this is a particularly powerful topic that you are opening. I have quite a few findings on this matter and would love to hear your thoughts and others’ as well.
In my experience, I can see that mind can know the present moment in a sharper or wider range. For example, as we live in our daily life, we can cognize fairly a lot of objects at the same time, but they are rather superficially known. It is like taking a torch and switching it from a sharper beam to a wide-angle beam. Let me make myself clear - I am describing here my experience. In there I can see the reality in a wider angle but superficial, or I can apply a sharper beam of observation and see the characteristics easier. It is possible for me to be mindful in both ways - wide-angle and sharp-angle.
Another point I have is regarding these “past moments”. As soon as you start talking about past moments, you run into troubles with MN Bhaddekaratta and other such suttas. Some teachers based on these “past moments” assumption suggest that it is not possible to observe present moment.
However, I totally disagree. The Buddha explained we should observe walking when we are walking, sitting when we are sitting, standing when we are standing, lying down when we are lying down. Breathing in when we are breathing in, breathing out when we are breathing out. We observe greed when we have greed (santaṃ vā) and when we do not have it (asantaṃ vā). The Buddha never suggests that we observe a past moment, so that idea seems to me as frivolously non-Theravadin, non-Buddhist, and totally unacceptable.
Now, how would I explain that we observe the present moment? Through the speed of mind. If it is so, that mind arises-passes billions of times per snap of fingers, then there is no need to talk about past moments. The multitude of moments of mind within a short period of time allows us to perceive present moment by present mind, albeith this would be just a vague perception.
Think of a ceiling fan, that has only four blades. These four blades turn round and round very fast and make up a perception of a disk. However, there are blades and air. The observing mind vs. the observed mind would be like the blades vs. the air. They do not happen at the same time but we feel and experience it as if they happened at the same time. They alternate very fast.
This idea of alternating makes it possible for five aggregates to happen at the “same time” or at least to be perceived so, and it allows for mindfulness to be happening at the present moment in accordance with Bhaddekaratta and other suttas.
Let me know your thoughts on this and if there is any Sutta/Commentary/Subcommentary/Non-Canonical scripture that I may like to read. Or if you have any additional questions/concerns regarding my experience.
May you be happy and healthy.