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 :screwy:

[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:P.

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:eyepop:...which one would imagine would be the case of no time...mmm...but does gravity worry about T:D ..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 :lol::lol::lol:.

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:eyepop: and I would suggest it is the change in temperature that changes the condition of the water/ice and not the passage of time:D. 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]

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]

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]

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





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]

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


or does the other fella "gain" :whistle:

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/2007/08/070822164415.htm

alex

[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. 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]

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]

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]

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...

[bojan]

I feel that I should explain my statement above (about mainstream scientists) in more detail..
I am not against "revolutionary ideas" in science per se..
The problem is the presentation of non-mainstream issues. This presentation is in almost all cases over-simplistic, giving the general public a totally wrong idea about how new things are come-to be.. like, someone has to simply scrap everything that has been done in the past (because it is old and wrong and part of scientific establishment etc) and voila! Now we know the REAL truth!..
Nothing can be more wrong that this..

Main stream science is a result of HARD work of generations of scientists, a process in which ideas are checked and cross-checked millions of times for interrelated consistency with other related and non-related facts and theories.. Rejecting main-stream science means not using pre-existing knowledge.. and this is very unreliable thing to do.

Presenting ideas that are not peer-reviewed properly as some sort of "revelation" is dangerous (because if idea or theory is not checked, how do you know you have not made a fundamental mistake?).
And, if that idea does not pass peer review, it does not mean the "official" science is against it because of conspiracy or some like that reason.. It is because the idea itself has no merit.
This is how science works.

[xelasnave]

I do read stuff and although somewhat flipant about the math can assure you I am aware of my limitations however when one has the wonderful resource of the net available it seems stupid not to take advantage of all that is available.
I have probably boasted about it many times but I was not bad at chemistry ..could do leaving certificate chemistry when in 5th class and I always liked physics and the laws is sets out.
Math is only a problem for me because I am lazy and learning it is not easy for an old man... a mate sent me an e book on calculus and I have read it.. he wanted me to do all the problems but I have not and it is just lazy I know.
I read many maths sites only to understand the many disiplines in the field...and that amazes me..so many principles... just the headings runs for pages.

But I have no plans to seek work as a scientist or go for a degree to show I care... but it is all so interesting... I mean gravity that is so fascinating for me... and in truth I see no one has answered enough questions to unify it with the other forces.

I follow the lives of many scientists and they are my heros ... they take us out of the darkness (except those who present us with black holes, dark matter and dark energy:lol::lol::lol:) and the stupid superstitious ways of our past.

We are very lucky to live in an age where reason commands respect and religion and vodoo are not the norm.

Thank you for your reason :thumbsup:

alex:):):)

[g__day]

New Scientist has a great article this edition that looks at the current models theoretical physicists. In essence it repeats what I have said above (no I didn't read it first).

Basically

1. Einstein had horrendously complex equations to solve in relativity
2. He imposed two field constraints to solve them - he said on large scales the universe is homogeneous and isotropic
3. The background radiation studies COBE - and SLOAN Sky surveys shows us that the homogeneous call isn't too bad (although galaxies right up to super clusters tend to show a surprising fractal structure out to a range where they shouldn't (no organising force should have been able to propogiate to 1 million light years or beyond to enforce such observed structure)
4. Examine of type 1A supernovae - a standard candle - showed the Universe appears to be must bigger than we though, especially at far distances - implying if Einstein's two constraints are correct the expansion of the Universe must be accelerating in the last few billion years
5. Dark matter and dark energy are suggested as altering mechanics to this framework to allow it to fit with what we see without changing the underlying model and its two constraints.

The misfit is so large, the basis for the two initial constraints are so arbitary and the lack of a clear model that encompasses dark matter and forces is so vague that a serious group of high end theoretical physicsts are questioning these two initial constriants - asking what slight (or large modification of them) would give us what we observe today with minimal disruption to the standard models and relativity.

Turns out one small change to isotropic would account for what we see without the need for dark matter or energy. Our Hubble sphere is not common and representative - its a bit of a bubble, or put a common way its an underweight weakling (density wise) and its surrounded by more massive, (and more representative of the average density of the entire Universe beyond what we can see).

So if our corner of reality is lighter than average - no need for exotics - gravity drag of the rest of the universe beyond our bubble would explain what we see with conventional physical frameworks.

I like simpler over complex!

[xelasnave]

Sorry Bojan I missed this..it is very busy here today.. but not so busy I cant get my teeth into this.

You said

The problem is the presentation of non-mainstream issues. This presentation is in almost all cases over-simplistic, giving the general public a totally wrong idea about how new things are come-to be.. like, someone has to simply scrap everything that has been done in the past (because it is old and wrong and part of scientific establishment etc) and voila! Now we know the REAL truth!..
Nothing can be more wrong that this..

Now this is a fair generalisation I agree but the fact is often something very simple will need much explaination... no matter what..in truth everything is so very complex.. and if there is any issue I have with the exactness and infalibity of math is not in the science of it but in the difficulty many have in applying it... I have often sited the Greeks explaination of why the planets wandered about..they had the planets moving around the Earth in circles... as I understand the math of this expalination was flawless.. but they were absolutely wrong...


You may recall the chap who stood up and said stomach ulsers were caused by a bacteria..he stumbled on the idea from researching old treatments..he found that once they were treated with bismuth..and he followed up on why that may work and arrived at the notion it was bacteria...well everyone in the field said he was an idiot..particularly the well establishe Macquarie street specialists who held onto the old idea...they were expert after all..but they were wrong.

And so I say how many tests and studies that supported the notion that ulcers were stress related were published, how many patients could be used to support this idea that it was stress.

In spite of how I must present as somewhat casual I am very careful as to what I accept... if I hear about something new the first thing I wonder about is their authority...how do they know this to be so and I have no problem with sample upon sample test upon test to evidence the premise suggested.

ANd I agree science must be done this way... otherwise anyone could claim anything...particularly with medicines etc.

I think similar examples to the Greeks mistake and the Macquarie Street specialists can be found if one cared to look thru the ages...
So many medical truths of only a few years ago are now mere wives tales...

You said

Main stream science is a result of HARD work of generations of scientists, a process in which ideas are checked and cross-checked millions of times for interrelated consistency with other related and non-related facts and theories.. Rejecting main-stream science means not using pre-existing knowledge.. and this is very unreliable thing to do.

[xelasnave]

sorry I hit the post key but there is more to come
alex

[g__day]

LQG - outlined well here http://en.wikipedia.org/wiki/Loop_quantum_gravity and here http://relativity.livingreviews.org/Articles/lrr-1998-1/

Briefly it tries to propose a classical framework to understand gravity, or more correctly quantum gravity. To do this it imposes both time and space are quantised at the smallest level - Planck units. Doing this satisfies some frameworks it must be validated against, but it makes no predictions outside of the standard model - so it can't be validated or denied. Trying to do so is extremely challenging mathematically. Getting it to agree with several major validation points from other theories (must pass tests) requires you to set parameters a certain way (without these constants being derived from fundamental constraints) so to make it work is variable. The field it encompasses too is so broad there is an over-abundance of topic areas to try and study and resolve.

Too it assumes spacetime has a lower limit without explaining why - which is rather a dubious concept. To fully understand it - well it gets abstractly tough really fast, with field effects and very high order maths (very, very high order).

[xelasnave]

I dont think I hit the post key this machine has a problem and it is not me...anyways to continue and to comment upon the last bit....
I agree about the benefit of accumulated knowledge the process and fitting an idea into what is currently known....no problems there...

However take gravity..just as a random thing to mention...

The current work is going nowhere ... the cutting edge stuff on gravity does not mean sqwat... now I dont know everything that is going on but despite years of looking at and asking the question...what is gravity I find no answer...

It is nice we have general relativity and it may or may not work... I dont really know but the premise that space respond to the sums as if the sums demand certain actions from space is nonsence... general relativity is a geometry that seeks to measure and set limits of movement (as far as I understand it and that does not mean that I understand it..I dont think many do understand it but unlike me they wont say zip..they are afraid to challenge because they may seem stupid) well if my ideas are stupid they will die so my stupidity does not cause general relativity to quiver...still all we have as to gravity is geometry..string theory is little more..as far as I can tell it is more geometry...and that is all very fine to set boundaries but it says nothing about what is really going on... I can not accept that space time is there because a man invented it..there is more to it and this dogged determination to use that model for gravity is holding up unification of the forces in my view.... and the man who came up with the idea DrA the man most likely to suceed in unifying the forces because he had a running start failed..well in my view you will never fit gravity into the mix while science refuses to take time to ask ...how does it work... no one knows how it works...and until we know how it works I doubt if the forces can be united... mind you I can:lol::lol::lol: but I am just a mug and therefore anyview I have will be crackpot...that does not mean I am wrong..it does not mean I have not had a magic insite other have not... well others have had my insite as we know....

Still when they threw out the eather any attempt to suggest a particle flow necessary for the environment I suggest was gone... and now what do we know about space...it is not that empty..it does have billions of particles flying about from all over..yet we can not admit that this comes close to the concept of an eather..well what is it..what better word than eather to describe what we know to be there...

and this leads me to your statement.........
This presentation is in almost all cases over-simplistic... well I suggest that to throw out the concept of an eather upon one experiment such that the issue was never raised again was stupid... now look at the gravity b probe mission..what does it do if not the same as the MM experiement... it ssaid was not on.... dont dismiss what I say as silly but please think about the parrallels of the two...and I know this will have folk jumping on fine points but I simply say if frame dragging is presenting such a challenge to establish with sats at various spots in space why would an Earth bound experiment be able to find esentially what the gravity b probe is trying to establish....

It seems as if there is a determination to make general relativity work for gravity no matter what and it seems it may not be the final answer and I am not the lone voice on that...

AND to me there are so many folk in the established world of science who just talk crap... I know that journalists are to blame but they got their stories from someplace...just look at the crap that goes with black holes..so much belief as oppossed to reliable observation I feel...

The only critism I have of current scientific method is the prediction part.. now that sounds reasonable but it has people expecting to find what they are looking for... take cosmic background radiation..there is no other expalination and none will be considered simply because it was expected so any alternative ideas do not get off the ground.

Look at DrA he had his cosmological constant which he threw out when Hubble suggested the Universe was expanding... at that point even Dr A believed the Universe was static..but one new find and he changed direction... now I dont know if his approach was valid or not but there are those today who feel he was right.. but he seems to have concluded something about space that seems to be holding true..if it is there that is..dark energy.

I have been a worker and I have been closer to the top and if there is one thing I know..not everyone is truthful and even the best experiments can be fudged so although science is initself infalable humans are unfortunately not always so... and so the will be science that has been corrupted to suit the motivations of those invloved... I dont know if it has ever happened but I could imagine a researcher fiddling the books to get a grant or impress a girl..stuff like that happens...and so I believe little... that does not mean I am stupid and closed to ideas it just means I dont buy everything that is on the table because it is popular with others.

Sorry to be so brief on a matter that deserves much more input but I feel as we have chatted in the past you can forgive my slackness and brevity.

alex

[xelasnave]

I am accussed of simplifying my ideas and leaving bits out but I am not the only person guilty of this and I take the above as support for that assertion.
I just leave more out than most. But I always try to keep things simple..they either make some sence or not and I am sure that almost any proposition can be supported or torn down with math.. and we see the importance of small variations accept them move on and yet can not accept a general premise may be flawed even though it has been in use for decades... ulcer example for example.

In my view what we are trying to explain is so complex that the greatest expressions of math will never expalin the complexity such that we can have any reasonable comprehension.


alex:):):)

[xelasnave]

Great link..lots of blue bits which is good....but I have no idea what it is that is established..it seems like more geometry offerring little in understanding of what gravity is.... I will take it that it is just me..but I dont see anything in it that tries to take the matter further just makes it more conveluted...

Still I will not give up...back to the blue bits:whistle:

alex:):):)

[sjastro]

Homogeniety and isotropy are not restraints but postulates for cosmology. Changing the isotropic nature, essentially destroys the mathematics of space-time expansion.

(http://en.wikipedia.org/wiki/Friedmann-Lema%C3%AEtre-Robertson-Walker_metric).

The RW metric extends outside the Hubble sphere to the entire Universe. So even a slight change to isotropy (what ever that means), brings down the entire model.

As the Hubble sphere is the observable Universe, we cannot make any comparisons between what is inside and outside the sphere. Anything outside the sphere is pure speculation.

Seems we are making the Universe more complicated.:)

Regards

Steven

[g__day]

Steven

Largely agree - there are unknowns and science is questioning are they in the right place. I say constraint - you say restraint - toss you for the semantics, but in essence yes - modify isotropic and your expansion is merely a bubble swelling in a larger context than we can view.

But it goes deeper than that - it means everything we hold as a constant - is really a property of the local framework - and not representative of the Universe as a whole. That actually appeals to me - the local geometry being variable due to density fluctuations from the Big Bang causing changes that set in stone our Hubble Spheres relativistic constants based on the topology of the local framework.

Until it can be tested with evidence - its an intriguing theory to be counted or rejected. Let's see where it goes as time, research and evidence mounts for or against.

Alex

No one promised simple when it comes to understanding theoretical physics, and spacetimes interactions at a quantum and relativistic level with baryonic matter and energy. You don't get more abstract or challenging than that - so one can't cookie cut it beyond the real basics. GR has been well proven by over 32 independent tests - and the constancy of the speed of light has been check by those same tests to over 18 digits of accuracy - so it is only our most precisely checked constant todate.

Whether you wonder if gravity its a property of the framework itself, the framework interacting with energy and matter within it or a different kind of force - studying it at a classical, relativistic quantum or SuSy level simply isn't easy today - but I encourage you to ask and question as you do. Like the X files - the truth must be out there!

Matt

[xelasnave]

Thank you Matt I just want to know everything and get frustrated I can not:lol::lol::lol:.

I thought today what I am trying to say really (without putting to fine a point and to be taken a very ruff generalisation)...is that space time describes space and/but space must be of a physical make up. Sounds simple when I put it that way.. Somehow it may be the eb and flow of all the particles that make up space that is described by space time..
I dont think GR is wrong when I think it thru I just think by not understanding the nature of the space all the forces can not be united... my frustration is best described that way..as best I can tell.

Thanks again for your help and undersatnding.

alex:):):)

[xelasnave]

Also I have no problem with the speed of light by the way but was curious about the way they worked it out.
Alex

[g__day]

The speed of light in a vaccuum I always think of as the tension of spacetime - like plucking a guitar string - hard or soft doesn't matter - it will vibrate at only one speed for a set tension.

The speed of light can be directly caculated from Maxwell's equation (its a page of tricky maths) http://www.phys.unsw.edu.au/einsteinlight/jw/module3_Maxwell.htm

But that is a very powerful proof when that field property can be directly determined by the key forces shaping the field itself.

PS

Apologies above - mis-spoke its Homogenity, not Isotrophic behaviour that science is questions - still around we could be in the middle of one or more "voids" (low density areas) around 300 million light years to 2 billion light years diammeter. Tests based on COBE in the next decade with more sensitive space telescopes might rule this model in or out.

[sjastro]

Sorry a typo, I meant constraint.



Apart for violating isotropy, there is no reason why local geometry should be any different. The Hubble radius for any observer in the Universe is 13 billion light years. Space-time within this radius is spread out to obey a flat Euclidean geometry.

The use of non Euclidean geometry for space-time is very much a localized phenomena for high gravitational potential objects such as neutron stars and black holes.

For anything else flat space is a good approximation.

I'm afraid I can't see how sitting in a void actually increases the velocity of space time expansion. Low density or no density will retain the inertia effect of the BB, in which space-time expansion proceeds at a constant velocity.

Regards

Steven

[sjastro]

Alex,

I'm afraid it doesn't:).
A common error is to think that properties of space are equivalent to those in space-time. They're not.
That's were all the confusion begins, from space having a boundary to equating a galaxy's recession velocity with it's velocity through space.

A very simple example is the property of volume. Volume is a property of 3-dimensional space but not 2-dimensional space. It's area.
Similarly time and distance in space-time have different meanings to time and distance in space.

For example the formula for the separation of 2 points (A and B) in space is simply:

dS^2=dR^2 dR is the spatial separation.

Compared to the separation of 2 points (A and B) in space-time.

dS^2= (C X dT)^2- dR^2
C is the speed of light, dT is the time interval, R is the spatial separation.

It doesn't end there, the pathway of a particle in travelling from A to B needs to we defined.

If a particle travels from A to B and dS^2=0, the particle is a photon.

If a particle travels from A to B and dS^2> 0, the particle travels on a time like path and causality is not violated.

If a particle travels from A to B and dS^2< 0, the particle travels on a space like path and causality is violated. (It can travel faster then light.)

As you can see the space-time is much more complicated to deal with than space.

Regards

Steven

[xelasnave]

Thank you Steven thank you for taking the time but I confess I feel I have a less than secure grip on all of this..

alex

[bojan]

Here I go again...



But, do not feel bad about it.. I must say for myself that I personally do not understand 99.9% of this stuff properly.
That is why I follow my own recommendation (in the quote above). And I try to educate myself, whenever I have time. This is the only way to understand more, and correctly..
Today, life is simply too short for individual to know everything.. And it will be even much worse in the future.
That is why we sometimes simply have to believe in a system..... however bad that may sound to you.

[bojan]

In the process of my own education, I found this website:
http://people.cornell.edu/pages/jag8/index.html
However, and again, the proper understanding of all this requires the solid comprehension of math tools. But, we have time.. no rush... Important thing is not to create a wrong picture in our minds (for example, something like gravity does not suck)

[xelasnave]

Bojan said........

That is why we sometimes simply have to believe in a system.

OK but you know the one I will believe in...push gravity of course:lol::lol::lol: because at least I understand what I say about it, and as I seemingly may be the least crackpot of those who "push" the idea I feel that entitles me to claim highest authorty in that field...if nothing else I have probably rattled on about it more than everyone else from Le Sage to Wright.

I do believe in most stuff but I need to understand why... it means a slow learning process at best and at worst no learning process at all... still I so enjoy the ponderings.. it sure beats hanging around with girls:lol::lol::lol:

You are a gentleman and I scholar Bojan and I do believe if on nothing else I am at least correct on that one.

Thank you.

alex:):):)

[bojan]

Alex, I think you are grossly mistaken about those two items above ;)

[xelasnave]

Now I cant be wrong about everything:whistle:.
alex:):):)

[g__day]

Being in a void confuses the local versus universal seperation rate and local expansion (recession velocities) in their models. Frankly I think its a strech (pun not quite intended). Recession velocities due to an expansion of space time can only occur in non gravitationally bound regions. I think their thinking is a lower mass volume would have a different (higher) expansion rate as it would have a lower gravitational well to slow expansion. At under $7 its worth a read.

Personally I think all space time being the same in all directions at a large enough scale is a bit arbitary. But I have no thoughts on how much variation could exist nor what gradations would be needed in a model to compensate. But if large difference did occur this might possibly re-shape the topology of space time (in a way that necessiates more than a flat Euclidian model). Its doubtful in my mind that this last part would be true - but should be detectable so it could be tested simply to be ruled out.