Since the LHC is probably the largest accelerator that will ever be affordable, further advances in beam energy will require new technologies. Are things like using synchonized lasers or plasma waves a viable possibility?
I think so. As background for others: the largest particle accelerators today boost their payload with oscillating electric fields in a resonating “radiofrequency cavity” (RF cavity pic #1, RF cavity pic #2). The RF part of the name just indicates that the field oscillates at, well, radio frequencies. In a circular accelerator like the LHC, the idea is to time the oscillations so that a particle making a complete loop around the ring and returning to a cavity gets there just in time to see:
(a) an electric field pushing it in its direction of travel (acceleration), or
(b) an electric field pushing it against its direction of travel (deceleration), or
(c) no significant electric field (storage).
The energy gain a particle receives in each “cavity crossing” is limited by the maximum electric field strength in the cavity. This, in turn, is limited by the breakdown voltage of the cavity materials. To get to higher energies, you can squeeze a little more out of RF cavity design or you can build bigger accelerators with more cavities around the ring (expensive).
A new technology being developed, called plasma wakefield acceleration, gets its electric fields a different way. You start with a plasma (hot gas of electrons and positive ions) and you disturb the spatial charge distribution of the plasma using a laser or electron pulse. The goal is to make one side heavy on the negative charges, and the other heavy on the positive. A packet of beam electrons passing through during this disturbed moment will feel the electric field set up by the spatial imbalance of charge. And, since this electric field is localized (and away from the walls of the plasma cavity), it can be quite large without running into materials limits.
Prototype wakefield accelerators have had good success. The next step is to apply these in the real world (small-size middle-energy setups). The hope would be that one could subsequently scale the technology up to the energy frontier, but there are quite a few baby steps to take between here and there.
Asides on RF cavities:
The above description of RF cavities leads to a corollary: RF-accelerated beams are not continuous beams; the payload is pulsed. Picture a stored particle making its way around the ring. This particle must encounter no electric fields in the RF cavities, and the oscillations in the cavities are phased up to make this so. Now picture a hypothetical particle in the ring trailing behind the first particle. Say it is far enough back that it reaches each cavity a quarter of an RF cycle later than the first. This particle will see a large electric field and will be accelerated. Again in the next cavity. And again. Soon, it will actually catch up with the first particle. It will then overtake it, but it will also then see opposing fields as it reaches the RF cavities too early. In the end, all stored particles settle stably* inside RF oscillation “buckets”. Thus, the delivered beam comes in pulses, in time with the RF oscillations. (An additional corollary you might notice is that the ring has a fixed number of buckets it holds in its circumference.)
*there are challenges, of course, in getting particle trajectories to dampen down into the desired, stable path.
To achieve a theory that unfies/supercedes General Relativity and Quantum Physics, do you think GR will have to be modified to fit QM more closely, or vice-versa?
Current efforts lean toward describing gravity in analogy with particles physics. I’m not sure I’ve ever heard of anyone attempting the other direction (describing particle physics in a framework analogous with GR). Even in the first case, though, I wouldn’t expect the unification to contain a sort of “modified GR”. My guess is that GR would stay put, and a wholly unrelated description of gravity would be invoked. But, developing unified theories is far from my realm of expertise!
What’s your favorite maverick “wouldn’t this be cool if it were real” alternate theory?
I’m not one for favorites. But, wouldn’t stable wormholes be pretty cool?
Are magnetic monopoles a dead end in current research?
I wouldn’t say that monopole searches (or any exotic searches) are a dead end. Grand unified theories often predict their existence, although usually at much higher energies than we can probe, but those theories don’t have to be right, so I say: if it excites you, keep looking for it. I’m not up on the latest in this small subfield, though.
Is the weak force almost certainly a fundamental force, or could it be just a manifestation of a deeper force?
It could be anything. True, we have no good evidence for any substructure at the moment. But, I think the words “certainly” and “fundamental” rarely make sense together in any sentence.
Quantum entanglement. Layman’s terms, if that is even possible.
Take some quantum characteristic of a particle, say its spin. For an electron, spin can have one of two values, which we’ll label plus and minus.
A central theme of quantum mechanics is that you can have an electron whose spin is not well-defined. Rather, this electron is half in the plus spin state and half in the minus spin state, and up until the point that you measure the spin, either answer is possible. You should not think of this scenario as “the electron has a specific spin, but I don’t know which one until I measure it.” It is experimentally demonstrable that the scenario is actually that “the electron doesn’t have a well-defined spin yet, and both answers are possible for this single electron, and when I measure it, that answer will become the electron’s spin.” (The process of measurement is an active one, so this shouldn’t sound magical. That is, to measure is to interact, so physics can happen during the measurement process.)
Entanglement makes things one step weirder. Instead of preparing a single electron to be in this so-called “superposition” of spin states, you can prepare two electrons. And, if you choose the right preparation process, you can also rely on a conservation law to ensure that the spins of the two electrons must be opposite. That is, if one is plus, the other must be minus. But now you’ve created two electrons that each have undetermined spin but when you determine the spin of one of them, the other (I’ve claimed) must be opposite. Picture the conundrum: you prepare these two electrons and send them far apart from each other, to different rooms even. It can be shown that electron A and electron B indeed both have unspecified spins – both answers are still possible at a fundamental level. However, if two lab techs in these two rooms measure the spins now, they will always get opposite answers, even if there isn’t time for a message to travel from one electron to the other. In other words, the system of electrons had two possible states: A=plus/B=minus or A=minus/B=plus. Measuring just electron A to be, say, plus removes the possibility of measuring B to be plus.
This is similar to the single electron case (where the electron was simultaneously in the plus and minus states), except now our two electrons are simultaneously in multiple states in a correlated way. The electrons are said to be “entangled”.