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Comment by mrfusion | Hacker News Reader

The solar system is already close to a vacuum. Makes me wonder if a new solar system sized accelerator could just be a series of nodes orbiting far out to aim and accelerate the particles around.

Still way too hard for us but also way easier than building a tube going around the solar system.

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The tube isn't just to provide a vacuum; it's there to provide continuous acceleration of the particles while keeping the charged particles in the particle beam from dispersing.

There's another issue though.

The reason that accelerators are circular is so that you can keep applying an electric field to accelerate the particles. The catch is, that when you accelerate a charged particle, it emits a bit of radiation, and this radiation increases with the amout of acceleration it's undergoing. The problem is that while you can keep nudging the particles faster and faster tangentially to the track, the circular track requires you to increasingly pull the particles back to the center of the track (i.e. apply a greater centripetal force).

This means that you increasingly lose energy what is called 'synchrotron radiation'. This means that you have a maximum speed (or energy) that you can accelerate particles to with a given radius. Hence if you want more energetic particles in your collisions, you need bigger colliders.

So if you had just a bunch of point to point satellites, you'd lose the benefit of having a greater radius (which doesn't actually apply anymore because you're not doing continuous acceleration anyhow), because you have to increase the amount of acceleration you have to apply at each satellite to pass it to the next one.

http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/synchro...

What if we just built a really long, straight particle accelerator in space, and we just shot all our highly accelerated particles outside of the solar system? Aside from really ruining someone aliens day in a billion years, what’s the disadvantage of doing this?

That's a linear accelerator.

https://en.wikipedia.org/wiki/Linear_particle_accelerator

Presumably, you want to actually see the results of your collision.

The nice thing about rings or other methods like racetracks etc is that the particles come around and go through the same accelerator structure multiple times. Secondly, if you want to collide two beams, the advantage of a ring is that each particle has multiple chances of scattering of the other beam, as it "comes around" to the intersection region millions of times. That being said, linear accelerators are a thing, as they have other advantages.

> The solar system is already close to a vacuum

No. Not at all. You can expect particle density to be anywhere from 5cm^-3 to 80cm^-3 if you stay within 1 astronomical unit distance from the Sun. Besides, all that plasma is accompanied by frozen-in magnetic field, plus you have energetic particle events, recurrent fast solar wind emerging from coronal holes and plethora of other effects and structures which are terribly interesting to study but which will ruin your high energy physics experiment even if you somehow acquire god-like powers and build a huge non-contiguous accelerator.

With a space-based facility, it seems like we'd be able to observe the types of collisions we're talking about without bothering to build an accelerator at all, if we only knew when and where to look for the events.

https://en.wikipedia.org/wiki/Oh-My-God_particle

It's possible that forward progress in the post-LHC era will come from better sensing technology, rather than larger accelerators.

>5cm^-3 to 80cm^-3

had to look this up to see what you mean. I think you mean 5g(cm^-3) to 80g(cm^-3)

Um, water weighs 1g/cm3. He means 5 particles.

No he means 1 particle per that volume, or maybe that many particles per cm^3. The numbers you suggest are more dense than water.

alright, so 5 particles per cm^3 to 80 particles per cm^3, not grams (as density is normally measured).

i'm not sure why the downvotes were necessary though when I made it clear I was trying to figure out what he's saying.

I was under the impression the best artificial vacuums here on earth are nowhere near as empty as space. Is that not the case?

People can get slightly better vacuum pressures in elaborate lab settings than are present on the moon. With trivial amounts of effort (and non-trivial sums of $), you can get within a couple orders of magnitude. Source: have done so myself.

The difference is that space is filled with lots of other stuff that makes running experiments less than ideal.

Charged particles radiate away energy if you accelerate them (force them on a curved path), this energy loss is larger for larger accelerations / smaller radii.

To bend the particle beam you need magnetic fields. Particles with more energy need larger fields. Larger radius means less field strength for given energy or larger energy for given field strength.

So a circular accelerator needs strong magnets nearly everywhere to force the beam on a circular path. In case you would put it in outer space, it's not like you just bounce the beam between some small number of spacecraft, that wouldn't gain much if at all, you would need something very similar to the structure in the LHC.

It would be tricky to anchor them in place so they don't wander out of alignment.

We keep gps sattelites in a very precise orbit. Maybe that can scale up?

Also maybe the nodes could have some kind of magnetic ram scoop design to cover a larger area and funnel the particles through.

> We keep gps sattelites in a very precise orbit. Maybe that can scale up?

Source for this? It was my understanding they weren’t, hence why the almanac data is so important, but I’m not positive that assumption is valid so I’d love a source to back up your claim.

Almanac is important for receivers to optimized what vehicles to track and when. The ground stations comment is the correct answer.

https://gssc.esa.int/navipedia/index.php/GPS_Ground_Segment#...

We aren't redirecting streams of high energy particles with GPS satellites.

>> We keep gps sattelites in a very precise orbit.

I think it's more like GPS orbits are precisely known, not so precisely controlled. If you have fixed ground stations the GPS sats can accurately figure out where they are (like GPS in reverse). If the GPS sats can transmit their location and time accurately, your receiver can figure out your position accurately. The only thing that needs to be well controlled in this is the ground stations locations, which are not moving.

Yup, early in my career I worked in the group, at the JHU/APL, that did the satellite location calculations for the Navy's version of GPS.

One of the research projects to help with this, actually in effect to have carefully controlled orbits, was a "drag free" satellite. Basically just put the satellite in a ball. Then the ball still has drag, but the satellite does not. Sure, soon as the satellite without drag moves with respect to the ball that does, have to tweak the orbit of the ball to keep the drag free satellite at the center of the ball.

There are cosmic rays many times more energetic than anything we could hope to create on earth going through space all the time, we’d just need a detector out there.

There's the ISS-CREAM cosmic ray detector on the space station that can "measure elemental spectra of Z = 1–26 nuclei over the energy range 10^12 to >10^15 eV" Given that CREAM is roughly 2x1x1m^3 and weighs 1258 kg while ATLAS on the LCH is "46 metres long, 25 metres in diameter, and weighs about 7,000 tonnes" it may not be possible to put LHC-class detectors in space

https://cosmicray.umd.edu/iss-cream/ https://en.wikipedia.org/wiki/ATLAS_experiment

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