Gravity Already Pushes: How Antigravity Could Be Real. The Routes That Physics Still Allows, How Strong Each One Can Get, and the Experiments That Would Decide Them

Antigravity is usually treated as fantasy, but general relativity does not forbid gravity from pushing. Gravity is sourced by energy density plus three times pressure, so any medium with strong enough negative pressure repels. The universe contains such a medium: the dark energy that has been accelerating cosmic expansion since its discovery in 1998. The real question is therefore not whether repulsive gravity exists, but whether it can be produced, concentrated and controlled on a human scale. This paper maps every route that current physics leaves open: vacuum (dark) energy, negative Casimir energy, gravitomagnetism, negative mass and antimatter, warp-type geometries, and new short-range or spin-dependent forces. For each I give the physical principle, the experimental status and a calculated magnitude. Three routes are real effects already observed (cosmic repulsion, negative Casimir energy and frame dragging), but at laboratory scale they fall 16 to 36 orders of magnitude short of cancelling Earth’s gravity. To cancel g under one’s feet, a floor would need a negative active mass of 2.3 × 10¹⁰ kg per square metre, as much as a column of rock 8,700 km deep with its sign reversed: 2 × 10³⁶ times the density of cosmic dark energy in a one-metre slab, or a stack of ideal 10 nm Casimir cavities fifteen million light years thick. A spinning disc would need about one-seventh of nuclear density. Two routes are closed or unsupported: antimatter falls down, and no device claim has survived replication. Energy conservation adds a design rule rather than a prohibition: hovering costs nothing, but switching gravity off costs at least mgh. I conclude that antigravity is physically possible in principle and already real in nature, but not achievable with any known material. The most likely way it becomes real in a laboratory is through a small, precisely measured effect, and I identify the experiments, chief among them weighing vacuum energy, that could show it.