SUPERNICHTS?

[Aguirre]

Let me start with a simplequestion.

 

Why we can not see intothe future

 

but it is the only way wecan go, why we

 

can see the past but thereis no way to

 

go back?

 

 

 

 

 

[IM Egdall]

We go but cannot see into the future because of the arrow of time. The arrow of time is what brings us from the present to the future. And no light from the future reaches our eyes because it has not been produced yet, so we do not see into the future. (What exactly causes the forward arrow of time is still somewhat of a mystery in physics.)

 

We cannot go but can "see" into the past because of the finite speed of light. We see when light from an object reaches our eyes. SInce this takes a finite amount of time, we see objects as they looked in the past.

Edited August 8, 2011 by I ME

[Aguirre]

We go but cannot see into the future because of the arrow of time. The arrow of time is what brings us from the present to the future. And no light from the future reaches our eyes because it has not been produced yet, so we do not see into the future. (What exactly causes the forward arrow of time is still somewhat of a mystery in physics.)

 

We cannot go but can "see" into the past because of the finite speed of light. We see when light from an object reaches our eyes. SInce this takes a finite amount of time, we see objects as they looked in the past.

 

 

 

So the arrow of time makes us going in the one way

direction future.

But it does not explean why we can not see in this

direction. Where yet nothing is you hardly

can observe something.

There is no space-time structure in the future cone

in the Minkowski space.

But if you look into the night sky you will see

space-time structures, occupied space-time structures.

Occupied by space- world time.

By the way how you explain the non- equilibrium state

of the universe?

 

496=496

 

In der Ruhe liegt die Kraft

 

Sig

[Aguirre]

What has the entropy, the scale factor and time in common?

And what not?

 

496=496

In der Ruhe liegt die Kraft

Sig

[csmyth3025]

Perhaps my understanding of entropy is too simplistic.

 

For instance, suppose you take a tub of water with a partition down the middle and put hot water on one side and cold water on the other. If you put the "hot" end of a Stirling engine in the hot water side of the tub and the "cold" end of the engine in the cold water side of the tub you can run the Stirling engine and do nifty things like blow air on your face with a fan blade attached to the shaft of the Stirling engine. Once the temperature of the water on both sides of partition equalizes, though, the Stirling engine stops working. It can no longer extract any more energy from the tub. In other words, the entropy of the water in the tub has reached its maximum. This does not mean that there is no more energy in the water in the tub - there is no doubt lots of (thermal) energy still contained in the tub, but we can no longer extract any more energy from it as a closed system in order to do any work:

 

Entropy is a measure of how evenly energy is distributed in a system. In a physical system, entropy provides a measure of the amount of energy that cannot be used to do work.

(ref. http://en.wikipedia....tion_to_entropy )

 

In the far distant future, when thermonuclear reactions have ceased, the universe is filled with a uniform and gradually cooling radiation background and all gravitationally bound systems have either collapsed into their most compact form or dispersed due to the expansion of space, the world as we know it will have reached a stage of maximum entropy. The total amount of energy in the universe may still be very high (perhaps the same as it is at the present time), but there will be no energy available to do things like make new stars or power active galactic nuclei. This would be the so-called "heat death" of the universe.

 

As far as I know there isn't any way to reverse this trend. It's a one-way street. The arrow on the street sign pointing in the direction that everything is going is the arrow of time.

 

Chris

[IM Egdall]

I think Chris said it correctly. The only aspect of the laws of physics that tells us why the arrow of time in our universe is in the forward direction is the second law of thermodynamics. And the universe is evolving to higher and higher entropy.

 

Wikipedia quote:"second law of thermodynamics is an expression of the tendency that over time, differences in temperature, pressure, and chemical potential equilibrate in an isolated physical system. From the state of thermodynamic equilibrium, the law deduced the principle of the increase of entropy and explains the phenomenon of irreversibility in nature. The second law declares the impossibility of machines that generate usable energy from the abundant internal energy of nature by processes called perpetual motion of the second kind."

 

I suggest reading Brian Greene's wonderful book, The Fabic of the Cosmos. It tells the entropy/arrow of time story in plain English.

Edited August 31, 2011 by IM Egdall