QED Ask a Scientist – Francisco Diego
During this year’s QED Conference in Manchester the Cosmic Genome team gave attendees the chance to tweet in, ask us at The CG desk, or even ask on camera, a question to a select few scientists from the Cosmic Genome App.
Dr Francisco Diego
Question - Hi, my name’s Tom [@Askwho on Twitter] and my question is: which, as a percentage, is more empty, an atom or the universe?
Francisco - This question is fascinating, I mean, I’ve been playing with it for a while, and let’s start with space. I mean, assuming that space is empty, which it’s not, but let’s assume it’s empty and it’s populated by stars. So, stars like the sun have a particular size, several million kilometres in diameter, and they are separated by typically a few…in the vicinity of the galaxy, in the vicinity of the solar system, typically separated a few light years away. So, you take the distance between the sun and Alpha Centaurus, which is a few light years away, if we take that distance in terms of the solar diameter, so there will be about…20 million solar diameters all the way to Alpha Centaurus. So this will be the solid, say, the star ,and this will be the empty space, so the factor is 26 million, say.
That will be typical for the space in the Milky Way where we are…that’s a kind of density of stars that we may…so, 20 million diameter of stars separated. If we go to the atom, then the atom is quite a challenge because the atom is not such a solid thing, even the particles that make the atom are not exactly solid, but let’s assume an atom is made out of a nucleus and an envelope, and the nucleus is where the protons and neutrons, its tiny, tiny, tiny, tiny and then it’s empty space, let’s call it empty space to the clouds of electrons around it that define the size of an atom. Now that cloud of electrons is about 10,000 or 50,000 more or less times bigger than the nucleus of the atom. 50,000, OK…
So, the sizes are comparable, not so much of the sizes between the stars and the distances between the stars. So I would say from that point of view that the space is far emptier than an atom. However, if we take the nucleus of an atom and we look inside the nucleus of an atom we find all the particles inside the protons and neutrons, the quarks, the gluons, and we‘re into a place where space is not so much separated from matter and the mass of this particle is not measured in grams, it’s measured in units of energy. So if we go inside that we have a factor of 1000 or 10, 000 even smaller and still it’s not enough to make for the space between the stars, and these are the stars that we were talking about that are in the vicinity of the local area of the Milky Way where we are. If we move outside of the galaxy, between galaxies, there are no stars there, so the density goes down and down, I would say by an enormous factor of space, assuming that space is empty as well, because we’re making a lot of assumptions here, space and stars are far less dense than an atom.
Question [from Mel] - Apart from being a spectacular sight, what can we actually learn from a total solar eclipse?
Francisco - A total solar eclipse is a magnificent thing to see, its one of the…perhaps one of the most spectacular things to see in nature. From the science point of view, it has been extremely important; we have to remember that more than a century ago it was in the sun that the element helium was discovered - and this is why it is called helium - by doing spectroscopy of the atmosphere of the sun at those times. But beyond that the solar atmosphere, I mean, what we see of the sun, the bright surface of the sun for which we need a filter to protect us, to make it dimmer because it’s so bright, that is what we call the surface of the sun which is still gas but it behaves like a solid surface, but on top of that there are at least two layers of gas which is very thin and very faint but hotter and hotter. We are talking about the chromosphere, which is a very thin layer of pinkish coloured gas which is mainly halogen and helium, and then beyond that we have the solar corona which extends towards the inner part of the solar system, in fact, we are immersed in the solar corona from where we are here. The chromosphere is hotter than the photosphere and the corona is even hotter than the chromosphere. The corona is at least one or two million degrees hot and this is something which is counterintuitive, because as you go away from the sun you would expect that the temperatures go down, they don’t, they go up, and this is a major mystery. There are other magnetic fields, particle acceleration because of very strong magnetic fields in the sun, but it’s still…we don’t have a proper answer for that and solar eclipses are a way for us to study those areas of the solar atmosphere that are not this one, not even from space, we have still the possibility of using sophisticated equipment that we can do, even for a few minutes, viewing the total face of an eclipse so they are still very useful, still we learn a lot about the solar atmosphere and the interaction between ourselves, and scientific expeditions are still mounted to see solar eclipses all over the world, indeed from the last couple of centuries.
Question - If we had an unlimited budget, where should we go next in space?
Francisco - For space exploration, we actually have unlimited budget, we can do it straight away, but political reasons and all reasons are not allowing us to do that, we should have been back to the moon several decades ago and we should be on Mars by now, so we have a limited budget. Now, what is the best way to explore space from where we are? We have been to the moon, we have the international space station, what is the next step? NASA wants to go to Mars and an asteroid straight away: I think its a major step to do now. From my point of view, the way to do this is to go to the moon first, establish a base on the moon where we can learn how to live away from the earth, still within reach of the earth, within a few days travel, and learn how to work in low gravity in an environment which is very hostile, with no radiation protection, we have to live underground and we have to be completely autonomous in our habitats there. After a reasonable period of time, we can learn how to do that and we can start thinking about going to Mars. I would take it in these two steps before going to Mars, which is a journey of the best part of a year we have to spend going to Mars and that still is a big problem , it’s a major problem, I don't think we still have the capability to face those challenges; I would go to the moon first.