How does the sun produce photons?

How does the sun produce photons?

The surface of the Sun is very hot of course. It’s so hot that hydrogen becomes ionised into plasma so that you have photons and electrons as separate bodies, rather than bound together into atoms. And as those different charges interact, they exchange energy at the surface of the Sun and in the process of saving energy, they can lose energy and that is radiated as the photons that we see. Now that's not actually the powerhouse that drives luminosity of the Sun. That is the fusion of hydrogen atoms into helium which occurs at the core of the Sun. In fact, only in the central 20% or so of the Sun and so, you have another process which is convection which is carrying that heat which is generated at the centre of the sun out of the surface to keep the surface hot so that it continues to shine.

Are there no photons being produced deep inside the Sun? Presumably there are, but they just can't get out.

Photons are being produced all throughout the Sun, but the Sun is made of a cloudy material because these protons and electrons can interact with that light. And that means the photons produced deep down can only actually travel a few centimetres before they're reabsorbed.

And of course Bryan Fulton who was on this program, he’s professor of Astrophysics at the University of York. I think the point he made was that the photons that get made in the Sun are actually a million years old plus by the time they emerge because they have spent their entire life being bombarded around and absorbed and reabsorbed, ad infinitum almost before they finally escape. So if the Sun went out tomorrow, went out as in all reaction stopped, we’d still have a million years of the light locked inside.

The light is travelling at the speed of light, but it’s only hopping a few centimetres at a time and we don't know what direction it’s going to come back out again. It may end up going back towards the centre of the Sun again and it takes a million years. It’s quite a random walk for that energy to get to the surface.

Are air cavities in the body a problem when diving deep?

Are air cavities in the body a problem when diving deep?

It is a very good film and it does seem very futuristic, but it is actually partly reality. These chemicals, these liquids do exist. They're called perfluorocarbons. They include fluorohexane for example, so a string of 6 to 8 carbon atoms with lots of flourines hanging off the side and they're very good at dissolving oxygen. So, one way of doing this would be to instil these fluids into the respiratory tract and you saturate them with the oxygen, and then you move the fluid in and out, in the same way that you would when you were breathing.

Why this is helpful is that when a person descends underwater, the pressure they feel from the surrounding water goes up and up, the deeper they go. So, you have to therefore put the gas into the lungs to keep the lungs inflated, under progressively higher and higher pressures. One consequence of this is that it drives other gases like nitrogen and things into the tissues at extremely high pressures which means that then when you decompress, those gases come out of solution in the tissues and form bubbles which can cause the bends, they can cause damage to the brain, and cause damage to bones and muscles and so on. So if you use a fluid in the lung, because fluids are incompressible then you wouldn’t have the same problem because the fluid would withstand the pressure being applied by the outside water much better.

The issue with these fluids though is that they're not very good at removing CO2. They're very good at putting oxygen in. They're not good at getting carbon dioxide out and to compensate for the fact that they don't move CO2 very well, you'd have to move a lot of the fluid a lot of the time, and that's one of the major hold ups with doing this. In terms of the liquid getting into other body cavities and body parts, this isn’t such a problem actually. The eustachian tubes that you mentioned, they run between the back of the throat and the ear, so they would just fill up with the fluid anyway. The other body cavities, well, they wouldn’t actually be exposed to the fluid directly because it will be in the respiratory tree. So, there wouldn’t be a problem there and if there were any leakages of the fluid into other places, you would just pass it, I would think. It certainly wouldn’t become part of the systemic circulation, so it should be okay.

If dark skin absorbs more heat, why aren't native African people white, and Inuit people black?

If dark skin absorbs more heat, why aren't native African people white, and Inuit people black?

Logically, it should be the case that if you have pale skin it’s going to reflect more light and more heat and would be suited to warmer, sunnier places. But what is actually happening is people with darker skin have more melanin, more pigment, in their skin and this prevents the short wavelengths of light, the UV, from penetrating deep into the skin. It also means the skin can produce vitamin D in suitable levels. So if you live in more northern climes where there is less sunlight, so for example in the UK, then it’s much better to have pale skin which allows more sunlight to get into your skin and more vitamin D to be produced. Vitamin D is great for strengthening bones. Iit prevents you from getting diseases like rickets which would be very selective against a population if you were living in northern Europe.

UV radiation damages folic acid which you need for the development of the nervous system. If you get folic acid depleted you get diseases like spinabifida, so in continents like Africa where there is a lot of UV in the sunlight, if you don’t protect yourself with lots of melanin you will depete your folic acid, leading to an excess of neural tube defects like spinabifida and this would manifest in a cost to reproductive fitness in the population. So as there is so much sunlight, Africans can afford to have dark skin and still make enough vitamin D and not lose their folate but once you get up to the parts of the latitudes we live in, where it’s miserable all the time, vitamin D becomes the real problem. You need to make enough vitamin D and so you have to have pale skin. There’s so little UV because we hardly ever see the Sun anyway that it doesn’t become a problem from the folic acid depletion, neural tube defect perspective.