Would it be possible to convert our assorted cyclotrons, linear accelerators and particle colliders to emit a directable stream of particles?

Hmm, actually converting existing accelerators? That sounds highly impractical.
However there are nuke-powered ion-propulsion drives designed to do just that, toss particles out the back end at extreme speeds, exchanging momentum with the spacecraft (acceleration).

“Propelling light sails” ... but the light sails are a propulsion system themselves. They catch solar wind. If you direct a beam from a spacecraft onto light sails on the same craft I don’t think you’ll have a net gain of momentum.

@dabbler Ah, but you see, this comes from a Star Trek overdose. You would be converting those accelerators in the eleventh hour, when all of your ion drives are out of reach and the normally impractical becomes necessary.

The propulsion idea was from Avatar, where a ground-based laser would push an orbiting sail. The faster-than-light version in-universe was about as unrealistic as the rest of Hollywood Science, but the theory makes sense for slower speeds and shorter ranges.

Particle beams disperse with distance far more than lasers. It comes with the beam being composed of like-charged (positive) particles that repel each other. They’d need A LOT of help to punch through the atmosphere anyway. Stick to lasers or masers.

@hiphiphopflipflapflop why can’t you use neutrally charged particles?

@phaedryx how do you accelerate them, then? ;) In theory, one can add electrons back into the beam downstream to neutralize it or start with negative ions and then strip off the extra electrons after they have been accelerated. A neutral particle beam with laser-like lack of beam dispersion would be an ideal weapon in hard vacuum (atmospheric dispersion would still render it useless elsewhere). Work has gone into this for SDI, naturally, but my impression is they have a long way to go to catch up with lasers.

Basic physics, if you had the accelerator on the ship aimed at it’s own sails, it would not move

I know how to make an interplanitary shotgun but that’s about it. What you’re suggesting is insane. That’s like using the explosive force of a nuke to move a pebble. unless you are moving a planet into a whole new orbit. That particle stream would blow a hole through most materials on Earth if I remember the numbers correctly.

@XOIIO As mentioned above, these would be ground-based, not ship-based.

Oh, so a weapon. Then it would be easier to just just dig a tunnel several miles straight down, fill it a quarter full of water, put a 3–4 megaton nuke at the bottom, stack large titanium plates over the opening and detonate the nuke. It’s like a shotgun on every drug on Earth.

@Nullo you might enjoy a book I’ve recently started to read by Michio Kaku, Physics of the Impossible. In it he talks specifically of concepts from science fiction television and movies and expounds on what it would take “to get there from here”, and how likely some of the concepts are to ever come to fruition. It’s an interesting book (and I see that it’ll be on Discover television starting in December, too.)