Q n A - 2 :- learning Physics during train travel!

I am happy when people recognize me as a Scientist, in particularly as a Physicist. In the train journey from Bangalore to Mumbai last night, I found many interesting youth in my compartment, asking lots of interesting physics questions. Here is roughly how the dialogue went on for almost two hours! Thanks to Alpa, Girish, Akhilesh, Keyur and Jitender for being such curious students!! And I like being grilled by questions, so thanks for grilling me!! :)

Q: What is the expected outcome of Large Hadron Collider? Can we create another planet from this experiment?
Ans:- Hardly! in LHC experiment,They are colliding two protons at a very high energy. Now, what do you think of a proton as? A kind of solid spherelike a cricket ball, but a tiny and very low mass one, right? In reality, even the proton is made up of smaller fundamental particles, called "Quarks".Now these quarks don't generally leave the spherical boundary of the sizeof the proton. However, when two protons collide on each other with so much energy, these quarks can break up into various combinations, and new particlescan get formed.
Q: So how does LHC experiement give rise to a new Big Bang?
Ans: It doesn't create a new big bang!! Its like this: When Big Bang Happened,Huge amount of Energy was packed in small region of space. And the laws ofPhysics as we know are not valid for such high energy densities. So we cannotstudy the physical situations very very close to Big Bang time. (We can, however,Go upto the microseconds after the bigbang!)So when two protons in LHC collidewith each other, what they do is they pack in a lot of energy in a very smallvolume, thus making a laboratory controlled situation similar in few aspects, to the big bang.
Q: So is it really worth spending all the money, on this biggest experimentof science? Cant we not use it for some social cause?
Ans:- I don't think that social causes are not being taken care, and lack onlymoney. Scientific advances have far reaching consequences not known beforehand.E.g. The GPS system which you use, would collapse in few minutes if the Einstein'sGeneral Theory of Relativity is not used in their calculations. Now GTR givesvery minute corrections, and most of the times we can use Newton's theory of gravitation. However, when your hand receiver gives out signal to 4 satellites,and they correlate their positions and send you back your location details, if they don't apply proper corrections for their positions, then your locationwon't be accurate at all! So who knows, results of LHC experiment may bring outsomething not forseen right now.
Q:So what is your research topic?
Ans:- I am studying the properties of interstellar dust, that between us and the stars. This dust obscures the starlight, and scatters and absorbs it, thusnot giving the correct picture. Its just like a cloud covering the sun. So if I know the size, constituents, spatial distribution of these dust particles,then I can account for their effects.
Q:- How is this dust?
Ans:- Its micron size. Anything more than a hundred atoms bound together is termed as dust. Q:- I thought space was all vaccum, how come so much dust, and how significant is the obscurration?
Ans:- YES, it is a very high quality vaccum out there. Its better than the bestthat can be achieved in laboratories... Still, inside the galaxy, there is lot of hydrogen gas, and also these dust particles.And there is hardly one particleper cm^3, but the distances are so Huge, that it adds up to a large quantity.
Q:- What is this dust made up of?
Ans:- Its largely silicates, oxides, carbon and ice.Q:-If we see a spectra of dust, what do we exactly see, the dust, or the sourceof the light?Ans:- The scattered light will be of the same frequency as the source. The dust absorbs some light, and gets heated up, and emits in Infrared, just likeeven now all our bodies are radiating in Infrared. Now some of the absorbed lightwill excite the atoms in the dust to a higher level, and when it de-excites, it will emit the spectra charecteristic to the dust constituents.
Q:I just don't understand all this, Big Bang and stuff like that. What was therebefore that?
Ans:- Yeah. This is a limitation of linear logic. You will always ask, what was before whatever you know, and what is after whatever you know! Another scheme of logic is spherical logic. Its like this, on a sphere, what is the starting point of the sphere? Any point could be a starting point. This is a gift of Indian Philosophy to the Scientific thinking. There is also a theoryfor beginning of universe, that there was not just one big bang, but millionsand millions of big bangs. Right now there could be something like a Big Banghappening in a distant part of the world!Alpa:- Right now there could be other copies of us sitting in some other part of the world! Me:- Yes very much possible!
See this article.
Q:What is dark matter? how come it became known recently?
Ans:- Its non-barionic matter, matter which doesn't give out electromagneticradiation. Protons are barionic matter. Recently, Astrnomers studied the velocityof hydrogen in different parts of the galaxy, and plotted it from the center of galaxy radially outwards. The velocity curve flattened after a radius, and thiswas not acceptable, gravitationally, if you assume that only the luminous matter is present.So they had to suggest a large amount of unseen matter, which theytermed as dark matter. In absence of any such matter, the curve would have gonedown, instead of remaining flat.
Q: What if I emit light from a car travelling at the speed of light!? Will I see it in front of my car?Ans:- First let's consider a simple situation. Lets say I am standing here, and you are travelling in a car at speed V1. And you throw a ball at speed V2 in same direction. Then I would notice the speed of that ball as V1+v2, right? Now consider the case of light. If you are travelling at speed v, and throw light, which will travel at the speed c, then I will also see the light travelling at speed c!! This is a kind of miracle! This is an experimentally verified fact,and This is subject of relativity, where our notions of time and space are totally changed! E.g. If Akhilesh travels from here to a distant galaxy and comes back, he would find himself younger than his cousin, whom he left at the same age!! This is because, not just clocks, the heartbeats, the wheels, the time itself slows down for a moving observer, w.r.t. a stationary observer!!Girish:- There is a nice description of this in Concepts of modern physics byArthur Beiser.Me:- Yes, and Relativity is not difficult! With pen and paper I can describe to you in few minutes!
See this nice illustration.