First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)

[ignoramus]

Alex. Throw a bit of light on "other" dimensions.
Could/Do these other dimensions take up the same space/time as our dimension/reality?
How would they work if they were to exist? Different frequency? What does that even mean in today's theoretical physics?

[Foxaèr]

Oh, gosh.....I wonder sometimes.

[Alex K]

The colloquial concept of "other dimensions" or "parallel dimensions" is a bit different from the concept of dimensions as it is used in physics.

In everyday use, "other dimensions" are often a shorthand for a parallel world which can be entered from ours somehow, but is otherwise separate. In physics, dimensions are simply the available directions of space (and time). For example, the space we experience every day has 3 dimensions, and if it has additional dimensions, there must be a reason why we don't perceive them as additional available directions of movement. Models which involve additional space dimensions usually have them rolled up and very small (at least a factor 1000 smaller than a proton) in order to hide the fact that we could in principle move in additional directions. This idea goes back all the way to 1922 and 1926, when Theodor Kaluza and Oskar Klein tried to merge Einstein's gravity theory and Electromagnetism in a five-dimensional scenario, something Einstein tried his hand at as well. Another possibility which was introduced as a crucial element into String Theory by Joe Polchinski in '95 or so, and which was popularized by Nima Arkani-Hamed, Savas Dimopoulos and Gia Dvali was that we might be stuck on a three-dimensional space (a brane or an intersection of branes), and simply cannot move into the additional perpendicular directions.
Lisa Randall and Raman Sundrum in '99 popularized a somewhat different version of that, where we're basically stuck on a 3-dimensional space because of gravity.

In such models, one could have other three-dimensional branes which are literally parallel to ours, but removed from ours in one of the additional perpendicular directions. The stuff on those parallel branes will still interact with us via gravity. As an extreme simplified version of that, one could imagine something like a "parallel world" which shares our three-dimensional space with us but is otherwise separate. That's very simple to construct mathematically, you simply duplicate the Standard Model, but don't let one set of particles interact with the other. If the two worlds share one space, they will still interact via gravity, and our matter would be attracted by planets and stars in the parallel world, but not collide with them, which is an intriguing idea, but probably not realized in nature like that, because parallel galaxies would have shown up as gravitational lenses. But if the "parallel" particles don't clump to solid matter, that's basically what the worst case for dark matter could be (because we can't study those particles in colliders or detectors if they don't interact with our particles.

One might of course simply postulate that the parallel world has separate particles and separate space. That's in the way the simplest possibility, but doesn't seem to make any predictions and hence is not very interesting scientifically unless one specifies some kind of interaction between those worlds.

Alex. Throw a bit of light on "other" dimensions.
Could/Do these other dimensions take up the same space/time as our dimension/reality?
How would they work if they were to exist? Different frequency? What does that even mean in today's theoretical physics?

[I_am_not_mafia]

Btw. the huge machine you see in the picture is used to hold just a minuscule amount of Antiatoms at once. The setup from Dan Brown's Angels&Demons is completely impossible with current technology, because it is super-difficult to trap just a few electrically neutral atoms without them touching the walls, let along grams of them.

There's a similar problem with fusion isn't there, creating a reactor that will last long enough. Could it be that doing all these experiments in zero gravity is the key to further progress? Of course the cost of getting out of the Earth's gravity well is too expensive. I can't help thinking that automated asteroid mining is critical to humankind's future.

[Alex K]

Btw. the huge machine you see in the picture is used to hold just a minuscule amount of Antiatoms at once. The setup from Dan Brown's Angels&Demons is completely impossible with current technology, because it is super-difficult to trap just a few electrically neutral atoms without them touching the walls, let along grams of them.

There's a similar problem with fusion isn't there, creating a reactor that will last long enough. Could it be that doing all these experiments in zero gravity is the key to further progress? Of course the cost of getting out of the Earth's gravity well is too expensive. I can't help thinking that automated asteroid mining is critical to humankind's future.

I don't think gravity is the big factor here. Remember that in a gas at room temperature, the individual molecules making up the gas bounce around at almost 2000 km/h. You either need to cool them to ridiculously low temperatures to have them sit still-ish, or confine them somehow.

[Alex K]

p.s. Even if they'd cool down to CMB temperature of 2.7K, they would still move out of your machine in a matter of milliseconds without confinement...