# Time, Spacetime, and the Arrow of Entropy

1. Feb 19, 2016

### sanman

Physicists refer to "spacetime", lumping together the dimensions of X, Y, Z, and T as if they're all common and same. This reductionism is the product of mathematical rigor. But in our daily lives, we don't experience T in the same way we experience X, Y, and Z.

I can arbitrarily set the orientation of X, Y, and Z. If I move my hand from left-to-right, I can set that as an X axis. If I move my hand up and down, I can set that as a Y axis. If I move my hand back and forth, I can set that as my Z axis. But I can't choose which way to orient my T axis - it has already been chosen for me - it's already pre-set as an ordinal axis. Nor can I move my hand back and forth in the T-axis, and I am stuck moving through it at some predetermined rate.

So what is this thing called Time and why is it different? What is the reason for this overall discrepancy in how we as human beings experience T differently from X, Y, Z which are otherwise supposed to all be common to spacetime?

After having thought about it, it seems to me that this so-called T axis is really just a parameter for Entropy. I don't want to sound metaphysical, but we human beings as observers experience the world through our brains and what we called "consciousness" - without this we can't observe, and so this is the underpinning of our entire perspective.

The brain and "consciousness" are the result of a electrochemical reactions, whose particular sequence is characterized by increase in Entropy. This series of electrochemical states is the basis for how we experience the passage of Time and the Universe it parameterizes. The sequence orientation necessary for our "consciousness" to occur is therefore what has set the orientation of the T-axis, which can also be construed as the Arrow of Entropy.

So how then does this limitation of how our brains work then impact upon our ability to resolve all the great outstanding problems of physics?

Mathematical rigor seems to be our "yellow brick road", such that as long as we stay on it, then we are supposed to be able to navigate our way through even when we're otherwise without any other bearings. And yet, being able to re-map the mathematical picture back onto the real world context is also necessary for meaningful interpretation and problem-solving.

Does the fundamental bias of how our brains work then limit or prevent us from solving fundamental problems in physics beyond a certain extent?

2. Feb 19, 2016

### Staff: Mentor

It is different because there is only one time dimension and because its signature is opposite that if the space dimensions.

3. Feb 19, 2016

### sanman

Hi, I'm sorry if I'm sounding like a pest - but WHY is it that way? Why is there only one time dimension, and why is its signature the opposite of the space dimensions? What do you mean by signature -- just some + or - sign that flags it as different? What is the physical underpinning for these differences?

4. Feb 19, 2016

### Staff: Mentor

Science is notoriously bad at answering WHY questions. All it can ever do is to point you to another theory, which we don't have in this case.
In relativity spacetime is described as a pseudo Riemannian manifold. One characteristic of a pseudo Riemannian manifold is its signature. In the case of spacetime that is (-+++). The order doesn't matter, what matters is that there are three of one sign and one of the other sign.

5. Feb 19, 2016

### Staff: Mentor

My original point about the signature is essentially to point out that this statement is not correct:
The fact that there is only one time dimension and that it has the opposite signature is what sets time apart from the other dimensions in spacetime. Physicists also have daily lives and experience. The model accounts for our experience by the signature.

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