are we able to use to the ocean currents, like the Benguela Current, and put what I would describe as wind turbines under the ocean and harness the electrical power that harnesses basically the flow of the water, the currents to actually power those electrical turbines and create electricity for ourselves.

Chris - So what you're suggesting is would it be possible to put some sort of subsea turbine on the ocean floor, or even floating at some point in the water, and as the movement of the water with tides and currents and so on goes past it would impart some kind of force onto that turbine, turn the turbine and could we extract energy? The answer is yes. People are doing this in a range of ways. The simplest is that you find some appropriate bit of coastline. I mean one example is the west of the UK where there is a funnel effect created by the South of Wales and the north coast of Devon and it forms the River Severn estuary. And water is funneled in there for a very long distance inland. If you build a barricade, then you can let the water in when the tide is coming in and generate electricity in one direction. You let the water out when the tide is going in the other direction. So that's one simple way of doing this. I say simple, it's incredibly expensive. There are ecological and environmental costs as well. But the other thing to do is to say well we also know, as you're alluding to, that the water moves on mass as a current around land masses. So we know that if you look at a marine chart you'll see that the tide is running in a certain direction at certain times of the day and it's strongest in certain places. So could we extract energy from that too? Scientists are looking at this. There are various companies that are making subsea turbines. The problem with them is anchoring them to the seabed - that can be tricky. But there are ways of doing this and so they have very big - you tend to make them big because if you make them small they have to turn very quickly. If you make them big you can have a very slow turning propeller or impeller, and this means that actually you do less damage, because you don't chop up fish and things, but also it means there's less turbulence, so you waste less energy. So they are doing this. It's difficult to do; it's difficult to maintain these devices, and it's tricky whether or not it really does make a lot of environmental sense because the infrastructure is so demanding. Putting them in, maintaining them, recovering the energy - the electricity - from these things, but it can be done and people are actually doing it. I saw Rolls-Royce actually were working with the company that were developing these things because I think they were making the blades for them. So I've seen pictures of them and they're talking about using them around the coast of Scotland as well because there are some strong currents that run there. So it's a good idea; people are actively pursuing it.

Eusebius -Great question. Thank you Daniel. Andy, good morning.

Andy - Good morning, Dr Chris. It's Andy here from Boksburg. I am a bridge player, the card game bridge, and I just would like to know what determines luck? Why are some people lucky and other people are unlucky? Is there some kind of scientific explanation?

Chris - Which are you?

Andy - Which am I? I'm unlucky.

Eudebius - I'm unlucky with the lottery as well so I've got a vested interest in this question.

Chris - It's okay to be unlucky as long as you're consistently unlucky and then you can always bet on what you think you are not going to achieve. And so you're at least consistently and nothing else. Some people say they don't believe in luck. Some people say, in fact Rick Wakeman said in his book "Say Yes!" he wrote, "I don't believe in luck, I think it's where opportunity meets preparation". I'm a great subscriber to that. I think that you make your own luck and to a certain extent there is chance. But I think you make your own luck by being prepared and assimilating all of the information and deploying that information in the right way, at the right time, when an opportunity arises. So in other words it's knowledge largely, but it's putting yourself in the right place at the right time and that is something that you can anticipate. And then there is the coin toss that occasionally happens. But I think on the whole you can anticipate a lot of things and you shift the balance of probability in your favour if you can.

Eusebius - What about things like subatomic particles, don't behaving in random ways?

Chris - Well, we discussed this on the programme previously didn't we when we're talking about Schrödinger's cat? Because Schrödinger was uncomfortable with the concept of quantum physics and said well okay, I'll dream up this experiment. I'll have a cat in a box, and what you're telling me is that the cat is either both alive and dead all at the same time. So what I'm going to do is I'm going to have a cat in a box with a radioactive source. And the radioactive source when it fires off a particle, if the Geiger counter detects that particle it causes a hammer to crack a vial of cyanide and that will kill the cat. So what you're saying to me is that the cat is alive and dead at the same time until you open the box and decide its fate, and everyone said yeah, that's fine. And Schrödinger said "I'm not comfortable with that", and Einstein said "I'm not comfortable with that either!" But the luck is something slightly different, which is people say I was lucky that I wasn't killed in that car crash or I was lucky to win the lottery. But actually what we're doing is we're attaching significance to coincidence. Coincidentally the outcome was one which we hoped for or which was in our favour. So we therefore say "oh, it must have been because of X, Y and Z." And, actually it happened 99 times out of 100 before that not in your favour, but you just thought ah well you know, that's the way it is and ignored.

Eusebius - John, good morning.

John - My question is how can I stop a black mulberry tree from fruiting? I like the tree but I would like to stop it from fruiting!

Eusebius - There is irritating dark little berries!

Chris - Yeah it's a tricky one. I don't know a simple solution apart from cut the thing down which is, obviously, not a very green answer is it?

Eusebius - Is there a biological way to stop it with any kind of fruit?

Chris - Well, kill it! That's the usual way of biologically stopping something from doing something is to kill it. But that's not the ideal solution because we want to be environmentally friendly on this show. I don't know how you can stop. I don't know if there's a simple nice kind environmentally friendly way to stop a tree fruiting. I think the only solution would be to distance yourself from it, which would leave it alone, and leave you alone, and everyone's a winner.

Eusebius - Leah, good morning.

Leah - Good morning. My question is I noticed that in the summer the Sun seems be at a higher pitch or the Earth at a different pitch because when the sun comes into my lounge it comes in at a different angle. In the winter it seems to be lower. I just want to know if there is a shift either in the Sun or the Earth?

Chris - Hiya. What an interesting question.答案是肯定的。地球是倾斜的。如果你imagine the Earth as a bit like a tennis ball or an orange or an apple or something, and imagine that you've put your finger and thumb - you're holding it at the top and bottom of the orange. If you twist your hand one way or the other twenty three and a half degrees, so that your finger and thumb are pointing just slightly off of the top to bottom, that's roughly the inclination of the Earth - twenty three and a half degrees. And it goes round the Sun in a giant circle tilted like that. Now that tilt doesn't change but, of course, as you go around the Sun you're going to be either facing your half of the planet in the southern or northern hemisphere accordingly, either towards the Sun on one side of its orbit, or away from the Sun on the other side of the orbit. And that has the effect of meaning that the Sun rises and falls to a greater or lower height in the sky at each time of day at different times of the year. So that's why the Sun is coming in through your window at a slightly different angle at certain times of the year. And it's why old monuments, like those things built in South America; Stonehenge, they were built as sundials as it were, and the Sun at a certain time of year is at a certain angle to illuminate those things in a certain way. And the ancients knew this and they built their things and their stone circles and things to take advantage of that effect because they knew the Sun had a different position in the sky relative to the to the Earth's orbit or owing to the difference in the Earth's orbit as the seasons progress. And that's why we have seasons at the same time.

Eusebius - Speaking of bottoms. Percy, what is your question?

Percy - Yeah hi. Good morning.

Eusebius - Go ahead.

Percy - My question is why is your piriformis muscle in your buttocks and your bum when it swollen it touches your sciatic nerve and then it becomes painful. I'm just wondering is there any solution for that?

Chris - Just before I answer that, Eusebius, did you call him a bottom? Because you said "talking of bottoms" and then introduced him to the programme! It's not very nice way to treat your listeners!

Eusebius - A coincidence.

Chris - Okay. I guess are you a victim, Percy, of sciatica? Is that what you're saying?

Percy - Yes.

克里斯,有一系列的原因我们有科学atica. People who have sciatica complain of pain in the distribution of the sciatic nerve. The sciatic nerve comes out of the lumbar and lumbar sacral vertebrae, or levels at the bottom of your spinal cord, and it comes out through narrow gaps between the bones. And then these nerve roots coalesce to form this big nerve bundle, which it's pretty big, it's the diameter of your thumb, and it runs down the back of your leg and it supply sensation and other things into the back of your leg and down into your foot. And when anything presses on the origin of that nerve, it can cause pain to be experienced in the distribution of that nerve. So in other words you haven't got pain in your foot, but because that nerve supplies your foot or the back of your leg, you will feel pain in that distribution because the body interprets the fact that nerve is being tweaked that there must be something wrong from where those, or from whence those fibres originate in the skin. That's not the case of course, it's because you have a structural problem in your back. Anything that presses on the nerve, therefore, can cause that to happen. Either it will cause the nerve to fire off impulses that it shouldn't and you feel sensations that are not really there - sort of phantom sensations or, in the worst case, if you completely squash the nerve then you can cut off the flow of information, you get numbness, and you can also get weakness in the distribution of nerve. So anything that does that will make that happen. So whether that's because you've had some physical trauma, whether because you've got a disk between the vertebrae in your back which has become deformed and it's bulging and squeezing on the nerve, or you have some arthritis and you've built up a bit of a bony prominence which is pressing against the nerve. All these things can do this. It's not just that a muscle does something wrong it's anything that gets onto that nerve and can squeeze it, and this doesn't just have to be the sciatic nerve. The same thing can happen in other places in the body. Classically if people get neck arthritis in their upper neck, they can squeeze on the nerves that come out and supply your arms and people get numbness and tingling and pain in their arms at times as well. So it's the same sort of phenomenon but in the upper limb.

Eusebius - Jack, welcome to the show. What is your question?

Jack - Hi. Two quick ones Eusebius. How did the Naked Scientists come by that name Naked Scientists? But what I really want to know is when you stand at - well when I stand at the beach and I look away into the sea the water seems to rise as you look further away into the horizon. So is it just me or is there a scientific explanation for that?

Chris - Okay. So taking the two questions: the Naked Scientist was born in 2000-2001 and I've been making science radio programs and podcasts. We were one of the first podcasts ever to exist actually at that time, but we were calling the program something else. And when I launched a new series of it ,and we put it online as well I thought we need a sexier name, and we need something that will make people laugh and then think. Something memorable. Something that does what it says on the tin. But also something that says no barriers broadcasting. And the idea is it's not us, thank goodness, that are the naked ones, it's the science that's naked. But the name kind of works so we stuck with it.

Eusebius - It certainly does. Love the name.

Chris - Oh good. Thank you for that endorsement Eusebius. I'll treasure that. Now in terms of the horizon and how that all works. The planet, of course, is a ball - it's round - and that means if you stand on the beach and look outwards away from yourself then what you're seeing is that you're seeing over the edge of the ball out into what would be space, and that's why the sky appears to come down towards the water because the water is curved around the ball and you can no longer see it. And the evidence for that is if you sail on a ship and you sail away from the shore, the ship will appear to disappear over the horizon until only the uppermost parts are visible and then the ship disappears completely. It hasn't sunk. It's gone over the curvature of the Earth and the sky's come down to meet it. Now when there are waves superimposed on the surface of the water, then those waves when they're further away from shore are smaller, and as they get closer to the shore and the water's shallower they heap up and become taller relative to you, but you're still going to see those movements out into the distance. So that's why the ocean surface appears to be rising and falling. It's the swell which is smaller but still there further off into the distance and you're seeing that relative to the to the horizon. So I think that's why it appears to be rising and falling in the way you describe for yourself.

Eusebius - Leane in Cape Town. There's a very Cape Town question.

Leane - Why do your eyes go red when you get the munchies when you smoke a joint?

Chris - Oh dear, oh dear. We wouldn't advocate anyone should smoke joints of anything on this program. But for those people that might have...

Eusebius - Lo and behold if anyone should open the doors of perception.

Chris - Yes. But if anyone has experienced this, or anyone who wants to know why someone who does this might experience those sensations, then the reason is as follows. There are two things: the chemicals that are in marijuana have an effect on a part of the brain called the hypothalamus where there are nerve cells in there which have cannabinoid receptors. And these cannabinoid receptors, they're chemical docking stations that recognize the molecules which are in cannabis and when they are engaged it stimulates hunger circuits and it makes you want to eat. And these circuits normally play an important role in energy balance and also in making sure that you have, when you have the opportunity, you eat enough and you eat enough food that will keep you at the right body weight. So when you smoke a joint you are subverting this system of energy balance and you're putting it into overdrive, which makes you feel very hungry and that's why people tend to binge and they tend to binge on high calorie foodstuffs when they get the marijuana munchies. The other thing that happens; you mention about red eyes. The other thing that happens is that these chemicals are also so-called Vasoactive. They can change the way blood flows around the body. They can change the way blood vessels open and close. And the blood vessels supplying some of your superficial tissues can be opened and the blood flow augmented. That's one of the things. The other aspect is smoke is very irritant to your eyes. And so when you're smoking the smoke will get onto the surface of the eye it will irritate, and anything that's irritant causes a low level of inflammation and inflammation also opens up blood vessels. So you're opening up the blood vessels in your eyes to flush away the damage that's been done to the tissue superficially where the smoke particles have come into contact with the tissue and irritated it.

Eusebius - Chris, do you have a scientific view on which is worse if you have the same quantities over a period of time for the body - cigarettes or joints?

Chris - Well people have studied the chemicals that are in marijuana and, in fact, it's far worse for your lungs than just plain tobacco. They've done comparative studies where they've looked at the lungs of individuals who smoke just tobacco and individuals who smoke marijuana, and the lung ageing effect of tobacco plus marijuana is significantly worse than the lung ageing effect of tobacco alone. Both are bad. Both have a very severe consequence for your lungs but the marijuana has an augmented effect. And in fact it adds many more years. You have to smoke an enormous amount more of just plain tobacco to get the equivalent damage. This is because Marijuana is very oily and there are lots of other chemicals that come off that are powerfully irritant to the airways, which is why smoking it's not a good idea.

优西比乌-好吧。我们挤在一个最终question for today. Johnny Shane you've been holding on for 20 minutes what is your question for Chris?

约翰尼,我的问题是我70岁了,I have a resting heart rate of 55 beats per minute. When I'm on a mountain bike that's spikes to a hundred and eighty five or a hundred ninety for about two or three minutes, two or three times during the ride which I do twice a week. Is that stupid? Am I being stupid?

Chris - I think it's amazing. I don't think I could do that. My resting pulse is not 55. That's amazing, and the fact is that what you are able to achieve you're clearly very fit because you're able to do a nice low heart rate normally, which means you've got a big healthy heart which is moving a lot of blood with a single beat which is why it doesn't have to beat so often, but it's also got the capacity to run nice and hard and fast when you are exercising. I mean you should take exercise within what you're capable of, and if you start to get any symptoms or you're not feeling well when you're doing this obviously you've got to be careful. But if you're feeling fine then who am I to tell you not to do that. I mean exercise is far better than any pill any doctor can ever give you. I'd say keep it up.

Eusebius - Thank you Chris. I thoroughly enjoy today's installment. We'll do it again.

Chris - Thanks Eusebius. See you soon everyone. Bye bye!