It had been a couple weeks since I had seen Taylor (the androgynous being I took for an alien and use ‘shi’ and ‘hir’ for). Having taken a course on Relativity that talked about SpaceTime as if it were a fact, I was interested in hir understanding of this. However I could not predict when shi would appear nor what we would discuss.I was sipping my standard latte and when I put the mug down, there shi was across the table from me. No sound and no introductory ‘Hello’ — as usual. Rather than wait, I immediately started to pose my dilemma to hir: “Relativity theory says space and time are integral parts of our universe. Cosmologists also appear to say that our universe is expanding. How can ‘time’ expand and how would we measure this progressive change, having already accounted for time?” Taylor gave no clue that shi was surprised by my question. “What do you think time is?” shi questioned back to me.“Well, it is the progression of events from the past to the present and into the future.” “And how do you measure time?” Taylor responded. “We use a clock to measure time, using a standard unit as for other measurements.” I responded, hoping the addition of the ‘standard unit’ would look like I knew something. “How do you determine the standard unit?” Shi came back with another question. I started to feel like I was in a Socratic dialogue, each response followed by another question. “I believe it is a measurement of an atom’s periodic event — I don’t know the specifics.”Taylor changed back to statements rather than another question — at least initially: “The specifics are not important for this discussion. You could just as well have chosen a different event or standard for your unit of measure. The point is that you are, in all cases, measuring events — changes in what occurs in space. So you are not measuring some abstract continuum, like your early scientists believed. Nor are you measuring anything abstract at all. You are measuring changes in objects located in space.” I must have looked puzzled as I asked “So I’m not measuring time?” Shi smiled and continued “Correct. Time, as a continuum, is an heuristic method — not a real dimension of the universe.”“Please define ‘heuristic’ for me?” I asked still puzzled. “Think of an accurate model of your house. It is not your house, yet it can help with all sorts of questions about your house — which rooms connect to others, what is in each room, the relative measurements of each room. An heuristic method is a means to understanding something, yet it does not mean it is that which you are trying to understand. Maybe the word ‘model’ works better.” Shi paused and must have seen a glimmer of understanding in my face. “Spacetime is a useful heuristic to understanding aspects of the universe, say general relativity, however there are many reasons why ‘time’ cannot be a dimension like a physical dimension.”Given the course I was taking, I had to respond to this: “Then why do our (sorry — my) scientists think it is an actual dimension of the universe?” Taylor paused before responding “If you built a model of your house the same size as your house, would you think you could tell the difference?” “The model probably only has some things built into it that my house has — so there would be items and aspects of my house that would not be in the model.” I provided. “And in the same way, modeling time as a dimension only captures some of the characteristics of a dimension. You cannot move backward in time nor can you change the rate at which time progresses (even if you experience time as progressing at different speeds). Unlike length, width, and height, there is no way to directly measure time, since any measurement is of a change in objects in space. And try to measure a change in time — like the expanding spacetime universe. In what ‘time’ would time change? It is a useful tool for understanding — an heuristic method.”This seemed unsatisfactory to me. How could nearly all our scientists believe in spacetime and it just be a model? “Then what are all human scientists referring to when they talk about spacetime?” I asked, exasperated. “If you did not know the house model was only a model of someone’s house, might you confuse the model with the actual house?” I considered this line of thought “It depends upon how good the model is.” I replied. “If it is a good model, I might mistake it for a real house. But if it only looks like a house, say no running water, no electricity or anything, then I would be able to tell it was just a model.” “Good response.” Taylor complimented me. “I believe one of the definitions of your word ‘heuristic’ is as a speculative concept — a practical tool that can assist with solving a problem. So maybe your scientists are mistaking the model for reality as they do not have an alternative — they are working with a model that they have not yet understood has a problem.”I considered this for a bit, then had to ask “What sort of clue might help them understand the real problem and that it is an inaccurate model?” Taylor and I had reached this point before “You are asking for an answer to something humans have not yet understood. I can provide a direction to look, but not an answer.” Shi paused then “You call the symbol ‘i’ the square root of minus one — which you unfortunately call an imaginary number. And you use ‘c’ as the speed of light in a vacuum and then ‘t’ for the measure of time. Consider that the original concepts used by Dr. Einstein held the fourth dimension as ‘ict’ and Dr. Minkowski interpreted it as measuring ‘time’ and created the concept of ‘spacetime’. This is an error — as noted previously, time cannot be a dimension except as an heuristic tool. Using just the units of measure for ‘c’ and ‘t’, you can find that ‘ct’ becomes a distance or length. So how might you understand a distance measurement of an ‘imaginary’ (your words) value?” I recalled from high school science class that velocity is distance over time and this multiplied by time would have time units cancel and just leave distance. And then we still had to include the imaginary ‘i’ making it an imaginary distance. I corrected myself — a complex distance (calling it imaginary made the problem seem impossible). When I had completed this thought, Taylor was gone.