What is Truth?
Well, that’s a really difficult question.
Let’s begin by asking what we want it to be. For a start - as sentient beings - we want an absolute state of reality which everyone agrees upon. It should be verifiable by means of measurement and documentation. It should provide a stable platform by which we share experiences and communicate. It should provide the foundation for reason.
There are three limitations.
At a fundamental level any sequence of events is constrained by the reference frame in which it has occurred. That is to say that observers sitting in reference frames that move at different velocities to each other record events they see in any other reference frame differently to observers that sit within it. This is because the speed of light is a universal constant (ie if everyone agrees on the speed of light regardless of their relative velocities then they cannot always agree on measurements of space and time) and becomes significant if the differential speeds are massive. The differences may not be relevant in the time and space occupied by a bunch of humans hanging about on a medium-sized planet in what we think is a modest but possibly special solar system of a none too special galaxy - but it should reflect on how we think about an “ultimate” Truth.
The second problem arises when we take things down to the very smallest level - ie to the atomic and subatomic levels. At this level we observe that the entities that populate it (whether they are massless like a photon, or have mass like an electron) behave either as waves or particles but never both at the same time. The problem is that our conceptualisation (not to mention the maths) of how a wave should behave and how a particle should behave are at complete odds with each other. So we end up with weird things (ie nonintuitive because they do not match our regular, everyday observations of the world) like how the act of measurement leads to the “collapse of the wave function” and to “spooky actions at a distance”. Granted not all phenomena can be explained in mechanistic terms - ie by the simple dissection of component parts (like stripping down the parts of an engine) - but if we do not want to factor in some magical, inexplicable, ingredient to explain how things work then we need to be able draw a connection where the basic building blocks of the universe (and their interactions) ultimately leads to the higher level function of everything - from baking a cake to black holes to the human brain. An unbroken chain where particle physics explains chemistry, chemistry explains biology (or baking a cake), and biology explains living systems. We are not there yet, but the search for an “ultimate” Truth suggests that “there” is where we want to go.
The third problem is a processing problem. This one’s harder. The first two problems can be dealt with dispassionately: differences in observations within and without reference frames can be calculated away*, and the resolution of the smudge of probabilistic wave functions can be grappled using concepts like entanglement and superposition, and novel tools like quantum electrodynamics, string theory, and supersymmetry**.
Processing is different. Processing is observer-dependent and introduces the potential for problems at several levels. Problems may arise during the gathering of information (eg from shortcomings of the senses and/or the angle and quality of exposure), the correlation with internal registers (eg the depth of experience, the level of education, the breadth of vocabulary, the limits of imagination, the immutability of certain values and beliefs, the entrapment of personal history), not to mention the influence of environment, prevailing culture, and current emotional state. Throw in some random craziness for good measure and you have your average human processing unit. Such units are very good at producing personal versions of the truth. The problem is that personal truths always seem more real than anything else out there.
Let’s unpack that last sentence. Personal truths are a means by which we relate to the world around us. Once internalised they have salience and leverage and are readily excused from the rigour of validation. That itself is a formidable counterpoint to the curious human disposition for causation, atomisation and universality.
I don’t think we have come to terms with an “ultimate” Truth - or if such a conceptually satisfying possibility even exists. Certainly not to the satisfaction of physicists who might think deeply about such matters. But in my world of online forums and comic books there are many versions of the Truth... often interweaving with a host of non-truths, factoids, made up gap-fillers, repurposed histories, and counterfactuals.
So what is Truth?
Well, it has a lot to do with the question you ask.
Let’s begin by asking what we want it to be.
* Using the Galilean transformation in Newtonian physics if the reference frames are moving at different velocities but not accelerating wrt each other (and factoring the effect of fictitious forces/ d'Alembert forces if they are); or using the Lorenz transformation in Special Relativity which allows space and time to stretch and compress (SR doesn’t burden itself with accelerating systems); or using hugely complex calculations in General Relativity which does away with inertial/ non-inertial reference frames by bending space and time to the effect of gravity (matter).
** Just as relativistic mechanics tells us that space, time, and gravity are not as we think of them in the everyday sense of those terms, quantum mechanics tells us that the entities that populate the subatomic realm cannot be simply defined by wave or particle properties travelling within some “space” in the everyday sense of those terms. There lies a deeper understanding that goes beyond the everyday human experience.