I get your point, but I don't understand what is indented to be "meaning". I guess you mean, super natural purpose, or reason for living. To say their is no intellectual reason to get up I don't agree with. I get up because if I don't I would be laying there all day. Why do you eat? You eat because if you don't you die. Is eating meaningless? I think it means something, it means that our body will digest the food and give us fuel and keep us healthy. That means something to me. It is not subjective that if you don't breath you die.But again, I think you are missing the point. I am not saying that life does not have a subjective meaning, what I am saying is simply that there is -as far as we know- no objective reason for why one should get out of bed in the morning, or do anything at all for that matter.
"The meaning of life" has the same problem as any other philosophical question (or any problem in science for that matter); we basically have to postulate some axioms (which in this case could be e.g. "things that make me feel good makes life worth living") before we can proceed; you can't create a reasonably consistent system otherwise.
But the problem with this is of course that one has to accept these axioms in the first place and you can't persuade someone to do that just by appealing to their intellect.
Now, to a large extent these "axioms" (or whatever you want to call them) are hardwired into our us (we e.g. WANT things, food, love etc and we have reward centres in our brain that makes us feel good when we get them), but the interesting thing with the human brain is that we are aware that these things are just "hardware" meaning we can choose to ignore them or for some reason consider them to be "not enough" (as is to some extent the case in clinical depressions where the "feel good mechanism" do not work properly because of problems with seratonin levels etc).
If you are religious you can also postulate that some of the things we experience as "good" are not merely biochemistry but has some objective value.
No, but it does mean that I can't be SURE that I exist; which bring us back to what I wrote above about the problem with purely intellectual arguments in this case.
It would e.g. be very difficult (I would assume impossible) to persuade a computer (to be more precise a Turing machine) that life is worth living. I suspect that if we some day manage to create a true AI "life is worth living" is one of the things that will need to be postulated in its basic algorithms (and yes, I do realize that this is just Asimov's third law)
You also say that if their was a heaven then there would be a reason, or reward, but what would that reward be other than continued self awareness and "rewards of the mind". Therefore, if life itself has no meaning, then no supernatural existence would have any meaning either.
The very fact that a quantum vacuum can organize into particles, atoms, and so forth until life and self awareness is enough of a mysterious and amazing wonder that I don't need a religion to satisfy my desire for something supernatural. If there is a supernatural meaning to life, then all the better, but other wise, so what. I'm not sure I would want to live forever anyways.