Scientists need to alter the theory of gravity to explain the universe

The argument

Over the past half-century, no one has ever detected a single dark matter particle. Scientists have conducted many experiments with powerful and sensitive instruments, searching in the Antarctic and in abandoned mines. They have also tried to make dark matter particles in accelerators in the lab, which would sidestep the problem of waiting for one to arrive. Scientists came up empty-handed after all these experiments. That record is what gives the alternative its force. A hypothesis that has been searched for by every available method, across decades, in the places most favourable to finding it, and has produced nothing, is a hypothesis whose absence of evidence has begun to accumulate. The right option to consider is therefore not to keep looking for hidden dark matter, but to modify the laws of gravity — to revisit the assumption that generated the missing mass in the first place, since the shortfall was inferred from gravity's behaviour rather than observed directly. Some scientists have proposed that gravity acts differently on a normal scale than on a large scale, such as at the scale of stars. Some want to adjust Newton's second law, which states that applying force to an object will lead to higher acceleration. Adjusting this law may remove the need to invoke dark matter and explain why stars far away from the sun rotate at an equal or higher rate than stars closer to the sun — the very anomaly that dark matter was introduced to account for. Numerous papers have shown that the laws of gravity can be modified to yield exactly the behavior we see in stars and galaxies, which means the observations can be explained without positing an undetectable substance at all.

Premises

Counter-arguments

Changing the laws of gravity is very difficult provided that ample theoretical and experimental data support Einstein's theory of relativity. Scientists' proposition to change Newton's second law of motion is also a huge undertaking because of the vast applications of this law in physics.

Rejecting the premises

[Rejecting P1] Non-detection constrains the possibilities without establishing non-existence. The searches have ruled out particular candidates across particular mass and interaction ranges, which is not the same as ruling out the category, and physics has precedents for particles that went undetected for decades after being proposed. [Rejecting P2] Modified-gravity approaches were constructed to reproduce galactic rotation curves and do that well, but rotation curves are only part of the evidence. Gravitational lensing, the structure of the cosmic microwave background, and the observed separation of mass from visible gas in colliding galaxy clusters all point the same way, and modified gravity has had persistent difficulty at cluster and cosmological scales — with some versions reintroducing unseen mass to cope. [Rejecting C] The conclusion also understates its own cost. General relativity is supported by an enormous body of theoretical and experimental work, and any replacement would have to reproduce it everywhere it has been tested while doing better where it has not.