There are many ‘big’ questions in metaphysics.
There is also a longstanding debate about whether metaphysics is a waste of time.
Metaphysics is one of the ‘four pillars’ of analytic philosophy (in no particular order):
Epistemology (what is knowledge?)
Metaphysics (what exists and how?)
Ethics (what is right and what should we do?)
Philosophy of mind (what is the mind and how do minds happen?)
The foundation is arguably formal mathematical logic, although probability theory is increasingly included as science advances.
Metaphysics has been called rubbish since at least the early 20th century, when the famous mathematical physicist and logical positivist philosopher Rudolf Carnap declared it a waste of time. Later, empiricist Willard Van Orman Quine was less dismissive. Yet, many leading contemporary philosophers of physics tend to agree with Carnap.
So why bother with metaphysical questions at all? The most common response is that physicists — the new arbiters of reality — often develop metaphysical theories and posits themselves. For instance, David Wheeler is known for participatory cosmology, and John Barrow and Frank Tipler for the anthropic cosmological principle.
The Biggest Metaphysics Question?
The biggest questions in metaphysics tend to be large existential ones about existence:
Why is there something rather than nothing?
What, exactly, is nothing?
What is time, and is it real?
What is causality?
What does it mean for something to be physical?
Is infinity real?
Then there are major secondary questions, such as:
Is strong metaphysical determinism true? (Is everything that happens determined purely by prior physical states of the universe, down to the ‘micro’ level?)
Is physicalism true? (Do only physical things exist?)
Can time go in reverse?
Can causation go in reverse (retrocausation)?
This brings us to what I consider the biggest question. To address it, we must temporarily set aside the question of why there is something rather than nothing. This is because, while there is clearly something, there seems to be no way of answering the "nothing" question without simply concluding that "evidently, a state of absolute nothingness—whatever that is—was not possible." I am not arguing that something cannot come from nothing. However, if it can, its occurrence was evidently inevitable, because here we are.
So, accepting that something exists, the biggest question becomes:
Are there turtles all the way down?
In other words, does the microscopic world extend infinitely downward, ad infinitum? Or is there a smallest possible physical structure? (We will confine this question to the realm of physics.)
To phrase it another way: Is the universe composed of material structures that continue downward ad infinitum?
Or, differently still: Does a smallest, most fundamental scale exist?
In terms of information: is there a limit to the amount of information within any given volume of spacetime, or does the structurally-based information continue forever in both the smaller and larger directions?
The relationship between the "turtles question" and the limits of information is why I consider it the most significant question of all.
The current best answer to this question is the Planck length. This is the smallest possible measurable size that the Standard Model of particle physics allows.
In contrast, the Planck length is about 100 quintillion times smaller than a proton!
At this scale, quantum effects dominate, and our current understanding of physics breaks down.
However, as is common in quantum physics, there is no certainty about what is happening at this level. For all pragmatic and practical purposes in physics, there is nothing smaller than the Planck length.
This means that one of Einstein’s primary metaphysical questions remains unanswered: Is the universe discrete rather than continuous at its most fundamental level? In other words, is nature smooth, possessing a continuous structure at the tiniest scales, or is the entire universe built from what are effectively three-dimensional 'pixels' of Planck size?
The question is significant because if the universe is discrete at its fundamental level, this would limit the amount of structure, and therefore information, that can be contained within any given volume of spacetime.
Since the empirical data required to resolve this question is currently unattainable, it has little practical value for most physics research.
However, the search for the Higgs boson or ‘god’ particle is happening at smaller scales than the size of the proton:
On July 4, 2012, the ATLAS and CMS experiments at the Large Hadron Collider (LHC)—located at CERN in Switzerland—announced the discovery of a new particle with properties consistent with the long-sought Higgs boson. Its mass was approximately 125 GeV (about 130 times the mass of a proton). The Higgs boson is considered a point-like entity with no spatial extent. Its mass, however, is substantial—around 125 billion electron volts (GeV/c²).
Now, physics seems to be discussing 'turtles' smaller than the Planck scale, suggesting the Planck length answer may not be the final word. Moreover, in the first fraction of a second after the Big Bang, all matter was allegedly compressed to a size smaller than the Planck length.
Does the Higgs boson contain information? Yes, of course. Anything that exists contains information; existence itself is a necessary and sufficient condition for it. The Higgs boson’s hypothesized lack of spatial extent is part of its information. Its alleged property of having mass but no structure is also part of that information (though whether having no spatial extent is synonymous with having no structure is another difficult question).
Does the information stop there? If the Higgs boson is real, is there any more data to be gleaned from it?
For other hypotheses, such as whether we are living in a simulation or whether panpsychism is true, this information-centric and structure-centric question is likely crucial.
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