You live entirely in your own imagination.

You know that now doesn't exist, right?

Every particle in the universe can only interact with other particles necessarily separated in both time and space. Particles interact via forces, with their own mediator particles (the electromagnetic mediator is the photon). These mediator particles are constrained by the speed of light. They have a source of emission, and of absorption, separated by a duration and distance. These particles have no independent existence- they are not "real" except as abstractions. Although you can see things that are lit, what's really going on is that a lepton or a hadron is performing a quantum leap somewhere and causing a corresponding quantum leap in your eyeball. From your perspective, something is jiggling your eyeball from another coordinate in space-time. It is also equally true, though, that having your eyeball jiggled necessitates the jiggling of something else in the past; the event itself does not occur 'now' in any meaningful sense, but can be thought of as having discrete energy, length, and period, relative to other space-time coordinates.

The relativity of these space-time coordinates is the important facet I'm trying to get across here, because neither the distance, duration or energy are fixed, or indeed are objectively measurable- they remain constant only in aggregate. Some alien looking at his home star a billion years ago a billion light years away will note a certain distance to the star, the duration of the event, and the energy of the quantum leap, but these values won't be the same from our perspective, because the distant particles are receding from us at a notable fraction of the speed of light, and length contraction, time dilation, and redshift apply (as described by special relativity). Physics treats all such space-time coordinates invariantly, although you can't work out the future end of an event from its hypothetical past one, you can only stab at its probability (using the equations of quantum mechanics).

Events trigger other events, (causality) so all measurable events have occured in the past. That they occurred at all can only be inferred from other events that they cause- for example, seeing a photon of light will trigger a chemical reaction in your nervous system picks upon (or 'is' might be a better term) that makes you know that you saw it.

Setting aside the light-cone aspect of things, which make it pretty clear that there is no 'now' at least in a strictly physical sense, it is an indisputable fact of biology that it takes time for nervous impulses to travel from sensory apparatus to the central nervous system and be processed by the brain. This is why the highway code makes reference to reaction time in the section on stopping distances- it is physically impossible to react to things as they are happening.

What the brain does is take raw impulses that occurred in the past, process them, and project that information forward to create an *imaginary* "now". It does this quite well- this is what allows you to, for example, catch a ball that is thrown at you. We normally think that it takes time for us to react to things that we perceive "now" but it's more than that- the perception of "now" is a projection into the future of essentially out of date information to begin with. This effect is difficult to perceive, because it is not only intimately tied with the essence of what consciousness is, but it is also very well compensated for by the brain's synchronising processes. It is easy to dismiss the importance of it when response time is measurable in fractions of a second, but consider a hypothetical space whale with a brain hundreds of kilometers long. It would think in just the same way as us, be able to dodge asteroids just like we would in our hypothetical space ship, but it would be projecting from old data, say, three minutes ahead; its "now" would be- not old- but three minutes *uncertain*. You could wave your hands in front of its eyeball and three minutes later it would blink- just as if a fly gets in your eye, and you blink it away fractions of a second later. This is because it's "now" is three minutes uncertain. However, if you floated in front of it and three a ball at it that took six minutes to go near it, in three minutes time it would catch the ball. From its perspective, it would be catching the ball "now", having no understanding of any other frame of reference.

It is easy, and tempting, to think of now existing, but that we aren't absolutely aware of it. The problem comes when you consider other reference frames. Think about any given event- for example, clenching your left fist briefly. There is a time before you plan to do it, a time when you are planning to do it, a time when you do it, and a time when you are thinking about having done it. The event itself does not pass from being in the future, to a "present" and onto being in the past; the event occupies a discrete space-time coordinate. At each stage, there is a "you" occupying a different space-time coordinate (and a part of your body, but not the whole "you" occupying the same space-time coordinate). Our perception of these different times is only a recognition of the distance between the "self" at these instances and the event. These states of recognition remain the same independent of the time at which we, in turn, recognise them; in other words, what exists is a recognition of the separation in time between discrete events, relatively speaking, with no fixed zero-point which we can address as "now".

The realisation that now does not exist can only come from the exploration of the related concepts; it is necessarily exempt from the realm of qualia. When you do delve into these concepts, you come to realise the sensation of being is a self-deception, albeit a useful one that has evolved to optimise the prioritisation of information for maximum utility in decision making and in carrying out action.

The rabbit hole goes further, of course. Although the main point I wanted to get across is that "the present" is a non-concept, your grasp on reality is a lot looser than that. Keeping with the theme of visual qualia, consider such a thing as colour. Of course we know that human beings can perceive three wavelengths of light, red, green and blue, and from the sensitivity to these wavelengths we perceive things in a whole range of colours. Consider a red ball, sitting on the table. It is tempting to think of such a thing as a red ball existing- but in truth, it is only red because we are capable of perceiving redness. The ball absorbs and reflects other wavelength of electromagnetic radiation also- x-rays, radio waves, ultraviolet radiation. Although we can certainly say that the ball reflects more red light than green or blue, the ball itself is not red; we have no idea how much of other wavelengths it reflects, and since colour is the result of a mix of wavelengths, the actual colour of the ball is unknown to us. The only thing we can say is that our conception of the ball is that is it a red ball. The concept has no physical analogue- it is only useful for ourselves, and to communicate with other people capable of seeing similar colours (and this does not include all human beings). The ball is imaginary, and we cannot perceive its reality.

Also, and this ties in with what I said earlier about the brain filling in blanks- we only perceive colour across a very small area of the retina. The cones are clustered tightly in an area of the eye directly behind the pupil, with few cones the further out from this point. Yet, we see colours in our peripheral vision. We perceive these colours around us when staring straight ahead not because we are in any sense seeing them- the mind remembers where it saw these colours before, and then imprints upon your spacial awareness the colour that is recalled. It's one thing to 'believe it when you see it'- but most of your field of vision is drawn from your imagination, guesswork based upon your frail and unreliable memory.