concrete physical universe (or multiverse). And suppose that the theory of

everything (TOE) is discovered by someone. There exists concrete objects

(elementary particles, fields, superstrings or whatever) that just exist.

They are a priory objects. Also space-time is an a priory quantity. Every

process is explained in terms of these quantities. No questions related to

the fundamentals of the TOE can ever be answered in principle. Of course,

one might say that the TOE isn't the last word and there exists an even more

fundamental TOE2 that explains more than the TOE, however this can't go on

forever, because with a physical universe, you have to have fundamental a

priory quantities.

One of the questions that can never be answered is:

Why does Nature use this particular set of equations?

Out of all mathematical systems there is one that has a special status,

because they constitute the TOE.

Another mystery is consciousness. Physical objects (including the brain) are

made out of the a priory objects. However, since consciousness is the

result of computations performed in the brain, you can replace the brain by

any device that performes the same computation and you are still dealing

with the same person. The a priory objects thus don't generate

consciousness. It is the particular computation that is performed using

those objects that matters. It is thus conceivable that an ants nest could

function like a complex neural network, causing the nest to be conscious.

If you run the TOE on a computer then sooner or later you will see devices

evolve that run other mathematical systems inside them (e.g. people). It

thus seems that I am a mathematical system in itself, different from the

TOE, that happens to be generated by the TOE.

The independence of consciousness on the a priory objects suggest that Bruno

is right. The physical universe doesn't exist. All that exist are abstract

mathematical systems. One of these mathematical systems defines me. I exist

because I can be described. Also, to make predictions about the ``real´´

world, one needs a probability distribution defined over the set of all

mathematical descriptions. Using this probability distribution and a

description of the observer, one can compute the outcome of experiments.

In some old cultures it was believed that the earth was carried by

elephants. The obvious question: what carries these elephants? Would be

answered by: They are carried by other elephants. The idea of a concrete

physical universe faces similar problems.

Brett Hall wrote:

> Because I do not believe that what you think of 'abstract' objects

actually exist. Here we get into what it means to 'exist'. Everything we

have 'access' to comes to us through our sense organs or our imaginations.

This is how we know something exists. What are the exceptions? Apparently

only these 'abstract' objects.> Consider the alternative "It is possible 'abstract' objects exist -

abstract objects we know about -but which are not expressed in any physical

way". This seems to me to be absurd (because to know about an abstract

object one must already have rendered it in the brain somewhere).> I stick with my 'necessary' criterion for now!

If you say that the 'concrete' world doesn't exist, well then I think what

>

> How do you have access to this abstract world if not through the physical?

we are saying to each other is probably actually the same thing - the only

difference is a linguistic one. You just call your world an 'abstract' one -

I call mine the 'physical' one.>