Why

Mainstream: It accounts for the steady success of science in finding causes, and for the use of 'why' in everyday life.

Alternative: It accounts for why the chain of 'why' seems never to bottom out, and why the origin of the laws resists explanation.

Mainstream: If chains of 'why' kept ending in unexplained dead ends where no further cause or law could ever be found, the answer would fail. Dead ends of this kind exist, such as the origin of the laws themselves, but whether they are permanent is not settled.

Alternative: It would be wrong if a reason for the universe's existence were found. Nobody has found one, but that cannot show that none exists. The view's holders treat the lack of one as confirmation, so little could count against it.

Mainstream: It has no account of what would end the chain for the universe as a whole, so it handles the origin of the laws no better than its rival does.

Alternative: Declaring something a brute fact is a way to stop asking, and it could be said of any unsolved puzzle. Past 'brute' facts, such as the unexplained constants of an earlier era, later received explanations.

Mainstream: It accounts for everyday experience, the thermodynamic arrow of time, and almost all experimental results.

Alternative: It offers a local, realist account of quantum correlations that avoids spooky action at a distance, and it takes the symmetry of the laws seriously.

Mainstream: A reproducible experiment showing a present outcome that depends on a later free choice, beyond what ordinary quantum correlations allow, would count against it. None has been observed.

Alternative: A retrocausal model would be shown wrong if it made predictions that differed from standard quantum mechanics and experiments contradicted them. Current models reproduce standard quantum predictions, so no such test has been made.

Mainstream: It does not explain why physical laws are time-symmetric, or why quantum correlations that break local causality arise. Some theorists think retrocausal models handle these.

Alternative: It reproduces the same predictions as standard theory, so its extra details do no extra work. It also does not show that the future 'pulls' events in the purposive sense the view claims, which goes beyond what the models support.

Mainstream: It accounts for the success of physics without positing anything extra.

Alternative: It offers an intelligible reason for the constants and for the appearance of fine-tuning.

Mainstream: Finding computational artifacts, such as a lattice cutoff or glitches, would count against it. None has been confirmed.

Alternative: Detectable artifacts of computation would support it, and none have been found. Any absence can be explained away by saying the simulators hide them, so little could count against it.

Mainstream: It cannot rule out a simulation, and has no explanation for the fine-tuning of the constants.

Alternative: The goals can be set to fit any observation, and it only moves the question up a level, since the simulators' own world needs a 'why' as well.