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 Posted: Fri May 22, 2009 7:53 pm
ISIS on the BBCJust this morning on the bus going to work I first read about ISIS. Now from someone that followed the progress of the LHC quite closely, to find out we had a remarkably similar -though not the same by far- project going on much closer to home was quite a shock to me. Not just that, but when I got home and did a little reading about this newfound interest of mine I was shocked on what I found. In the past I have been quite addicted to the GTR. Focusing on the 'Twin Paradox' and thinking up my own scenarios I had gone into quite some detail looking at what technology we currently possess. From this I estimated how fast one could go in space given our current understanding, and from that began calculating how much time dilation would occur. So with the space shuttle's orbiting speed of 13km/sec as a rough average speed for space craft I began work. Back to the ISIS programme. This is where I was shocked. Quite similar to the LHC, the ISIS uses high intensity radio frequency fields to accelerate the beam, as opposed to the super conducting magnets (Or so I gather, bare with me I only heard about this this morning) and in the first acceleration is taken to 25% of the speed of light. Then through the second acceleration -after the proton undergoes a rather confusing process to remove the electrons- it is then accelerated to 84% of the speed of light. So as you can see, when true time travel relies on being able to travel as close as possible to the speed of light, this struck me as hugely interesting. Not only is the LHC accelerating particles to audaciously close to C speeds, but there are much smaller projects that do almost the same thing. My question is this. How much of a gap is there to bridge between accelerating H ion, or some other particle to say... 90% of C, and doing to same to an actual visible, 'real' item? A grain of sugar perhaps, or a small sphere of metal. Of course the energy taken to achieve those speeds would be ridiculous, but something that's less but still quite fast in comparison? What do you think the future holds for gaining speeds close to C?
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Posted: Fri May 22, 2009 9:55 pm
Consider the mass of a hydrogen ion, i.e. a proton: 1.67*10^-27 kg. Since energy scales linearly with mass, it would take 10^27 times the amount of energy to accelerate 1.67 kg to the same speed. A human weighs about 70 kg, so it would take about another two orders of magnitude to get a human up to that speed. So we're talking a difference of 29 orders of magnitude.
Consider the following calculations:
Suppose we want to get the object to 90% of the speed of light and that we can somehow transfer kinetic energy with perfect efficiency into an object. We get that the kinetic energy of a proton at 90% light speed is:
KE_proton = m_proton*(gamma-1)*c^2 = 1.9*10^-10 Joules
For a kilogram, we get
KE_kilogram = 1*(gamma-1)*c^2 = 1.2*10^17 Joules
Thus for every kilogram, we'd need to expend 1.2*10^17 Joules. To give you an idea of how much this is, this is equivalent to burning about 1.2*10^10 kilograms, or about 4*10^9 gallons, of chemical fuel. So it would take about 10^8 barrels of oil, or about the entire oil consumption of the US for a week, to accelerate a kilogram of mass to 90% of light speed.
Assuming a 70 kg person, we get
KE_person = m_person*(gamma-1)*c^2 = 8.4*10^18 Joules
This is about the oil consumption of the entire US for a year and a half.
Note: the energy-to-oil conversions are crude, order-of-magnitude estimates, but they are within an order of magnitude.
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Posted: Sat May 23, 2009 10:57 am
F = MA ... simple physics.
Since acceleration is inversely proportional to mass, it will take an incredible amount of force to get an object moving at the speed of light in a vacuum. If you want to calculate what force it would take to get a small object moving at C, you can simply plug in the mass of the object and the acceleration it would take to get it to C in a reasonable amount of time, and thence the force it would take to accelerate that object.
But considering it takes so much force to accelerate such a small particle to C, I'd guess we don't yet have the technology to accelerate a clump of millions or even thousands of particles. We'd need a million times or a thousand times the force.
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Posted: Sat May 23, 2009 11:28 am
But Layra your example still goes off the hypothesis of having a perfectly efficient kinetic energy transfer right? So it'd be a whole lot more considering the other effects there'd be on the item being accelerated.
So in all realistic (Though hugely sci-fi) ideals, we'd need a much more efficient power source before we could acheive something similar, am I right? As the common fuel just seems far too inneficient we would need some far superior source of energy. I remember reading about the neuclear reactor engine or something that was being designed a while back but I never got through to fully looking into it. Would that then have a better fuel/ acceleration ratio?
I worked out a while back that traveling at 15,000 mph over 10 years would, relative to the passenger, be 8 years and some 2-3 months. It could be wrong, infact it almost certainly is as I did it at work on a scrap of paper from boredom with no calculator. But what realistic speed can you see man reaching either now or within the next 10 or so years? And would anti gravity help in acceleration? I read somewhat into I think it was... donut shaped anti gravity field generators? I'm not 100% on it but i think there was the application of ridiculously fast space travel. I know this is a subject you are familiar with so shed some light wouldja?
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Posted: Sat May 23, 2009 11:43 am
Look, I don't want to make any false presumptions, but I thought E = mc^2 only came in when you were converting mass to energy or vice versa. I'm only thinking about the force it would take to get an object to accelerate that much.
(Then again, I think I remember Einstein's equation being used in accelerating objects to near-light speed.)
(Also, I think force would be the most basic step and then energy the next.)
If these two coinciding thoughts of mine were true, I would be wrong to say the equation isn't related to the subject.
Nevertheless, I believe we should first concentrate on step 1.: whether it's possible to apply that much force to an object.
...But if it were concentrated on energy, once we had figured out the force needed, we would need to concentrate on power. (I don't think we could ever have the kind of power to do that, even if we had the energy.)
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Posted: Sat May 23, 2009 12:25 pm
Well I think the question wouldn't be weather it's possible to apply that much forcr, but how we would apply that much force.
NASA just recently (Few months back) released information about their new probe which is in a 'Kite' or 'Sail' design. It is basically a light weight probe with a huge sail attatched to it made of light weight reflective foil. The idea being that the light from the sun hits the sail, slowly propelling it forwards. So with a constant accelerating force acting on the probe it could reach amazing speeds, depending on how close to the sun it was when it started.
Now that is a purely efficient, free, and reliable source of energy that would eventually take the probe to enormous speeds. I'm not saying close to C speeds, but still fast.
Not just that bit with the idea of the vortex anti gravity field thing, i think the idea is to bend space around the craft in such a way that it meets no resistance from external forces. I could be vastly wrong there but it's been a while. This again would grant us the ability for massive speeds.
So I believe it's certainly possible, or will be within the next decade or two, to apply the correct amount of force to an object to make it travel ridiculously fast, it is just how we will do that that is the main problem.
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Posted: Sat May 23, 2009 6:28 pm
F=ma is the low-energy limit that doesn't take into account relativity. In terms of energy, the correct equation is given by
E^2 = (pc)^2+(mc^2)^2
where p is the momentum and E is the total (kinetic + rest) energy. When the object isn't moving, i.e. when the momentum is 0, then we get that E_rest = mc^2.
Given that equation and a bit of wrangling with the velocity formulas, we get that an object of mass m moving at velocity v has
E = mc^2/sqrt(1-v^2/c^2)
So the kinetic energy KE = E_total - E_rest = mc^2*(1/sqrt(1-v^2/c^2)-1)
Force isn't really an issue, because we can just apply a low acceleration over a long period of time. The total energy needed is too much at the moment.
Nuclear power might be feasible for small masses, although current nuclear capacity is only about 400GW, so it would still take about a year of current nuclear capability to get the kilogram to .9c. We'd need a much better energy source before we can get to highly relativistic speeds.
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