Question

Qfwfq · 05-24-2007

Quote:

Originally Posted by InfiniteNow

Planck time is more a representation of the smallest (currently conceivable) possible measure of the passage of time that has any meaning... Like the tiniest possible break between two clicks of an incredibly fast stop-watch...

Not exactly, Planck is a scale below which physics isn't expected to have the same description.

Quote:

Originally Posted by InfiniteNow

Mostly gamma rays, but the smack of energy in a point like locale would probably result in some spacetime ripples and gravity waves... Again, though, I'm just guessing on that.

Rest energy (mass) gets converted into gamma rays but the overall energy doesn't change, it certainly doesn't suddenly increase.

Quote:

Originally Posted by InfiniteNow

...recall my comment above that a matter antimatter collision mostly produces gamma rays. Your question about brightness and color of an annihilation event must take that into consideration, since brightness and color are generally descriptions used on light in the visible range of the electromagnetic spectrum... much less energetic than gamma radiation.

This is the most obvious thing about his question. A (slightly) less obvious thing is that, if it isn't done far from anything else, some of the radiation will volatilize surrounding stuff, rapidly becoming thermal. To get an idea of what it might look like, just watch a film of one of those nuke blasts, one in which the decrease in mass is about 40 grammes (which means a perddy beeg nuke I'd say).

Gardamorg · 05-24-2007

So your saying that if some thing collides fast enough, it will convert surrounding mass into energy?

CraigD · 05-24-2007

Quote:

Originally Posted by Gardamorg

I'm struggling on what a faster collision, about 4 times as fast as a regular collision would do, because they magnetically collide in two ways, not just anti matter and matter colliding, but a magnetic field made of anti matter and a mag field attractor made of matter colliding.

There’s no such thing as a magnetic field made of antimatter.

Depending on the theory you chose for an explanation, a magnetic field is either a description of the force experience by body with a given charge for a range of points in space, or many virtual particles (photons, a kind of boson, responsible for both EM radiation/light and magnetic force).

Particles of antimatter can have net charge. The most common ones, positrons and anti-protons, do. Their charges are the exact opposite of their antiparticles, the electron and proton. The magnetic fields they can produce are no different than ones produced by ordinary particles.

The energy released by collisions at different speeds between equal masses of matter and antimatter is easy to calculate. It is simply $E=mc^2$ , where $m$ is the total mass of the matter and antimatter, $c$ the speed of light in vacuum. Using the mass Gardomorg gave in his initial question, 20 grams of antimatter and 20 grams of matter, the energy produced in a collision at very low speed is about $.04 \mbox{kg} * ( 3 \times 10^8 \mbox{m/s})^2 = 3.6 \times 10^15 \mbox{J}$ , roughly the same amount of energy released by a megaton (1,000,000,000 kg) of TNT, or the amount of energy used 100,000 typical US homes in a year.

If both bodies collided at slightly greater than the speed of sound (350 m/s), per special relativity, their masses would be slightly higher – $\frac1{\sqrt{1-(\frac{350}{3 \times 10^8})^2}}$ , about 1.00000000000068 times, or about 2042 J greater, an increase equal roughly to the amount of mechanical energy required for an average person to climb a 1-story flight of stairs. For a lot of speed (by everyday standards), that’s not much of an increase.

If the bodies collided at a very high speed – say, each moving toward a common collision point at .99 c – their masses would be much greater - $\frac1{\sqrt{1-.99^2}}$ , about 7.1 times, greater.

However, there’s little advantage to artificially accelerating the 2 bodies to such speeds, as the amount of energy required to do so must be at least equal the increase in energy due to their increased mass at the time of their collision. In practice, accelerating bodies to high speeds is usually very inefficient, requiring thousands of times more energy than is given to the bodies, so such a system would use more energy than is released by the annihilation of even the increased mass of matter and antimatter.

Attempts to “trick” nature into giving a lot of energy with the addition of a little appear to be becoming a habit of yours, Gardamorg. It is, I think, likely to be an unproductive one – one of the beauties of physics is that it can be used to find the maximum amount of energy produced by various systems without much knowledge of the details of how it’s produced. I’d suggest you work on some mechanical basics before looking for engineering efficiency tricks. Here’s a fun, not too basic problem. It may require a bit of study to solve – it requires that you know how to do some basic algebra.

Note that, according to classical physics, which applies well to bodies moving only very small fractions of the speed of light, the energy gained by an object of mass M accelerated to a speed v is $E=\frac12 M v^2$ [1]

According to mass-energy equivalence, the energy gained is $( M_{\mbox{after}} - M_{\mbox{before}})c^2$ . [2]

According to special relativity, $M_{\mbox{after}} = \frac{M_{\mbox{before}}}{\sqrt{1 – (\frac{v}{c})^2}}$

Show that, for speeds much less than the speed of light, the energy given by [1] is about the same as given by [2]. For a specific mass and velocity – say 1 kg and 300 m/s – calculate the difference between the energy given by the two equations.