What we regard as TIME is just a way of measuring duration for various phenomena. Like a ruler is a measuring device for measuring length ( or breadth or width). Saying Time is an illusion is like saying the measuring 'ability' of a ruler is an illusion. Is a measure of length, width, or breadth just an illusion? Why do some scientists or philosophers say Time is an illusion?

• See this article on the block universe. Note that most us regard this as philosophy not physics. – John Rennie Aug 9 '14 at 5:37
• Is a 'measured duration' that is comparable to 'standard' measurement 'tools' (and that can be communicated successfully to many other people) an illusion? – user128932 Oct 20 '14 at 6:01
• The interval between two timelike separated points certainly isn't an illusion. The illusion is the human perception that time flows. – John Rennie Oct 20 '14 at 6:03
• Do you mean the 'illusion' is that time is 'continuous' in its 'flowing'? So Time being 'made-up' infinitesimally small 'bits' of time or 'moments' is an illusion and the 'flow' is not continuous. Just like a line of light bulbs on a billboard lighting up in succession in the 'line' , it looks like ( from a distance) a continuous movement of one light along the line. The 'one' light moving 'continuously' is an illusion but the duration involved is not. Is this an accurate assessment? – user128932 Oct 20 '14 at 6:14
• No, there's no suggestion that time isn't continuous. The illusion is that it flows. We wouldn't say that distance flows; it just is. The same argument applies to time. Do some Googling for block universe for more on this idea. – John Rennie Oct 20 '14 at 6:52

Philosophically, both time and distance are illusions. Distance is actually more disturbing than time. So first, let's define what "time" is. It is the number of transitions of an atomic state (see atomic clock wiki). Distance, a meter, is defined to be the length a photon (light) travels in $\frac{1}{299,792,458}$ of a second (source) which simultaneously defines both distance and the speed of light!

I think time is confusing because it's not well understood (for sure by the masses and perhaps even by physicists philosophically). The problem is is that if every process happened without time, then every process would happen instantaneously and there would be no existence! As it stands, processes happen as one would expect. First one thing happens, then the next, then the next, then the next, ad nauseam. This progression or chain of events, is what time actually is. If there were no "time" (so to speak) then the chain of events would happen instantaneously and no one could observe anything in the intermediate. But even that language is problematic. Because maybe it does happen instantaneously, but still the progression itself we interpret as "time".

The bottom line is that time is the number of transitions that the universe undergoes from one state to the next. This is an insanely complicated ballet that organisms with our understanding have come to interpret as time. Time is real--it is the transition from one state to another--but the perception of time as is true of all perceptions is an illusion.

p.s. And it should be noted that the term "instantaneous" pertains to time...so I am trying to describe time with our preconceived notion of what time is--which is inherently flawed (i.e. you cannot define something by using its own definition).

• Why is perception an illusion? I perceive your interesting response in my 'mind'. Is your response an illusion? What do you and many philosophers mean by an 'illusion'. Also can 'real' events have a necessary duration in how 'they' occur regardless of whether their happening is measured with 'units of time' or not? – user128932 Aug 10 '14 at 9:37
• What is perception? Perception is your brain creating a world from its input. If we rely solely on perception, then relativity is completely ridiculous--yet it is so. Quantum Mechanics is even more ridiculous--yet it is so. Even further, you ask: "Is your response an illusion?" Yes, because human language while we perceive it to be precise, is not. Therefore, you perceive, from my response, what you want and not necessarily what I was attempting to communicate. ...and all of this belongs more to philosophy than physics (as has been stated). – Jared Aug 14 '14 at 6:39
• how can a 'process' happen instantaneously? – user128932 Oct 22 '14 at 1:58
• IF any perception is an illusion how can any measurement of such illusory information be taken as real or verifiable as the processes involved in any measurements can not be separated from perception. – user128932 Oct 23 '14 at 19:19