Presentism is true. Meaning, only the present is real and non-abstract.

First off, science is interesting and wonderful at giving descriptions of our experience of the world.

Science is still ultimately empirical (experience-based) even when we're dealing with the most theoretical of the sciences. Everything ultimately has to go through the human lens. And even if there is some super-advanced alien civilization out there that has a science far more advanced than our own ... that, too, would have to be filtered through experience---it's just that this time it would be filtered through their experience rather than ours.

All the wonderful science we have ultimate relies on our conscious experience. 'Conscious experience' treated as a tautology that basically just means 'experienced experience'. I am talking about the most basic consciousness .... just the ability to experience reality in some way. To be aware. Not needing to be self aware or have cognition of any sort (and even cognition is ultimately just another type of experience).

So, why have I gone on this, perhaps, apparent tangent? It's to start off with an explanation to point out that if I deal with any of the usual "general relativity disproves presentism" or "presentism is unscientific" arguments then this is to point out how they're not relevant. Science deals with our experience of reality rather than how reality is in itself. I will give a couple of examples of this. 

First of all ... what we now call an 'atom' doesn't actually refer to a completely indivisible thing even though that's what the word 'atom' originally meant. This is because science cares more about evidence-based progress and moving to newer and more accurately updated models as quickly and elegantly as possible ... science is not so interested in giving the correct labels to such models. Rather than waste time on using a new word to describe the 'atom' once the atom is discovered to no longer refer to what it's supposed to refer to (atoms turned out to not be the smallest thing once smaller particles were discovered but science kept on calling them atoms anyway) then science just changes the meaning of atom to what it now seems to be. 

Sometimes this is fine but the point is that science is dealing with what it is discovering experientially and evidentially regardless of whether it contradicts current word usage. Science is happy to change the meaning of things to fit its model because it really is just a model. It's the best model we have but it's still a model.

There are examples, however, when it's not so fine. And that's when scientists cause a great deal of misunderstanding by explaining their very valid discoveries very badly. The discoveries are very valid still (almost always) but they can sill be poorly explained. An example of this is the title of Lawrence Kraus's book 'A Universe From Nothing'. A great big misnomer of a title. The book itself contains some brilliant science but the title alone has rightly caused some criticism by philosophers *and* by some more philosophically minded scientists. The reason being because the 'nothing' that Krauss talks of most definitely isn't nothing. Yet again, it's a case of scientists redefining a concept into something they have already discovered. In this case, it's the quantum realm of so-called 'empty space'. I say so-called precisely because this supposed empty space of 'nothing' contains a great deal of quantum activity. Quantum activity isn't nothing. And it may be 'empty' in a scientific sense but it isn't truly empty in another sense because it contains something ... namely, a lot of quantum activity. If it contains anything at all then there is most definitely a sense, or way, in which it isn't truly empty. 

Lawrence Krauss, rather than just admit that he gave the book a catchy title and that "A Universe From Almost Nothing" wouldn't sell as well, doubled down on his silliness, insisting it "really is nothing" and made a great fool of himself. It's a pity really. Philosophers of science could help him if he let them.

So, science redefines concepts if it has to in order to fit its models because the scientific method is all about empirical progress and it's less interested in making sense of concepts in a logical or philosophical way. This is fine most of the time but not so fine when people end up explaining things poorly. It's one thing to do science and it's another thing to explain something well. 

So, with this in mind .... general relativity and quantum mechanics are almost certainly true but they must be true in a sense that is non-contradictory and trusting the evidence even when it contradicts logic is just plain silly at best. 

So, my claim, then, is that the present is the only real, concrete, non-abstract and non-imaginary thing that exists NOW. How shall I argue for this?

I'll simply argue by using what those words actually mean in order to show that it's true by definition. What exists now is what is present now or current now. Now is now. Present is present. Present is now. Current is present. This is all tautologically true by definition. The claim, again, is that the present is all that concretely exists NOW. Well, the present can't exist in the future or in the past because then it wouldn't be the present it would be the future or past. Given the understanding of the claim I spelled out in the description it doesn't seem possible to defeat my argument. It's almost as if by accepting the debate challenge my opponent must have already misunderstood the claim. Obviously, everybody gets the chance but my claim is that the present is all that exists now. Well, that's literally what the present means---what exists now---so it can't be untrue. It can't be false. You can't get any more solid grounds for a claim than a claim based on a pure tautology. My opponent could suggest that my thesis or view was trivial but it doesn't matter if it's trivial because if it's trivially true it's still true. I am arguing for the truth of my claim. I am not arguing for its significance or importance. I am just arguing for the truth of my claim. And it seems that given the way the words are defined and the claim I spelled out ... my claim cannot be false.

I argue that it is silly to say that the past or the future exist now because the past is what used to exist but not anymore and the future is what doesn't exist yet. The present is literally defined as what exists now. 

But I can understand that we do have abstractions of the past and future now. in our minds. This is how we can make sense of the whole concept and visualize and imagine such things as the 'past' and 'future' in the first place. The past and future can exist now AS CONCEPTS. As ABSTRACTIONS. In an imaginary or unreal way. But what was my initial claim? That only the present exists in a non-imaginary, non-abstract, real and concrete way. So the claim covers that already too.

So now I'll lay out a few arguments explicitly:

(P1) Science is ultimately based on empiricism (Namely, our evidence and our experience).

(P2) If science is ultimately based on empiricism then theories of time that say that other things exist now besides the present must be dealing with experiential models of reality rather than how reality is in itself.

(C1) Theories of time that say that other things exist now besides the present must be dealing with experiential models of reality rather than how reality is in itself.

(P3) Since theories of time deal with models of reality rather than how reality is in itself this must mean that those models are dealing with abstract reality rather than non-abstract or concrete reality.

(C2) If science is dealing with abstract reality rather than non-abstract or concrete reality then I'm correct when I say that science doesn't contradict my claim that the present moment is all that exists non-abstractly and concretely.

(C3) If my claim in C2 is not contradicted by science then science can't be used as an argument against my claim.

Okay, so that's the first argument. The point of that argument was to show that science isn't relevant to my claim. That if my claim is to be defeated then it must be defeated by logic alone. Now I shall offer my two arguments for why logic alone gets to my position. It's, thankfully, very tautologically true.

(P1) The present is what exists now.
(P2) The present is not what doesn't exist now.

(P3) P1 and P2 are clearly tautologically true and their truth is merely the statement that the present is all that exists now. This alone gets to the truth of the claim that the present is all that exists now.

(C1) If P3 is true then my claim that the present is all that exists now is clearly true.

(P1) It is true that there is a sense in which 'the past' and 'the future' exist now.
(P2) It is very clear that it is not the future itself or the past itself that exists now as that would be contradictory.

(P3) If the past and future themselves can't exist now but from some angles it seems so then it must be that they seem to exist now rather than they actually exist now.

(P4) If the past and the future don't actually exist now then they must virtually or abstractly exist now.

(P5) My claim is that the past and the future don't exist now non-abstractly.

(C1) Even if the past or future exist abstractly, as concepts, this does not contradict my claim that the past and the future don't exist non-abstractly.

So there you have it. An informal introduction to my arguments and explanations followed by a more formal, but still not too formal, follow-up. I hope it wasn't too boring and that it was readable and well-explained and thought out from the point of view of whoever is reading. And I hope that nobody felt the need to skip sections of what I said as there could definitely be meaning lost if that was done.

Best wishes to everybody and good luck to my opponent.

Science is not merely abstract or theoretical, we can see it very obviously. Look at the sun. It is here now, at the "present", correct? 

OR IS IT.

Light takes 8 minutes to travel from the sun to the earth, my opponent cannot deny this. Thus, during the "present", "now," the "past sun" still exists. We are observing the past because it takes too long to travel to us. As such, the past can exist in the present. It is entirely plausible that the sun has gone out during the "present", but merely that we have failed to observe the change, due to the distance. As such the "present" we observe and the "present" that exists contradict each other. This is a very concrete explanation that contradicts my opponent's case.

If my opponent is not convinced, how can he explain cause and effect? If two things are directly related to each other, then they must both exist. This is an essential truth. As such if it flooded yesterday, its impacts and the wetness of the ground could still be observable today. Even if the only thing that exists in the present is the wetness, how can con disprove that there was a flood previously? It doesn't make sense that it never existed.

my opponent is being confusing. He says the sun existing is the present, but I have already proved it was the past. Science can apply because time and space are just human realized notions. Consider that our reaction times are different, our emotions manipulate how quickly we perceive things, boring things are slow and fun things go by faster, so to two people observing the "present" occurring, one of them may already be in the future while the other is stuck in the past. Consider the double slit experiment, which goes to prove that perception can even change light's travel pattern. As a result, the "present" is muddled, is the present only existing when we are observing, or is it always here? If so, then the present is not the present when humans are not here. If this idealogy can be disproved merely by our nonexistence, then it is not a truth at all is it? A rock is a rock, a tree is a tree, regardless if we exist to observe it. But if humans need to be there to observe the present to be the present, then insane people do not think the present is the present at all. Their minds would warp their understanding, and challenge the idea of the present being the only thing that is present, unlike the potential futures shown by the double slit experiment.