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Why does time require matter ?

by phinds
Tags: matter, require, time
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salvestrom
#127
Jan31-12, 07:47 PM
P: 226
Quote Quote by Chronos View Post
Since light and gravity propogate at the same velocity, if you can see a star the gravity of that star is tugging at you. Given that gravity is treated as the curvature of spacetime under GR, spacetime is curved. Assuming you could find a place in the universe where no light had yet reached, there would be no gravity hence no curvature. We can see the light emitted by the surface of last scattering [CMB], so it would appear such a place does not exist in this universe.
I totally accept the statements you make - I realised this in another thread on redshift. But such places are as free from gravity as anywhere you're going to find. The curvature is surely so minimal as to be negligable? Also, such places are expanding. Won't this be negating gravity? Flattening spacetime?

Not to be picky, but I assume you meant observable universe at the end there? =D
budrap
#128
Jan31-12, 09:42 PM
P: 40
Quote Quote by Chronos View Post
Since light and gravity propogate at the same velocity....
That is a theoretical statement only. The speed of gravity has never been directly measured.

http://math.ucr.edu/home/baez/physic...rav_speed.html
Chronos
#129
Feb1-12, 01:16 AM
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Kopeikin and Formalont claim to have measured the speed of gravity in 2003
http://www.csa.com/discoveryguides/gravity/overview.php. This finding has been challenged by several scientists [including Steve Carlip], but, Kopeikin has vigorously defended the study [e.g., http://arxiv.org/abs/astro-ph/0311063]. The newtonian view was the speed of gravity is infinite, but, I doubt any mainstream scientist takes that seriously anymore - albeit some 'fringe' personalities [e.g. Thomas van Flander] have argued the case. I don't recall anyone claiming it was slower than light.

PS Yes, I intended the observable universe. I tend to refrain from invoking the unobservable universe[s]. The important point here is that gravity, like light, permeates the entire observable universe, hence some amount of spacetime curvature is present everywhere in the observable universe. While it is obviously miniscule in intergalactic space, the extent of curvature is irrelevant within the context of this thread.
salvestrom
#130
Feb1-12, 02:53 PM
P: 226
I draw a lot. Line work. That's just pencil on paper. A line image has a lot in common with the universe. The graphite markings can be mass and the unmarked paper is spacetime. It can be realised that both are needed to complete the picture. Without the blank page seperating the lines we have a single blob of grey. Without the lines we have an undefined blank page.

It initially seems that the blank page is far less affected by the absence of the lines than vice versa. I currently own an utterly untouched sketchpad. It hasn't ceased to exist because it hasn't been drawn in. It's still a sketchpad. If only in potential. As for spacetime, in the absence of mass or energy, it will just sit there, uncurved, unloved, writing songs any emo goth band would be proud of. But the undefined blob of matter has almost no physical definition. It has no length in any direction and no time passes. It is missing two of three basic quantities with which we define much of the universe. While the spacetime is missing only one.

I'm biased. While open minded to a number of odd possibilities, I increasingly lean toward the notion of spacetime as being utterly fundamental to everything, and not something to be sidelined. The above paragraph might seem to support that particular personal Pisa. And yet a philosophical tone in this post and in my own mind, which seems hard to resist, points out that these three things belong together and are as insperable as spacetime was for Einstien.

So, perhaps my answer to the OP's question is that time doesn't require matter... but the universe - and my artwork - is a lot more interesting when all three are around. =D
phasl001
#131
Feb20-12, 05:02 PM
P: 4
So back to the subject, time doesn't require matter (as it is considered a dimension). It will exist as long as the universe creates it.

-Phil
phinds
#132
Feb20-12, 05:10 PM
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Quote Quote by phasl001 View Post
So back to the subject, time doesn't require matter (as it is considered a dimension). It will exist as long as the universe creates it.

-Phil
Welcome to the forum.

You have expressed an opinion as a categorical statement of fact. Do you have any physics to back it up? This forum is not big on unsupported speculation.
salvestrom
#133
Feb20-12, 06:31 PM
P: 226
Quote Quote by phinds View Post
Welcome to the forum.

You have expressed an opinion as a categorical statement of fact. Do you have any physics to back it up? This forum is not big on unsupported speculation.
Let's be fair. The poster may not know they are stating an opinion. Part of the point of the forums is to smooth over the gap between media interpretation/spin of science and, well, science. Joke incoming, do not read if allergic to humour: media spin is a spin-∞ particle. It's always changing and never returns to the original form, regardless of how you turn it. One must acquire knowledge of the original state of the system to learn anything. ;)

Time is either a proper dimension or not. The 'not' covers a range of possibilities, perhaps, but currently maths treats it as a pseudo-dimension. It works to do so, but there's no actual reason, just based on that maths, to catagorically state the case either way.

As a proper dimension it makes things rather neat and tidy, which is great. Symmetry is neat and tidy. But that doesn't mean the universe will oblidge.
phasl001
#134
Feb21-12, 10:26 AM
P: 4
Time is a dimension. In theory (One that is widely accepted), space & time is the fourth dimension mentioned by Albert Einstein. In our Universe, which was created perfectly balanced, has many specific laws that govern it. Laws that could have been different if the slightest change occured at the creation of our Universe (Big Bang or use your theory of everything). For all we know, at the end of our Universe (emptiness), another big bang can occur INSTANTLY also taking an eternity or an infinite amount of time to occur, all at the same "time" (kind of like the theories of a black hole). Our current laws and dimensions do not apply in that state. You are right, it is an opinion and I should have explained it more clearly. In the end of it all, theories are opinions, they are just more widely accepted because it makes sense.
DaveC426913
#135
Feb21-12, 11:12 AM
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Quote Quote by phasl001 View Post
In the end of it all, theories are opinions, they are just more widely accepted because it makes sense.
This is not true. Theories are not opinions, they are models that match the facts we observe. And how widely accepted they are is directly proportional to how well they match the facts.
phasl001
#136
Feb21-12, 11:29 AM
P: 4
Quote Quote by DaveC426913 View Post
This is not true. Theories are not opinions, they are models that match the facts we observe. And how widely accepted they are is directly proportional to how well they match the facts.
Yet a theory remains unproven even if it has facts to back it up, therefor it is a highly scientific opinion, because anyone might think otherwise. For example, global warming, many believe that it is cause by increased carbon dioxide levels in the atmosphere. It is fact that carbon dioxide levels have risen and it is also fact that the earth is warmer than it really is. Regardless of the theory, it remains unproven and only a matter of opinion on what exactly is warming the earth. Sorry to go off topic, but I believe you are wrong. Which is my opinion :)

-Phil
DaveC426913
#137
Feb21-12, 11:39 AM
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Quote Quote by phasl001 View Post
Yet a theory remains unproven even if it has facts to back it up,
Theories are never proven. That is not the purpose of a theory.


Quote Quote by phasl001 View Post
therefor it is a highly scientific opinion, because anyone might think otherwise.
For example, global warming, many believe that it is cause by increased carbon dioxide levels in the atmosphere. It is fact that carbon dioxide levels have risen and it is also fact that the earth is warmer than it really is. Regardless of the theory, it remains unproven and only a matter of opinion on what exactly is warming the earth.
Yes. There are competing theories. Do not confuse that with opinions. This is a a separate topic. If you wish to understand scientific theory, feel free to open a new thread about it.
mathal
#138
Feb21-12, 01:49 PM
P: 71
Just a guess.

To the degree that gravity between particles has a diminishing effect on their inertial motion WRT each other, regions of space far from all receding galaxies will contain molecules of hydrogen which will separate from each other. Eventually each will be entirely alone in it's own observable universe. But even then each molecule will have virtual particles to interact with. There will still be time.

mathal
Spourk
#139
Feb21-12, 05:41 PM
P: 52
My first response to the OP was, "When you die, does the universe dissappear?"

The answers are just as philosophically confusing.

What I am getting from this thread, in short, do things still happen? If you were to pop into that universe, would you start to get really bored? That would be an indication that time still exists, BUT, without your boredom and you, there would be no one to measure it, so the question is kind of moot in the end.

Everything we see now indicates that time is going to pass with or without you, the entire crux is, "can it be measured, and if it can't, does it matter?".
petm1
#140
Feb27-12, 01:22 PM
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The simple answer is matter and it's associated energy, of which we are all a part, are what we count as time. The space we "see" is the difference between the emission and reception of a photon upon reception in the present or just another duration.
phinds
#141
Feb27-12, 01:37 PM
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Quote Quote by petm1 View Post
The simple answer is matter and it's associated energy, of which we are all a part, are what we count as time. The space we "see" is the difference between the emission and reception of a photon upon reception in the present or just another duration.
Uh .... ?
Grimstone
#142
Feb27-12, 10:06 PM
P: 69
Quote Quote by petm1 View Post
The simple answer is matter and it's associated energy, of which we are all a part, are what we count as time. The space we "see" is the difference between the emission and reception of a photon upon reception in the present or just another duration.
i iz stu-pid. wut yu say?
petm1
#143
Feb28-12, 10:39 AM
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If you believe in a single photon then the end of a photon's life or the end of a photons duration as a photon is what we see as space. Space/time is measured one photon at a time isn't it.
phinds
#144
Feb28-12, 12:08 PM
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Quote Quote by petm1 View Post
If you believe in a single photon then the end of a photon's life or the end of a photons duration as a photon is what we see as space. Space/time is measured one photon at a time isn't it.
Sounds like nonsense to me.


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