Re: "What IS time" Hi sciforum, My considered opinion, Let's be clear and logical here. Whether it is In fact valid or not,"What IS time" is a leading question. It implies "time" is something that is proven to exist (as more than just a useful idea), and that therefore "it" "is" something. Many people seem to rush off so quickly to try and describe this "thing" that they seem to skip the most basic scientific steps of actually checking what we actually observe, and need to explain. If this initial, unchecked assumption "there is a thing called time", happens to be incorrect, and this is not noticed from the outset, then all subsequent attempts to answer the false assumption will be vague, conflicting, self referential, speculation or conjecture,(this can be confirmed or not for oneself, by cross checking countless other posts on this topic). If the assumption is correct, and time "is" something that has been proven to exist, then we should find out who has the proof and ask them "what is time?". But, because the question is being asked openly and randomly, this indicates that the question may be based on an assumption whose foundation is just assumed. Therefore, I suggest a better, less leading question might be 'What do we actually observe?' to this i would say we seem to observe 1- That matter exists, and, 2- that matter is moving and interacting. From there, I think a sensible question to ask what I call "the key question of time", I.e... "If matter JUST exists, moves, changes and interacts... Would this be enough to *mislead* us into "wrongly assuming", that there is a 'past', 'future' and thing called 'time' "? if this is the case, logically, we are left with precisely what we actually see.. a universe full of constantly changing matter giving us the misunderstanding there may be a thing called time. so, imo - (having written a very detailed book on the subject) - 'A Brief History of TIMELESSNESS' 'time' IS a useful "idea", and system of understanding and comparing examples of motion, (similar to "money" being a useful idea and system), but ,IMO, (unless a scientific experiment as per the scientific method can be proposed to show the actual existence of a "past" and or "future", as opposed to just using those terms in theories "as if" they are a given), not something that actually IS a genuine phenomena. Special Relativity does suggest, and it is confirmed, that any moving oscillator will be oscillating more slowly than expected, but this observation does not prove in any way that there is also an existing phenomena called "time", that exists, and is dilated, where objects are moving. Likewise General Relativity shows that gravity warps space, and dilates rates of change, but again this does not prove there is also a past, future, or a thing called time that exists or "passes". Logically, and scientifically, unless anyone can experimentally show otherwise, it thus seems that matter just exists and is moving and changing and interacting, in all spatial directions. But, not heading in to a "future", not leaving a "past record of all events" behind it, and without a thing called time needing to exist and pass. And therefore the answer to the question... "What is time?" 'May' be , "Time, IS a useful idea and system for understanding and comparing examples of motion, but probably NOT also something that exists. Although most people seem to assume otherwise because they assume without any proof that there 'is' a 'past' and possibly a 'future', and assume without actually checking, that Einstein's Special Relativity, proves the existence of 'time', as opposed to just showing how relatively moving things are changing more slowly than expected". Anyone interested in understanding the "theory of time" in more detail, please take a look at one of my powerpoint talks... Matt Marsden (auth 'A Brief History of Timelessness') Timelessness.co.uk A couple of Videos describing how relativity may still hold it's essence even if it happens to be only about warped space, length contraction, mass increase, and "rate" dilation, but not a thing called time. YouTube: Timeless answers to Brian Cox's Science of Dr WHO. " Time travel cant happen without 'the PAST' " (complete with LEGO intro Please Register or Log in to view the hidden image!