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Naked Scientists episode

Sun, 9th May 2010

Does Beer Kill Brain Cells?

A glass of Wheat beer (c) Trexer at Wikipedia

Is there a cure for spots?  Why do we cry?  Does alcohol really kill brain cells?  It's a Question and Answer Extravaganza on this week's Naked Scientists!  We find out what makes a Chameleon change colour, why birds fly into windows and how a hair can change colour along it's length.  Also, witnessing the birth of stars, the Neanderthal genome and how washing your hands can change the way you think.  Plus, Meera dabbles with green gadgets and smell-free toilets in the home of the future, and Dave shows you how to build a hovercraft in Kitchen Science.

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In this edition of Naked Scientists

Full Transcript

  • 01:35 - Herschel sees super-massive stars forming

    The recently-launched Herschel space telescope has revealed a new way in which massive stars might form - at points where supersonic shockwaves hit clouds of dust and gas.

  • 03:53 - Meet our Neanderthal ancestors

    This week has seen the sequencing of the Neanderthal genome, which helps to answer some puzzles - did humans and Neanderthals ever mate? How many genes do we share..?

  • 06:56 - Wash your hands, wash away doubt

    Pontius Pilate is probably the most famous person to have washed his hands of a problem, but new research suggests that the act goes beyond just the metaphorical: scientists in the US have found that washing hands can alter the decisions we make about something subsequently!

  • 09:48 - Taking photos through opaque objects

    Something which has always tantalised many people ranging from surveillance agencies to the more dubious parts of society is being able to see through opaque objects...

  • 11:27 - Untangling triple negative breast cancer

    New work led by Cancer Research UK researchers have discovered why some cancers may be resistant to chemotherapy and radiotherapy – as well as an intriguing link to the breast cancer gene BRCA1...

  • 15:13 - Deciphering the Second Genetic Code

    Researchers in Toronto and in Cambridge have made a major breakthrough in understanding how DNA works. More specifically, how the same gene can produce different gene products in different types of cells...

  • 25:06 - Why haven't scientists been able to create life in the lab

    Perhaps a meteorite crashed into the earth and combined with terrestrial material and gases to kick start simple forms of life.  Given how much we know about microbes and their DNA and chemical content, why haven't scientists been able to create simple living organism from scratc...

  • 28:02 - How and why do chameleons change colour?

    I've always thought, like many of my students, that chameleons change colour in response to their environment.  However, after doing some research it seems they change colour based on temperature, light intensity, and mood.  If this is true how does the colour change always seem ...

  • 31:14 - Would you feel lightning strike a house?

    I was woken up last night by the loud sound of thunder and I swear that I felt the house shake. We live on the top floor of a condo complex. Is it possible to feel lightning strike the house? 

  • 32:46 - Why do birds fly into windows?

    I have had a bird sitting on my deck ledge and he keeps flying off the ledge and right into my kitchen window over and over and over again.  He has been doing this non-stop for 2 days now.  What is wrong with this bird?

  • 34:45 - Does alcohol kill brain cells?

    My friend and I were having a discussion the other night and we wondered if there’s any truth in that common statement that alcohol causes brain cell death what the measurable effect is. Her partner also said that spicy food also kills brain cells, we wonder if there is any trut...

  • 38:22 - Grand Designs Live - Greener Technology for your home

    Meera explored Grand Designs Live at London's Excel centre to find greener ways to fill your home with gadgets...

  • 51:16 - Why do we cry?

    Why do we cry? What it it's purpose and how has it evolved in humans? Why do some people laugh and cry at the same time? Is it also possible to biochemically distinguish crocodile tears from real tears?

  • 53:24 - Is there a cure for spots?

    Why do we have spots and some people have acne and others don't? Is there a possible cure?

  • 57:56 - Why haven't crocodiles changed?

    My question is about the stability of change with crocodiles. We learned from various sources that all birds, incredible varieties of birds, came from a small pool of dinosaurs and mammals apparently all came from a shrew-like creature. I just wondered why crocodiles seem to be...

 

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How can we see through such an amorphous material as glass. If it were a crystalline solid, I could see the solution, but a randomly structured material like glass? Surely it should be like looking through cheap plastic windows. But it isn't. Why not? johnmuir, Sun, 9th May 2010

Hi John

I'm not sure I can understand the problem - can you explain in slightly more detail?

Chris chris, Tue, 11th May 2010

Hi Chris,

Why don't the photons get scattered randomly as with an opaque material, such as plastic sheeting, resulting in not being able to see an image on the other side? Glass is an amorphic solid isn't it? The textbook diagrams liken refraction to rows of photons all slowing down in the material and speeding up again when exiting the material. But why don't the rows get scattered when encountering the material. Generally, what is the feature that distinguishes transparent material from opaque material? (Have I explained that clearly enough?)

John johnmuir, Thu, 13th May 2010

Hi John

Thanks for the clarification.

One way to look at this problem is to compare liquid water and snow. Both are molecularly identical and composed of H2O, but one is opaque - and highly reflective - the other transparent. You could also consider a bucket of water into which you tip a capful of Dettol, making the water go white.

The reason for these opaque, reflective effects (snow and dettol) is down to the particle size. In snow, when light passes from the air into the ice crystals it slows down and refracts (bends). Leaving the ice again the light re-enters air and bends / refracts again. Done enough times - because there are many particles surrounded by air - this has the effect of returning to your eye all the wavelengths of light so you see a brilliant white surface.

But liquid water does not behave in this way because it is not individual particles surrounded by air; the optical density / refractive index of the medium is therefore relatively homogeneous, so the light is not refracted multiple times and so you can see through it.

And the dettol in water?

I gave this example to prove my point because dettol in water produces billions of tiny micelles - oily bags. So light passing into the water is continuously passing from water into oil and back into water, refracting with every change of medium. This makes the liquid like the snow crystals and it returns all wavelengths to your eye, making the water look white.

So, to summarise, a white, opaque surface - like titanium-based paint - refracts the light hitting it to the extent that all wavelengths are returned to your eye, making the surface look white. A transparent substance does not cause multiple refractions like this and so you can see what is on the other side of it. But because it does refract the light a bit - as it goes in and out - light passing through is bent and so your eye can perceive where the transparent material is; otherwise it would look invisible. Dave has an excellent demonstration of this as a kitchen science in which he immerses a pyrex bowl in cooking oil. As the refractive index of oil and pyrex is nearly identical, the immersed bowl vanishes!

Chris chris, Thu, 13th May 2010

Hi Chris,

Thank you, that's a very good explanation for the effects at the microscopic level, but I'm really trying to understand it at the level of a single photon. What exactly happens when an individual photon encounters materials such as diamond and glass. With diamond I could see that the regular lattice structure allows the photon to, as it were, pass down the tunnels in the lattice without interacting much with the individual atoms (does it?). But with an amorphic solid such as glass, surely it would be randomly scattered by an atomic nucleus within a few nanometers. It isn't, but why not?

Or does it have anything to do with the inter-atomic separations and the probability of an individual photon being scattered by a nucleus? But that surely can't be the explanation either, as a photon isn't a neutrino.

A puzzled John... johnmuir, Fri, 14th May 2010

Hi John

You have to remember that photons can behave both as discrete particles (as in the photoelectric effect) and also as waves (as in diffraction); it's probably therefore unhelpful to try to consider particles fitting through holes in a substance.

The bottom line is that light is an electromagnetic wave; when it interacts with a substance the electrons in that substance soak up the energy in the light wave and then re-release the energy, re-generating the light wave. This happens sequentially as the "light" passes through the material, with electrons handing on the energy from one to the next. At a simple level, this process takes time, which is why light travels more slowly in a more optically-dense (higher refractive index) substance.

Chris chris, Sun, 16th May 2010

Hi Chris,

OK I'm thinking about cats... Your explanation makes sense but applies to any material, whether opaque or transparent. Is the difference between them the energy required to raise the energy level of an electron in the outer ring... transparent = little, opaque = a lot?

If I assume that in glass a (visible wavelength) photon contains just the right amount of energy to raise an electron to a higher energy level and that within a short space of time it decays again re-emitting a photon, then why do the photons travel in a straight line in glass? Is it due to the conservation of momentum? Or is there another explanation?

And what (once again) is the difference between opaque° and transparent substances that dissipates the photons in opaque substances, but allows them to travel in straight lines in transparent ones? The conservation of momentum solution applies, after all, to all substances, so that seems to rule it out, at least as the complete solution.

John

PS° For 'opaque' use e.g. plastic sheeting, as that allows the photons to pass through, but not in straight lines. johnmuir, Mon, 17th May 2010

Hi John

Remember that "transparent" and "opaque" apply to a substance only in terms of the wavelength of the light you are dealing with.

For instance, microwaves and visible light are both "light", but the grille on the door of a microwave oven is opaque to microwaves - to protect the user - but transparent to visible light, which can still exit allowing you to see the food cooking inside.

The reason is that the wavelength of visible light is a fraction of the wavelength of the microwaves, which are impeded by the metallic grille. The visible light, however, slips through the gaps in the metallic mask quite easily.

Conversely, mobile phone signals travel quite nicely through the walls of houses, but visible light doesn't.

As a visual demonstration of this, for Kitchen Science, Dave has turned a webcam into an infrared camera; pointed at an apparently opaque, black bottle of Coke, this IR camera sees straight through as though the Coke is colourless.

Chris chris, Tue, 18th May 2010

Hi Chris,

That's it! Many thanks for taking so much trouble about this.

John johnmuir, Tue, 18th May 2010

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