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Lasers Approach Their Ultimate Intensity Limit
Flash Modin writes "Death Star style superlasers? Don't bet on it. High-power lasers currently in development appear to be nearing the theoretical laser intensity limit, according to new research set to be published in the journal Physical Review Letters. Ultra-high-energy laser fields can actually convert their light into matter as shown in the late '90s at the Stanford Linear Accelerator (SLAC). This process creates an 'avalanche-like electromagnetic cascade' (also known as sparking the vacuum) capable of destroying a laser field. Physicists thought it might be a problem for lasers eventually, but this work indicates the technology is much closer to its limit than researchers believed. A preprint is available here."
Or even running out of lighter fluid.
If you could track every atom of the lighter fluid, you'd see that there are as many atoms from the lighter fluid around after the combustion as before. In a nuclear explosion, there are fewer atoms around.
Also, they're not talking about a single laser, they're talking about colliding two laser beams.
They're aiming an electron beam at a laser - not quite the same thing as aiming two lasers at each other. Furthermore, the key part is not the e-beam, but the gamma-rays that come from the electron-photon collision, which then interact with the laser. The issue is that once you create one electron-positron pair from photons, you can get a cascade reaction where there are so many electrons/positrons floating around that you don't have a coherent laser field anymore.
It'll be a fascinating sight to see, surely.
Those who can, do. Those who can't, sue.
Well gee, if only there were a link to an article about it.
In a report published this month by the journal Physical Review Letters, 20 physicists from four research institutions disclosed that they had created two tiny specks of matter -- an electron and its antimatter counterpart, a positron -- by colliding two ultrapowerful beams of radiation.
As for this being new...
The possibility of doing something like this was suggested in 1934 by two American physicists, Dr. Gregory Breit and Dr. John A. Wheeler.
Energy converts to matter, and matter to energy, all the time. Check out Feynman diagrams for many examples. Particle colliders are machines built for the purpose of converting energy into matter. When particles collide, some of their energy converts to various forms of matter.
What a fool believes, he sees, no wise man has the power to reason away.
But it is energy that was stored in a either a chemical bond, or an electron state. Matter does not disappear, it is just electrons rearranging their orbits. If you count all the protons, neutrons and electrons before and after the chemical reaction, they're all still there.
Those who can, do. Those who can't, sue.
Both nuclear and chemical reactions destroy matter, if you can call that destroying matter.
In a chemical reaction, electrons change states. In an exothermal chemical reaction, the energy of those electron states is lower than the energy of the electron states before the reaction, and energy is released in another form (photons, kinetic energy, etc.). If you count the neutrons, protons, and electrons, they're all still there. But mass has been lost, because the binding energy of the electrons counts in the mass of the molecule. (In the reaction, binding energy was lost and converted to another form. Energy is mass.) However, chemical binding energy is tiny compared to the energy in the rest mass of protons, neutrons, and electrons.
In a nuclear reaction (fission and fusion), the states of nucleons (neutrons and protons) also change. Again, if you count the neutrons, protons, and electrons, the same ones present before are present after. (Sometimes they change form, like n p + e.) But mass has been lost, because the binding energy between the nucleons counts in the mass of the atom. (In the reaction, binding energy was lost and converted to another form. Energy is mass.) Nuclear binding energy is still small compared to energy in rest mass, but it's a lot bigger than chemical binding energy.
This is a common misconception. No, the particles that result from collisions were not already there. The top quark was created from a collisions of particles that did not contain a top quark. The same is true of bottom quarks, strange quarks, and charm quarks. The particles come from the energy of the colliding particles. That's why the energy of the collisions determines the maximum amount of mass of the particles the collider can create.
Just think about it for a few seconds. If new particles could not result, how can we make new types of quarks and antimatter? When we collide electrons and positrons, how could other types of particles possibly result?
What a fool believes, he sees, no wise man has the power to reason away.
Chemical energy is energy and is matter too. If you measure 8 tons of oxygen and 2 tons of hydrogen (hopefully I got my stochiometry right), and let them react, and cool off, and measure the total weright afterward you will find it changed.
Mass energy equiavelence, scroll to "Binding energy and the "mass defect".
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Well, let's see. Suppose we decide to accelerate an asteroid 100km in diameter using whatever long-term propulsion we can (nuke-powered VASIMIR, big solar sails, whatever) and use the well-known gravity assist that the planets can provide. If the asteroid has an average density of 4 g/cc, how fast would we have to get it going when it impacted earth to give enough energy to blow the planet apart?
Blow the planet apart = move all of its mass to escape velocity. Earth escape velocity is about 11.2 km/sec. 1kg moving at 11.2 km/sec has about 6.27e7 Joules of kinetic energy. Earth's mass is about 5.97e24 kg. (No, I didn't weigh it, but Google is my friend). So, to move all of the earth's mass away at a speed of 11.2 Km/sec would require (6.27e7 J/kg)*(5.97e24kg) = 3.75e32 Joules.
OK, this doesn't count the energy needed to break the rock up, but cut me some slack, this exercise is tuned to the accuracy standards of physicists, i.e., we're happy if we get it within a few orders of magnitude.
Back to our 100Km diameter billiard ball. It's mass is about 2.09e18kg. So, to get about 10^32 Joules of kinetic energy on target, it will have to be moving at about 10,000,000 m/sec. This is about 3% the speed of light.
This is surely overkill in that it's the energy needed to push all the earth's mass to escape velocity. Probably less than 1% of this energy would suffice to crack the planet into pieces. Would this count as blowing the earth up?