I have been finding it useful to focus on the present moment: that the past and future are not important to the business of being, and that consciousness is inherently a thing "of the moment". Obviously, your knowledge of the past and your ability to think about the future are both essential and important, but I've found that being present in the now is the best way to be.

Life is made up of thoughts, sensations and emotions, all of which are things that only exist in the present moment. Anything which isn't 'right now' is either a memory or a projection into the future. Your memories are not separable from the structure of your brain, and the act of remembering is actually something that happens in the present moment.

So, let's establish some definitions: 'exists' is defined as "having objective reality or being", as opposed to a 'construct' which is "an ideal object, where the existence of the thing may be said to depend upon a subject's mind", as opposed to a real object, where existence does not seem to depend on the existence of a mind.

According to these definitions neither the past, the present nor the future can be said to 'exist' in any objective sense, nor can they be said to be anything other than a 'construct'.

Physics tells us that the usual conception of time being a universal present that moves through a directional time line is incorrect - that the past and future exist in the same way that two points in space ('here' and 'over there') exist. Indeed, expirimenters have shown that future actions can influence past events through quantum entanglement - which seems to negate the common view that time has a direction leading from the past to the future.

So it looks to me that physics doesn't provide an answer to this question.

I've noticed that whenever I'm feeling unhappy it's usually (always) not the present moment that's the source. It's always thoughts that are rooted in the past or the future. Also, I've noticed that the practice of focusing on a sense of presence in the now has been a really powerful way for me to overcome depression. It now looks to me that having a sense of bliss is in fact the simplest thing in the world, that simply arises from being present in the now.