***Be careful! What I said was that "If one defines downhill with a carpenters level ..."! Certainly there exist alternate definitions of downhill which do not make water run downhill by definition (the direction of my front walk to the driveway for example).***
It was perceptive of you to catch Aurino's naive view toward definitions. However, I question whether a carpenter's level defining downhill is a suitable definition, it certainly lacks a scientific quality.
Such a definition is dependent upon the gravitational circumstances that are present depending on the location of where the experiment is performed (i.e., to determine which way the water in the level is tilted). If you do the experiment on earth, then water flows 'down', so your definition of downhill is 'down'. However, if you do this experiment in space where a no-gravity situation exists, then the water does not flow 'down'. If done falling at faster than free fall speeds, then the water would flow 'up'. The definition is completely arbitrary! This is not a good characteristic of a definition in which a degree of universality is sought. For example, you don't want to ask each time someone uses the word 'downhill' the question "where was the experiment performed that determined the direction of your use of the word 'downhill'?" That would be tedious and impractical.
Most scientific definitions generally have a universal quality. Sometimes new unexpected conditions require that further definition be added to the former one (e.g., speed of light in a vacuum versus just the speed of light), but these are factors that take place on-going over the years, not something that are completely subjective such as the above hypothetical definition of 'downhill'.
***No, from my proposed perspective, time is a completely subjective illusion.***
Well, then everything could be considered a complete subjective illusion. The chair I'm sitting on could be a complete subjective illusion. The reason we consider it real is that enough of us experience the same sensations and experiences such that we stop thinking of experiences as subjective (i.e., occurring to 'us' versus having some 'outside us' quality). No one knows what 'outside us' is, so from that point of view every sense sensation is subjective. We draw the line on what the far majority of us experience under careful scrutiny. For example, if we all experience certain sensation as raining, then we say it is definitely raining and it is not a subjective opinion. The passage of time falls into this category. Most of everyone experiences the passage of time, so we consider it a real experience. The question haunting us is whether the passage of time is real from a reductionist perspective. It might reduce to other factors such as a collection of Nows that exist in some quantum Platonia (to use Julian Barbour's definitions). This is what is not known.
***To think that our subjective experience of time is controlled by a clock is to get the whole thing backwards.***
No one says that a clock controls time anymore than a thermometer controls the temperature. Clocks and thermometers merely measure the outside conditions. Clocks measure in an abstract manner the current direction that the earth is pointing in relation to the sun. This is a measurement of time since we define the units of time in terms of the relation of the earth's rotation to the sun. We can take this measuring standard and translate it to 'what if' scenarios (e.g., how old is the universe which predates the earth and the sun). The 'what if' character (or counterfactual) is justified since we can test if the passage of time as it is 'now' is exactly the same in terms of atomic and molecular reactions as they occur in their proportionality. Had atomic and molecular proportions changed, we would certainly see these changes in terms of the radiation spectrum from incoming stars and galaxies. The laws of physics look remarkably the same, hence the conclusion is that the passage of time is identical to our experiences today (e.g., how the earth rotates with respect to the sun).
***The average distance between galaxies increases with time. (If we could be confident that the measured distances are correct.) Now to me that is a pretty big if subject to many questions, but to the academy there is practically no "if" there at all. It is all very well understood if you don't believe me, just ask them.***
Dick, why do you think that this is a big 'if'? Any departure in terms of the speed of light, variation in certain other physical constants, etc can all be safely expected to be seen in the vast amount of data coming from the stars. True, there might be slight variations in the fine structured constant, but there is good reason to suspect that it cannot be significant - at least enough to completely distort our understanding of the universe. A great deal of scrutiny is applied to these issues and a great deal of debate occurs.
Is it possible that God could fool us? Yes. But, all of science is in the same condition of subject to being fooled. Science cannot function on the basis that every well-founded inference is in error. If it did account for every possible error, then science could say nothing of any substance. Certain assumptions (e.g., naturalism) are needed in order for science to offer predictions and experiments to test those predictions. There is nothing that can eliminate these kind of 'potential pitfalls', it is simply the nature of science.
Warm regards, Harv