TL;DR: Our technology falls short to know the true one-way speed of light. It casts serious questions on our understanding of reality including if two events should be deemed happening simultaneously, even if they are unfolding right in front of your eyes.
No one knows the real speed of light:
One mind-boggling thing I learned a few weeks ago was we have no way to measure, and test the one-way speed of light. All our methods to measure it uses the round-trip time it takes, i.e. the time it takes to return after reflecting from an obstacle at the known distance from source. Ridiculous it might seem but every single trick we have up our sleeves to measure the one-way speed of light turns out to be faulty in some way that actually starts to feel spooky really quickly. And what this means has mind-boggling take-aways. One being the entire concept of simultaneousness becomes subjective and twisted.
The coder inside me turns philosophical:
One parallel I draw from this revelation when I put my coder hat is about creating wrappers around more fundamental blocks of code that abstract away to internal details. So whenever I think deep about it, I feel could feel that our perception of reality is also a wrapper class instantiated object of blueprint of a more fundamental and fine-grained details of reality that runs our universe. Could it be that similar to software development it makes our lives easy but less flexible? Hard to deny unless proven otherwise or it could just be a matter of perspectives.
The bigger picture:
I have always believed there is more to what meets the eye when it comes to the perception of reality. After all, we rely on theories that align with whatever we can measure. Our inability to measure things accurately suggests our mathematical models that explains our measurements are faulty and part of the more fundamental truth which surrounds us but is still obscured to a ridiculous degree. And it applies even to the simplest of our day-to-day experiences such as talking to our partner, and buying groceries. Whatever the fundamental truth really is, when we eventually figure it out, we would look back and wouldn’t be able to fathom how primitive we still are in 2021 to the true repository of knowledge of our universe and reality.
Some resources I used to learn more about it are as follows:
Sanjay Thakur 