"Why is there anything at all?" (or "why is there something rather than nothing?") is a question about the reason for basic existence which has been raised or commented on by a range of philosophers and physicists, including Gottfried Wilhelm Leibniz, Ludwig Wittgenstein, and Martin Heidegger, the last of whom called it "the fundamental question of metaphysics".
The question is usually posed totally and comprehensively, rather than concerning the existence of anything specific, such as the universe or multiverse, the Big Bang, God, mathematical and physical laws, time or consciousness. It can be seen as an open metaphysical question, rather than a search for an exact answer.
On causation
The ancient Greek philosopher Aristotle argued that everything in the universe must have a cause, culminating in an ultimate uncaused cause. (See Four causes)
Bertrand Russell took a "brute fact" position when he said, "I should say that the universe is just there, and that's all."
Philosopher Brian Leftow has argued that the question cannot have a causal explanation (as any cause must itself have a cause) or a contingent explanation (as the factors giving the contingency must pre-exist), and that if there is an answer it must be something that exists necessarily (i.e., something that just exists, rather than is caused).
Apart from these previous arguments that propose that a first cause has always existed without the need of coming into being, some have suggested the possibility of an infinite regress, where, if an entity can't come from nothing and this concept is mutually exclusive from something, there must have always been something that caused the previous effect, with this causal chain (either deterministic or probabilistic) extending infinitely back in time.
Arguments that there may be no need for causation
David Hume argued that a cause may not be necessary in the case of the formation of the universe. Whilst we demand that everything have a cause because of our experience of the necessity of causes, the formation of the universe is outside our experience and may be subject to different rules.
Criticism of the question
Philosopher Stephen Law has said the question may not need answering, as it is attempting to answer a question that is outside a spatio-temporal setting, from within a spatio-temporal setting. He compares the question to asking "what is north of the North Pole?"
Noted philosophical wit Sidney Morgenbesser answered the question with an apothegm: "If there were nothing you'd still be complaining!", or "Even if there was nothing, you still wouldn't be satisfied!"
Mathematical necessity
Philosopher of physics Dean Rickles has argued that numbers and mathematics (or their underlying laws) may necessarily exist.
If we accept that mathematics is an extension of logic, like philosophers such as Bertrand Russell and Alfred North Whitehead did, then mathematical structures like numbers and shapes must be necessarily true propositions in all possible worlds.
Physicist Max Tegmark wrote about the mathematical universe hypothesis, which states that all mathematical structures exist physically, and the physical universe is one of these structures. According to the hypothesis, the universe appears fine-tuned for intelligent life because of the anthropic principle, with most universes being devoid of life.
Physics
Physicists such as Stephen Hawking and Lawrence Krauss have offered explanations (of at least the first particle coming into existence aspect of cosmogony) that rely on quantum mechanics, saying that in a quantum vacuum state, virtual particles and spacetime bubbles will spontaneously come into existence.
Nobel Laureate Frank Wilczek is credited with the aphorism that "nothing is unstable." However, physicist Sean Carroll argues that Wilczek's aphorism accounts merely for the existence of matter, but not the existence of quantum states, space-time, or the universe as a whole. Carroll concludes, as did Bertrand Russell, that "any attempt to account for the existence of something rather than nothing must ultimately bottom out in a set of brute facts; the universe simply is, without ultimate cause or explanation."