The Fabric of the Cosmos

[maddownunder]

I'm reading Brian Greenes' "The Fabric of the Cosmos" and I'm about a third the way through it. So he's up to to talking about and dealing with Time. This whole issue of what time is, is really giving me the S**ts ! The topic deals with why time seems to flow only one way, despite the fact that mathematically and that the theories of Relativity say the processes can go forward or back. He uses the analogy of an egg rolling off a kitchen bench, and how come we never see it unsplatter, reform and un-fall back up on to the bench.
To my way of thinking, even if you could run time backwards. Why would the fundemental laws of nature stop working the the way they appear to have done up to the present time. Seems to me the egg cannot know about time, all it can know is that is pulled towards the center of the earth by gravity. My thing is that every event or occurance in the Universe, no matter how big or how small, is a result of a series of events governed by a force(s) of nature i.e Gravity, Electromagnetism, the nuclear forces etc. etc. That time itself it not a force, and brings nothing to the understanding of the make up of the elements in the universe, or mechanisms behind the events we see in the universe. I don't understand why it's even a question in the physics world. Or am I just

[BerrieK]

Aah but time and space go hand in hand...our understandings of space are connected with gravity, even down to apparent gravitational effects of dark matter on visible matter...so without gravity there is no space and if there is no space there is no time...if you COULD indeed run time backwards would events that have occurred in the time that we percieve be undone (I think not) or rather would we interact with the backward time in another way that science has not yet though of a name for (other than plastic surgery). If time were backwards then perhaps the fundamental laws of nature would indeed work differently as space and gravity may also be altered.

[xelasnave]

I can not see the relevance of time in some respects.

Space time for me describes space via human geometry without coment upon the physical make up of space... and I point out that I am talking from the view of an ignorant layman and standing outside a house does not allow one to understand what may go on inside same...

still it seems to me that gravity has been linked unnecessarily with time in the hunt for an understanding of gravity...

I have not even seen the equations (11 I think setting up for GR) but I already suspect that time crept in via the principle of equivalance... which relates gravity to humans sums and human experienence in a quantifiable state for contemplation on a 2d sheet of paper... and that is great that is a big achievement of that there is no question...

but still do we need t in the mix one wonders...GR would not work I guess without it...

T is necessary for humans and it seems that the Universe includes T in things... simply time means everything does not happen at once...which one would imagine would be the case of no time...mmm...but does gravity worry about T ..it does what it does at the fastest speed in the Universe C so does graviy need to know about time??

But maybe we leave T in general relativity for the moment .

alex

[xelasnave]

If there is anti matter and given the relationship between matter time and energy can there be anti time ... and if there could be what properties would it exhibit?

alex

[maddownunder]

If time is a concept and nothing more, it would seem to me to be impossible to have anti-time. Time to me isn't a force like gravity, it isn't matter like an atom or proton, or even a photon or electron. The only use I see for time is it provides a meathod of allowing us to calculate specifics about the way the universe work and about characteristics of things within the universe. But I can't imagine that if we lost the ability to precieve / measure time, that the univsrse would grind to a halt.


If you freeze water into an ice cube, then let it melt again. From the ice cubes point of view, how can it tell if it has gone from water - ice - water, forward in time. Or if it has gone water - ice then gone back in time from ice to water ?

[xelasnave]

But time in fact has little to do with what you describe and I would suggest it is the change in temperature that changes the condition of the water/ice and not the passage of time. If the temp does not change it matters not how much time passes the condition of the ice or water will not change ...until the temp changes.

alex

[sjastro]

The direction of time is important in thermodynamics particularly the second law which states the entropy of a system not in equilibrium must increase.

A practical demonstration of this law is that heat flows from a hot body to a cold body.

Violating the second law by reversing the direction of time leads to a major paradox:- the perpetual motion machine.

Regards

Steven

[xelasnave]

Originally Posted by sjastro

The direction of time is important in thermodynamics particularly the second law which states the entropy of a system not in equilibrium must increase.

A practical demonstration of this law is that heat flows from a hot body to a cold body.

Violating the second law by reversing the direction of time leads to a major paradox:- the perpetual motion machine.

Regards

Steven

My father cursed me by telling me no one could invent a perpetual motion machine... it started me inventing... thats how I stumbled on the concept of an electric motor as a kid....

The words always bring a smile Steven because they explain so much to me about my approach to things.

alex

[GTB_an_Owl (Geoff)]

Steven - i have a question

why does the "heat" flow TO the "cold", and not the other way round, or an equal reaction between both ?

geoff

[bojan]

Originally Posted by GTB_an_Owl

Steven - i have a question

why does the "heat" flow TO the "cold", and not the other way round, or an equal reaction between both ?

geoff

Perhaps I may try to add to answer to this question (because Steven already answered):

Originally Posted by sjastro

The direction of time is important in thermodynamics particularly the second law which states the entropy of a system not in equilibrium must increase.

A practical demonstration of this law is that heat flows from a hot body to a cold body.

Violating the second law by reversing the direction of time leads to a major paradox:- the perpetual motion machine.

Regards

Steven

It is because of entropy (this is a measure of disorder of the system), something that always increases and never decreases in a closed system.
Actually, we can decrease it, but to achieve this (increase the order of the system) we have to add energy to the system.

Now, because the temperature is actually the average kinetic energy of the particles of which matter is composed, it is not hard to imagine what is happening here.
Lets say that we have a cube of something (made of atoms, of course) and lets say that the temperature of this cube is 0°K, absolute zero. That means the atoms will be perfectly still.
Lets imagine now that we have another cube, same size, of the same material, but at some temperature, lets say 100°K. And those cubes are now touching each other.
What will happen at the atomic scale?
"Hotter" atoms at the boundary will start to bump into "cold" ones of the other cube and in elastic collisions they will transfer some energy and momentum to them. They will slow down. The layer of atoms deeper in the hot cube will then start to transfer their energy to the slower ones.. etc.
After some time, all atoms of those two cubes in contact will have the same average speed and therefore kinetic energy and the temperature of both cubes will be 50°K.

The heat was transferred from hot body to cold one.
The energy was transferred from hot body to cold one.

The measure of disorder (entropy) of this system was increased - because two cubes of different temperature in contact is very organized system. Two cubes of matter in contact and at same temperature is very disorganized system.

Is it possible to "suck" heat from one cube and "store" it to another?
Yes, but we have to put energy into that system. With Peltier element for example. The energy will come from power supply current.
But for something like that to happen spontaneously, the odds are very, very, very small.

In other words, all this is because of statistical nature of behaviour of huge number or atoms.....

I hope this explanation will help you :-)

[GTB_an_Owl (Geoff)]

sounds like a "one sided argument" to me bojan - and the fella on the "HOT" side "loses" every time


or does the other fella "gain"

Hi Alex


geoff

[sjastro]

Geoff,

Bojan has explained it well.

Here's a practical demonstration of the second law.

Suppose I heat a metal ball, refrigerate another and then bring the two in contact to form a thermodynamic system.

Initally the system is in low entropy or organized because there is a temperature differential between the balls.
To keep this system in low entropy or even increase the temperature differential I need to supply energy to the system by heating up the hotter ball and cooling down the cooler ball.

This is an example of an open system as the energy sources are external.

If I disconnect the energy sources, the system becomes closed. If thermal equilibrium isn't reached or the temperature differential increases (cold flows to hot), the implication is that the closed system has created energy out of nothing which is a violation of the conservation of energy.

The dreaded perpetual motion machines "operate" on the same principle of creating energy out of nothing.

Regards

Steven

[bojan]

Yep..
Fella on the hot side ALWAYS loses.. energy.
But the whole thing gains entropy. So here you go.

[xelasnave]

Here is something on time travel

http://www.sciencedaily.com/releases...0822164415.htm

alex

[maddownunder]

Originally Posted by sjastro

The direction of time is important in thermodynamics particularly the second law which states the entropy of a system not in equilibrium must increase.

A practical demonstration of this law is that heat flows from a hot body to a cold body.

Violating the second law by reversing the direction of time leads to a major paradox:- the perpetual motion machine.

Regards

Steven

Is time not the unit of measurement for any given series of events ? I don't understand why it is that there seems to be a perception that, the events being measured would cease to occur if we stop measuring them. We only measure them in reference to another event anayway i.e one rotaion of the earth.
I would say that the second law of thermodynamics is the result of atoms that have been energised above their normal state or below their normal level of internal energy, dissapating the additional energy. Time does not force the energy out the atom or lock it in there. The atom or molecule just has a natrual state of equalibrium and will allways try to return to that state, and that goes for every single molecule, atom, nuetron, proton, quark etc. etc. To me these events are not governed by our comparrison of how many times event X occurs compared to event Y.

[sjastro]

Originally Posted by maddownunder

Is time not the unit of measurement for any given series of events ? I don't understand why it is that there seems to be a perception that, the events being measured would cease to occur if we stop measuring them.........

In the subatomic world that's what happens. In quantum mechanics an unmeasured state is a superimposed state of potential outcomes. When we measure or observe the state we obtain a particular outcome.

A variant of the Heisenberg uncertainty principle is the energy time equation:

Delta E X Delta t ~ H (Plank's constant.)

When a particle decays the amount of energy emitted is a function of the time taken to go from one state to another. Since it's a quantum process if we happen to change the time interval the decay process will not occur as the emitted energy will change.

Regards

Steven

[Max Vondel (Peter)]

Just a quick comment on the nature of time. Even though time seems to flow; ie seems as a stream, it is better thought of as a quanta. At the very smallest scales time appears as discrete jumps just like the quanta in planck's constant. Once you add a direction of causality to elements of quanta of volume space and time, we are able to derive all the elements of a quantum and relativistic principles from first hand. That means we have a theory that predicts the master elements of the universe based on pure mathematics and logic alone. All we observe falls within this framework. We are on the verge of understanding the mind of our creator GOD mathematically and logically. QUANTUM LOOP GRAVITY AND CAUSALITY FOR EVERYONE !!!!

[g__day (Matthew)]

Quantum theory surprisingly helps here, without causality (time flowing in only one direction) it can be shown most models of creating a universe from a big bang + inflation physics leads to a tangled mess (Scientific America July 2008).

Relativity and Newtonian physics really deal with properties of matter and energy within the fabric of normal spacetime - not the meta rules that must be present to shape the underlying properties of spacetime itself (such as its topology and causality).

[xelasnave]

Hi Peter... you said the magic word...gravity...if you understand quantum loop gravity I would really appreciate an explaination is simple terms that I may comprehend... gravity fascinates me and I like to heoar about any approach I can find..
alex

[bojan]

There is no simple explanation for what you are asking, Alex...
You have to either accept what physicists (and by that I mean so called main stream) are saying, or you have to embark on very hard and long voyage of educating yourself in fundamentals of math and physics, to be able to comprehend what it is all about. Otherwise there is no point...