proposed future colliders (FCC, ILC, muon collider)
/ eff-see-see; eye-ell-see; MYOO-on /
The LHC will not run forever, and well before it stops physicists must decide what, if anything, to build next — a decision that takes decades and billions of dollars. Several large proposals are on the table, and each makes a different bet about how best to push past today's frontier. None has yet been approved for construction; they are studies, designs, and arguments about the future of the field.
Three ideas lead the discussion. The FCC (Future Circular Collider) is a proposed CERN ring around 90 kilometres in circumference — first as a precision electron-positron machine, later possibly as a very-high-energy proton collider — essentially a bigger, bolder LHC. The ILC (International Linear Collider) is a proposed long straight electron-positron linac; being straight, it dodges the synchrotron-radiation wall that limits circular electron machines, and it would deliver clean, precise collisions for detailed study of the Higgs. The muon collider is the most adventurous: it would collide muons, which are like heavy electrons. Because a muon is far heavier than an electron it radiates far less when bent, so in principle it offers the clean collisions of an electron machine at the high energy of a proton machine — but muons decay in microseconds, making them fiendishly hard to collect, cool, and accelerate before they vanish.
These proposals matter because they frame a genuine strategic choice for physics. Should the next machine chase the highest possible energy to hunt directly for new particles (the energy frontier), or chase extreme precision to spot tiny deviations from the Standard Model (the precision frontier)? Each option costs a fortune and takes a generation, so the debate is as much about scientific priorities and resources as about magnets and beams. It is worth being honest that all of these remain proposals, with real technical and financial hurdles still to clear.
A muon collider could in principle reach proton-machine energies with electron-like cleanliness, but a muon's average lifetime is only about two millionths of a second, so the beam must be assembled and accelerated almost before it has time to decay.
Each proposal bets differently on energy, precision, and buildability.
All of these are proposals, not approved projects; each faces serious technical and cost hurdles, and there is no guarantee any particular one will be built, so claims about 'the next collider' should be read as scenarios rather than settled plans.