was + will = is

The positions of philosophy of time may be divided in three main waves:

1) Presentists believe that only present is real. Past exists only in present memories and future in present predictions (this is the intuitive feeling, but it is not valid under the theory of relativity).

2) Eternalists believe that all three points in time to exist together (past, present and future. Relativity would be eternalist).

3) Growing block theoreticians believe that only past and present are real.

These sum up the discussions about the ontological status of time (or space-time) in physics. I will not try to add to it here. My concern will be the anthropocentric (maybe extensible to most animals) experience of time. The claim will be that 'present' does not exist (in experience).

The nonexistence of present as a human experience is a perplexing idea because under the commonsensical presentist view present is all there is. Watch out Carpe Dienists!

Let us sum up the facts about our perception to reach the result. In an experiment Eagleman& Sejnowski asked people to press a button to light a light bulb. When the interval between these actions was 80 miliseconds people said the light turned on immediately. When this interval was reduced to 40 miliseconds they said the light turned on before they had pressed the button. This happened because there is an 80 miliseconds delay between what we see and when the brain realizes that we have saw. Therefore, when we 'realize what we see' we are seeing 80 miliseconds in the past. Our 'present' experience is of the past. Past presents itself to our subjective experience.

Although, specially in a more natural context of human survival in the wild habitats this difference in milliseconds may be the difference between life and death. To survive one must anticipate predators. If the eyes perceive (limbic system in the brain) the present but the brain takes milliseconds to figure it out (occiptal lobe), brain would be a disadvantage and we would not have evolved to spend so much energy in using it. The caveat lies in the future. The brain may takes some milliseconds but it is not trying to 'perceive' the present (or past as we saw) but to 'anticipate' the future. Kwon,Tadin & Knill invite us to think about when someone throws a ball and we easily pick it. If we acted in the present it would have been too late to pick it. You have to anticipate its trajectory and move your arms where the ball will be a few milliseconds in advance.

If the crossing of information above makes sense we interpret the future out of the past to act as if we were in the present. The casual steps are due to past and future: I saw X at the position p1 moving in time t1 X will be at p2 at t2. Thus past and future are the building blocks of our present experience and the present for us exists only as a supervenient result. Our experience of the present is just another useful illusion which uses past data and future prediction to compose a 'simultaneous experience' of the world.

In sum

We see 80 milliseconds in the past (Eagleman & Seinowski)
We project it in the future (Kwon, Tadin and Knill)
[For it to be worth we have to procees it accurately 80 + (at least) 1 in the future]
Therefore we use the past to project the future (this is what we call 'present')
[The present is properly present only in the cases where the situation is static for at least 80 + 1 milliseconds in the future, so that what we saw in the past and what we project into the future remain the same.]

The next time someone advices you to enjoy the momentum you can answer that one cannot truly experience the present. You might at most commit yourself to use the past data in a useful way to predict a pleasant future. Carpe crastinun the saying should go.