Q and A: Disney, Dark Matter and Deja Vu

Neuroscientist Philipe Bujold was asked this question from Marika by Chris Smith, and told us all some theories about déjà vu...

Philipe - I’ve had that question a few times. Actually, unfortunately, I can’t give you a hundred percent certain answer because we still don’t know what a deja-vu actually is. We have a few theories though and that involves a lot of the memory circuits. The hippocampus is involved in encoding the context in which memories are formed but right next to that there is a part of the cortex called the rhinal cortex. And that rhinal cortex is divided, but it’s main role would be to recognise what’s familiar. And so one of the big theories at the moment is that this rhinal cortex needs to fire inline with the hippocampus, which encodes context, and then that opens up a memory, so it will fire the network that’s associated with the specific memory. If, unfortunately, you don’t have that context firing, you just have that feeling of familiarity, then that might be why you have a deja-vu. So we’re not sure. The only really studies that have been done into that are starting to show us that that’s the case. The stimulation of these parts of the brain that also seem to create fake deja-vus, if you want, but we still don’t know why it would happen. It seems to happen more in young people, or it might just be that young people are more aware of it because we still have a lot of our brain intact because ageing hasn’t started.

Chris - It happens to me when I’m tired. Does that make a difference?

Philipe - Yes. So stress and fatigue actually are huge links to more deja-vu experiences.

Chris - I suddenly have a sort of flash or recollection and a feeling of oh, I’ve thought of this before and it’s a memory that’s fleeting. It’s there and then it’s gone and I can’t get it back. But it only happens when I’m really tired. After night shifts and things when I was a junior doctor, it would happen quite a bit.

Philipe - Yeah, exactly. So that’s probably when it would happen, especially for undergrads actually. I think it’s something like two thirds of undergrads seem to have experienced a deja-vu feeling.

Chris - Oh, don’t remind me.

Chris - Fran?

弗兰,我绝对相信当我佤邦s seven or eight that a deja-vu was something that I’d dreamt but I’d forgotten the dream, so I was sort of remembering from a dream. Is that at all plausible?

Philipe - I wish I could give you an answer. I don’t actually know. I would not think so because our brain seems to be very adapted to not remembering dreams otherwise we would have a lot of issues functioning in daily life. You already have to remember what’s happening for 12 to 16 hours every day, if you have to remember everything that’s happened overnight also that would be a big issue.

Chris - There are some people that do though aren’t there? These people who have some kind of savantic behaviour and can remember an excruciating episodic detail everything that’s happened to them throughout their lives.

Philipe - Yes. So it does happen for some people. That is fortunately not the norm because it is, like you said, excruciating for these people, but it happens in some cases. I wouldn’t be able to tell you why it happens but it does happen, yes.

Chris Smith asked Deirdre's question about how lasers work to materials physicist Jess Wade, who shined a light on the topic...

Jess - Oh, this is a great question Deirdre. Everyone loves lasers right, along with slime. They’re the second best thing in physics. Lasers work because we have atoms and inside an atom are some protons and neutrons, which is what Fran studies. We’re more interested in the electrons in material science, and what we need to do is in a laser is we need to excite one of these little electrons up to kind of excited state we call it, but it’s really unstable in this excited state. It’s like you give a child loads of slime to play with and they suddenly go ferociously energetic.

Chris - Loads of sweets!

Jess - And then really quickly it needs to stabilise, so it emits some light to get back down to its ground state. And you can do a really clever thing where you trap loads of atoms together so that when that one little electron jumps down and emits its light it excites another electron that’s nearby it and makes that emit its light also. And you have this kind of cascade affect where it keeps happening and you can do that by trapping these atoms between mirrors or something clever. What’s really exciting about laser light and why physicists like it so much is that little jump that the electron makes. That energy that it gives out is really specific to the atoms that you’re exciting. So laser light is only one colour, it’s only one energy and that lets us do all kinds of clever physics because we can then use that laser light to excite different atoms which absorb that particular energy, and it’s also super focused. You get these laser beams. You have a light bulb that gives out this really diffuse light but laser beams come at super focused, and we can keep them focused for a very very long time.

Chris - And, of course, by using different flavours of atoms you can get different colours of light that have different applications. Because if you want to do say medical imaging or you want to burn bits of tissue, you want a laser that will interact very well with tissue but not other things?

Jess - Exactly. And it’s very similar to fluorescence. So fluorescence is this thing where we excite an atom and very quickly they emit light and it happens over a very short timescale, and when it happens it’s gone. You can tune that fluorescence, you can tune that colour to whatever atoms that you are exciting.

Chris - Eleanor?

Eleanor - So talking of applications, something I’ve always wondered about lasers, taking this to a really highbrow level, I love Star Wars and one of the weapons they use is this kind of laser shooters. Is that ever going to be possible having kind of weapons that are lasers?

Chris - Do you have nefarious intent or something?

Eleanor - Of course not. I don’t know why you would suggest that.

Chris - When working with the ants becomes too much.

Eleanor - Well, you know.

Chris - It’s gone from burning them with a magnifying glass to a laser blaster!

Eleanor - I would never do that.

Chris - A laser blaster. Jess?

杰斯-如果你想要一个激光光束a laser blaster, right. If you get a very powerful laser you could fire it at something. You can pop balloons with certain lasers. You could certainly blind yourself with a laser. The majority of time spent at the beginning of your PhD in materials is trying to complete laser safety courses so you don’t blind any of your friends with a laser. So I don’t think you’re far off the Star Wars thing if you want one.

Val wanted to know why some metals rust faster than others, so Chris Smith put the question to materials physicist Jess Wade...

Jess - The technical term I think is corrode. Rust we only think about iron so iron rusts and goes that typical kind of rusty, bronze colour so that’s right. And corrode is when metals interact with oxygen, usually in the presence of water, and it’s because oxygen is super reactive; the oxygen that’s in the air. It’s a really hungry little gas. It needs to fill two electron spaces so it attacks these metals, which are kind of seas of electrons, and tries to pull them off that to react with it.

In some metals this seems to happen very quickly, so in things like iron. The interesting ones are the things where it doesn’t happen and aluminium actually super quickly, aluminum that we use in cans and in an awful lot of products, covers itself with a very very strong layer of aluminium oxide so that makes it look like its not rusted, but that layer is super tough and sturdy and no more oxygen can get through it. So we can do that.

我们可以用金属做其他类型的聪明的事情where we blend them with other metals to stop them from corroding. I think the ones that are really interesting are things like gold and platinum, which have this sea of electrons. You know gold is really good at conducting electricity, which is why we use it so often and it’s beautiful if you buy expensive jewellry. But that doesn’t seem to rust, so the kind of interesting questions are why is that not happening? And I think that’s much much more complicated than we think. It’s a kind of quantum chemistry question why it doesn’t happen in gold.

But certainly all metals do seem to rust. They want to get back to their kind of state where we found them in these mountains and when we started refining them in the first place. So it’s a rate: you can look at a table to see which will rust faster.

Chris - You can make gold dissolve, but you need a mixture of all of the three sort of king acids, don’t you? Nitric, sulphuric and hydrochloric acid. Aquarega I think isn’t it to dissolve gold and it’s pretty horrible stuff?

Jess - Yeah. I don’t advise doing that at home.

詹姆斯想知道为什么蜜蜂刺死you, but wasps don't. So Chris put the question to animal behaviour expert Eleanor Drinkwater...

埃莉诺-这是一个很好的问题。我最近ly started beekeeping so this is a question that we’ve been particularly interested in. But the answer…

Chris - Are the bees faring better than your ants?

Eleanor - Yes, they’re doing marvellously.

Chris - Are you putting RFID tags on them?

Eleanor - No, no, no. We’re looking after them brilliantly. They’re doing really well. They’re excellent. I’m very proud of them all.

Chris - So the bee proud of you.

Eleanor - Yeah, exactly. They are amazing. So what you're talking about is the fact that honey bees, in particular - there’s many types of bees but I’m guessing that in this case we’re talking about honey bees, they have a barbed sting. So if they sting something like a mammal that’s got nice fibrous tissues then they will actually pull out… If they stick their barb in it will get stuck, and so then if the bee is removed quickly, then it will pull out the sting and quite a lot of associated tissue as well, so they effectively disembowel themselves, which is quite sad. But the amazing thing about it is they can still live to - I think the study said up to 114 hours after effectively disemboweling themselves.

Chris - Why have they evolved to do that though? Because Australian native bees don’t have barbs. They are stingless. They’re barbless.

Eleanor - This is the honey bees particularly. I was reading about this to try and answer this question because I thought that might come up, and there seems to be two schools of thought. One of which is suggesting that perhaps it’s maladaptive and it’s just that it was evolved to sting other insects which don’t have the fibrous tissues like we have.

The other school of thought, which I think I prefer, is the idea that if they have the sting in longer in causes maximum amount of damage to the mammal. Because there whole time it’s pumping the venom into the mammal and so, essentially, the worker is sacrificing herself for the colony. Then the fact that they can survive for up to 114 hours after they can still participate and help defend the colony.

Chris - So it’s all in the name of better persuasion against nest raiding.

Eleanor - Well, that’s one hypothesis. Obviously, it’s quite hard to…

Chris - You may not know this but do furry animal fare better? As in do bees manage to find it harder to sting things like dogs and bears and things that might go after their nest because they go to the exposed parts on us? My brother, who keeps bees, told me that when his bees get into your hair, because we watched a swarm arrive at a capture hive he’d set up the other day and we had them all buzzing round us, he said just watch out if they get in your hair because the tend to panic when they get in your hair and then they just sting you. None did sting us but do furry things fare better - or fur better?

Eleanor - I don’t know. I would guess it would probably depend on the type of fur. Because I guess if you could get like our hair, if you get tangled in it you’d have someone panicking. But I would wonder whether on other animals, the fur is kind of thick enough that you can’t sting through, like us wearing our beekeeping suits.

Dan wanted to know what quantum entanglement was, so Chris Smith put the question to physicist Francesca Day...

Fran - Quantum mechanics describes the physics of how very small things work. And it turns out that the physics of how very small things work is super weird, and nothing like the physics of how everyday objects work. And one important point is that in quantum mechanics nothing is decided until we measure it.

Chris - Can I just clarify, when you say really small stuff, how small is really small?

Fran - The size of an atom or an electron, or a proton which are the particles in atoms.

Chris - Does that mean then if I could with a microscope start with something big and watch how it behaves, and get smaller and smaller and smaller and see progressively smaller things I would suddenly, at some point, see the behaviour switching and going into this quantum realm where things behave totally differently than bigger objects?

Fran - That’s a very interesting question whether you could do it gradually. No-one quite knows how the transition from quantum to classical physics works. It’s one of the really open mysteries because there isn’t a microscope that can do that whole range.

Chris - Ah. So quantum mechanics has thought of that and caught us out?

Fran - Yes. Quantum mechanics is very good at doing that kind of little trick.

Chris - Because Niels Bohr said if you’re not baffled by it you didn’t understand it, didn’t he? He’s saying look, you know I understand how it works, I understand the results I get but I don’t understand why I get?

Fran - That’s absolutely right. Quantum mechanics is a set of rules that’s very very good at predicting the results of experiments. So you have to sort of go with it but…

Chris - And just abandon all hope of actually understanding why? You just know it works?

Fran - We haven’t abandoned all hope. There’s a lot of scientists working on it.

Chris - Okay. So coming back to this idea of entanglement, what’s that?

Fran - As I said, we don’t decide things in quantum mechanics until we measure them. So, for example, photons which are particles of light have a property called polarisation and that describes the direction their electric field points in. And before we measure the polarisation of a photon, even the photon itself doesn’t know its polarisation.

Now it’s possible in an experiment to have say an atom emit two photons at once such that they have to have their polarisations pointing in opposite directions. When we do this, and say the photons travel to opposite ends of the world and then we measure one of them and it’s pointing in a particular direction. Then we measure the other photon and its polarisation will always be pointing in the opposite direction because those two photons are then entangled, and this happens instantaneously. So it’s very mysterious how the information can travel from our measurement of one photon instantaneously to our measurement of the other photon.

Chris - Now is it that the entanglement, the decision as to what polarity you’re going to have, that decision is made at the moment the two photons leave the atom or is that decision made only at the time when you measure one of them? Do we know?

Fran - It’s made only at the time when you measure one of them.

Chris - And how do you know that?

Fran - From the experiment I’ve described there isn’t a way of knowing that. So you might think well why isn’t it just decided at the source? But there are actually more complicated experiments you can do involving measuring things at different angles, and doing lots of different measurements that show that it has to be decided only at the point of measurement. They’re called Bell Inequalities if anyone wants to google further.

Chris - Over what sorts of scales can this operate? Or is it infinite as in if I had a particle which was generated at the time of the big bang, and another particle its pair, they’re now on opposite sides of the universe. As far as we know does the same rule apply?

Fran - Yes. As far as we know it is infinite. However, when I say a measurement, something like the photon interacting with a few other particles, interacting with its environment can destroy the entanglement. So you’d have to really isolate your photon somehow as it travelled across the universe.

Chris - But that also means that there is, in some way, information travelling over vast distances in zero time for this to hold. So how on earth is that happening?

Fran - We don’t know. It seems like it’s in conflict with Einstein’s theories which say that things can only travel at the speed of light, not infinitely fast. It’s actually possible to prove that it’s not possible to communicate this way in a way that violates Einstein’s theories. But it’s still very mysterious and people spend a long time worrying about it.

Chris - It certainly is. But it could hold the key, well it does hold the key to information protection, doesn’t it? Because basically, it’s a failsafe way of knowing if information has been tampered with if you entangle some information in this way, and you’ve read one bit of information it will change the other so you can tell? And that’s how online security works, isn’t it?

Fran - Yeah. So people are very interested in this for security purposes. It’s a lot better than anything you can do classically because it’s literally tamper proof from the very laws of physics themselves.

Chris Smith put this question to physicist Francesca Day, who definitely didn't keep us in the dark...

Fran - First I should quickly explain what dark matter is in case anyone doesn’t know. Dark matter is matter that we think is there because we can see the effects of it’s gravity on other matter like stars and galaxies in space, but we haven’t detected it any other way than its gravitational effects. So then you might think well, maybe it’s not that there’s extra matter, maybe we just haven’t quite understood gravity. And, indeed, there are physicists that work on modified gravity as an alternative dark matter.

Chris - What’s modified gravity?

Fran - It’s where you take Newton’s laws of gravity or even Einstein’s theory of gravity and you tweak it to try to fit the observations better.

Chris - That’s called fiddling, isn’t it? Isn’t that called adding a fiddle factor to make the observation fit the fact?

Fran - Yes, absolutely.

Chris - It sounds iffy to me.

Fran - Dark matter is much much more popular because based on just having one more particle in our model of particle physics, and having there be some of these particles around we can explain all the observations. But there are observations that dark matter can explain very easily but modified gravity can’t; for example, dark matter is required to explain how structures like galaxies form in the universe in the first place. You need the gravity of the dark matter to be the seed that hold the galaxies together, whereas modified gravity can’t explain this. So dark matter really explains a lot of different astrophysical observations with only one addition, which is what makes it a very appealing theory but, of course until we detect it we can’t know for sure.

Chris - Why would all the dark matter stick together and be in a big halo round a galaxy for example? Because if it’s gravitationally active, why isn’t it all sort of mixed up with the other material we have, the stars and the planets and so on?

Fran - It is, but it’s more the case that the stars and the planets are mixed up with the dark matter. We think that dark matter probably only interacts significantly via gravity and it’s other interactions are very weak, so the dark matter falls in on itself because it’s gravitationally attracted to the other dark matter and forms these big blobs of dark matter.

Chris - So dark matter is attracted by gravity to other dark matter but it doesn’t interact with dark matter in any special way apart from via gravity we think?

Fran - We think. It might interact with other dark matter using some other forces that we don’t know about yet, but there’s no direct evidence for that.

Chris - And we think it was there what as a product of the big bang? Has it been around since the birth of the universe?

Fran - Yes. In the same way that all the regular matter that we see every day was produced in the big bang, dark matter would also be produced in the big bang at the same time.

Chris - So when scientists talk about there being particles of dark matter whizzing through us all the time, one physicists at UCL in London put it to me that if I had a pint glass, I’d have at least a couple of dark matter particles in there right now. Why is that there? Why isn’t it out aggregated around with the dark matter in a halo then? Is that just a reflection on how much dark matter there is all over the place, all the time?

Fran - Yeah. It’s best to think of the Earth as being in a dark matter halo. The Earth is situated in the Milky Way galaxy, and the Milky Way galaxy is situated in a big sphere of dark matter. So because we’re in this big sphere of dark matter there are dark matter particles around everywhere.

Chris - Will the dark matter go where the matter goes? Is that why we’ve got our galaxy, there’s a mixture of matter and dark matter in the same place in space and time?

Fran - Yeah. They’re gravitationally attracted to each other. But it’s better to think of it as the matter going where the dark matter is.

Chris - Philipe?

Philipe - Because dark matter is then a form of matter, would there be something as an anti-dark matter particle?

Fran - That’s a very interesting question. In some theories of dark matter there is anti-dark matter particles but in some theories there aren't. In the same way that an electron has an antiparticle which we the positron, but a photon is its own antiparticle, it doesn’t have a different antiparticle. It’s the same for dark matter, so some dark matter wouldn’t have an antiparticle but some could.