Welcome to
Science a GoGo's
Discussion Forums
Please keep your postings on-topic or they will be moved to a galaxy far, far away.
Your use of this forum indicates your agreement to our terms of use.
So that we remain spam-free, please note that all posts by new users are moderated.


The Forums
General Science Talk        Not-Quite-Science        Climate Change Discussion        Physics Forum        Science Fiction

Who's Online Now
0 members (), 139 guests, and 0 robots.
Key: Admin, Global Mod, Mod
Latest Posts
Top Posters(30 Days)
Previous Thread
Next Thread
Print Thread
Page 3 of 7 1 2 3 4 5 6 7
Joined: Mar 2010
Posts: 1,100
K
Megastar
Offline
Megastar
K
Joined: Mar 2010
Posts: 1,100
Originally Posted By: Bill S.

Could it not be argued that on the roundabout we know we are moving because we have experienced acceleration, whereas the world around us has not.


Sorry but it's exactly how I thought things worked too. Tho there is that possibility the roundabout might be enclosed in a massive spinning sphere, so we'd feel acceleration even tho we're not rotating relative to the distant stars. But it seems like more of a special theoretical case rather than what actually happens.

.
Joined: Aug 2010
Posts: 3,570
B
Megastar
Offline
Megastar
B
Joined: Aug 2010
Posts: 3,570
I am still not happy about the acceleration argument. Consider this thought experiment. A spacecraft passes the Earth at 60% of c. On the craft is a pair of twins. As the craft passes the Earth, one twin heads for Earth in a shuttle, and lands. The craft continues. Later, it executes a wide turn with no change of speed. Obviously, the manoeuvre causes a velocity change, but this is kept to a minimum, and is probably no greater than the positive and negative acceleration experienced by the other twin. After a journey of 10 light years the craft passes Earth, as it does so, time dilation tells us that the twin on the space craft is younger than the one on Earth, but how can this be attributed to acceleration?


There never was nothing.
Joined: Feb 2007
Posts: 1,840
R
Megastar
Offline
Megastar
R
Joined: Feb 2007
Posts: 1,840
Originally Posted By: kallog
Originally Posted By: Bill S.

Could it not be argued that on the roundabout we know we are moving because we have experienced acceleration, whereas the world around us has not.


Sorry but it's exactly how I thought things worked too. Tho there is that possibility the roundabout might be enclosed in a massive spinning sphere, so we'd feel acceleration even tho we're not rotating relative to the distant stars. But it seems like more of a special theoretical case rather than what actually happens.

Seems to me that either one accepts or does not accept that there is no single reference point from which all motion is measured - i.e., that all motion is relative. If one takes rotational velocity to be an exception, then one has the task of explaining why. But hey, I reserve the right to be wrong twice before breakfast smile


"Time is what prevents everything from happening at once" - John Wheeler
Joined: Mar 2010
Posts: 1,100
K
Megastar
Offline
Megastar
K
Joined: Mar 2010
Posts: 1,100
I don't think we can have the choice for constant velocity motion. Unless we imagine something for which there's no evidence.

The way I see acceleration is your velocity changes from what it was before. So everybody knows it's changed. Not everybody may agree on how fast it was before, but at least they agree how much it changed by.

So it doesn't require any special reference frame. If you like, one usable frame would be the intertial frame of the previous state of the object before its speed changed.

Joined: Aug 2010
Posts: 3,570
B
Megastar
Offline
Megastar
B
Joined: Aug 2010
Posts: 3,570
I am not questioning the relativity of motion, nor doubting that acceleration can occur without a change of speed. Neither response has actually addressed the fundamental questions in my previous post. I.e. Is the more travelled twin younger that the one who hopped off onto the Earth? If so, why? Both have experienced acceleration. The major difference between them is a period of travel at a speed that has remained constant relative to the Earth.


There never was nothing.
Joined: Feb 2007
Posts: 1,840
R
Megastar
Offline
Megastar
R
Joined: Feb 2007
Posts: 1,840
Needless to say I have an opinion, Bill, but it would be unreliable in the absence of the maths to back it up. It might be difficult to find a suitably qualified person who can give you a definitive answer, but you could try Ask a Scientist:

http://www.newton.dep.anl.gov/aas.htm


"Time is what prevents everything from happening at once" - John Wheeler
Joined: Jun 2008
Posts: 415
S
Senior Member
Offline
Senior Member
S
Joined: Jun 2008
Posts: 415
The mystery between Time and Quantum of light.
===.
When quantum of light moves with constant speed c=1
the Time is constantly frozen,
Questions.
How does constantly frozen Time broke and variable time appear?
In which Reference frame the frozen Time exist?
In which Reference frame the variable time exist?
What is interaction between these two systems?
#
According to SRT time depends on speed.
According to GRT time depends on mass.
And I ask maybe mystical , maybe scientific question:
Does quantum of light have influence on the time?
===.
Israel Socratus.

Joined: Aug 2010
Posts: 3,570
B
Megastar
Offline
Megastar
B
Joined: Aug 2010
Posts: 3,570
Well done Socratus! You have brought us back, at least close to the point where Gan set things in motion.
With regard to your questions, I would suggest trying to think of time as a static entity, through which we are moving. In that way, time does not have to change from being “frozen” to being variable, any more than space has to change when we start to move about.
Only in the frame of reference of an observer does time appear to change. True, relativity tells us that an observer in motion relative to something else can with equal validity consider herself to be moving, or the “something else” to be moving, but in the case where the “something else” is time that may make no more sense than Einstein’s alleged question: “Does Oxford stop at this train?”
A photon travelling through a vacuum must, as you say, be stationary in time. However, if it passes, for example, through the Earth’s atmosphere it slows slightly, thereby experiencing some passage through time in its F of R, but time remains unchanged.
I would argue that time does not depend on either speed or mass. Only an observer’s perception of time is altered by these things, and then only in his F or R.
Here’s a question though. The photon in a vacuum must be at every point on its journey at the same time. If it is going from A to B, it must be at B at the same time that it leaves A. Now suppose that between A and B it passes through the Earth’s atmosphere which slows it down slightly, so it experiences a passage through time, thus delaying its arrival at B. Now we have a situation in which the photon is at A and B, in its F of R, at the same time; but it also arrives at B shortly after leaving A, also in its own F of R. What is more, this situation is not improved if we reason that we cannot know anything about what the photon does on its way between A and B. How can it arrive in one place at two different times in its own F of R?


There never was nothing.
Joined: Aug 2010
Posts: 3,570
B
Megastar
Offline
Megastar
B
Joined: Aug 2010
Posts: 3,570
Sorry, I seem to have duplicated my last post; must be something to do with my lack of technical know-how.


There never was nothing.
Joined: Mar 2010
Posts: 1,100
K
Megastar
Offline
Megastar
K
Joined: Mar 2010
Posts: 1,100
Originally Posted By: Bill S.
Sorry, I seem to have duplicated my last post; must be something to do with my lack of technical know-how.


Haha. When I do that I prefer to blame the lack of human know-how of the people who developed the software. They should have made sure you can't accidentally do that.

Anyway, back to the twins. The situation isn't symmetric. The one who continued on still had to accelerate to turn around. If he did it slowly then he experienced a lower acceleration, but spent a longer time doing it. That means you can't necessarily make the effect arbitrarily small. If he could turn around with a small acceleration for a short time, then it would be reasonable to say that's as good as no acceleration at all.

Joined: Mar 2010
Posts: 1,100
K
Megastar
Offline
Megastar
K
Joined: Mar 2010
Posts: 1,100
Originally Posted By: Bill S.

going from A to B, it must be at B at the same time that it leaves A.

Now suppose that between A and B it passes through the Earth’s atmosphere which slows it down slightly, so it


If it slows down on the way then it can no longer be at A and B at the same time.

Or are you saying, when it starts out it 'thinks' it's already at B because it doesn't see the Earth in the way. Then somebody puts Earth in its path, so suddenly it has to not be at B anymore.

Joined: Aug 2010
Posts: 3,570
B
Megastar
Offline
Megastar
B
Joined: Aug 2010
Posts: 3,570
Kallog. I was not looking for a situation that could be equated to "no acceleration at all", but in this scenario both twins have experienced acceleration. I don't have the maths to work out which would have the greater effect, so let's try a different tack. If the travelling twin keeps going in a straight line at constant speed, at the point at which he is 10ly from Earth, is he younger than the other twin? There may be no way he could know that for sure, but the age difference should be there, unless we are saying that the age difference exists only if it can be directly observed.

As far as the photon is concerned, I am not saying that "when it starts out it 'thinks' it's already at B"; I am saying that it is at A and B, in its own F of R, in a sort of infinite "present". There is no need for someone to put the Earth in the way. The photon would have to be aware of the presence of the Earth at the outset, and would have no time in which to be aware. I think I am beginning to answer my own question, so I shall stop rabbiting, and do some thinking.


There never was nothing.
Joined: Mar 2010
Posts: 1,100
K
Megastar
Offline
Megastar
K
Joined: Mar 2010
Posts: 1,100
Originally Posted By: Bill S.

travelling twin keeps going in a straight line at constant speed, at the point at which he is 10ly from Earth, is he younger than the other twin? There may be no way he could know that for sure, but the age difference should be there, unless we are saying that the age difference exists only if it can be directly observed.


Hmm. If the travelling one stopped when he got to 10ly, then we could know for sure because they'd both be in the same reference frame. One way is to have clocks strewn about the universe, all stationary in the Earth's reference frame, then no matter how far away you are, you can tell the time. Not that I have an answer, but it'd be nice to figure one out.

If the travelling one didn't stop, then I'm pretty sure the people on Earth, looking through their telescopes and accounting for light travel time, would see him as being younger than the twin on Earth. But here the situation may well be symmetrical, with the travelling one also seeing the Earthy one being younger.

Joined: Jan 2007
Posts: 2,311
Megastar
Offline
Megastar
Joined: Jan 2007
Posts: 2,311
Originally Posted By: Bill S.
Kallog....As far as the photon is concerned, I am not saying that "when it starts out it 'thinks' it's already at B"; I am saying that it is at A and B, in its own F of R, in a sort of infinite "present"....

"a sort of infinite present"? Pardon the intrusion. Sound's like what I have mind when, in the Not-Quite-Science section, I use the acronym 'G0D'

Earlier you wrote
Originally Posted By: Bill S.
Well done Socratus! You have brought us back, at least close to the point where Gan set things in motion.

With regard to your questions, I would suggest trying to think of time as a static entity, through which we are moving....
I agree. Interestingly Paul, in Acts 17:22-28, expresses the same concept of God--as the one in whom we live, move and exist.

http://www.biblegateway.com/passage/?search=Acts%2017:22-28&version=NLT

I prefer using the acronym. It helps me avoid thinking anthropomorphically--that is, thinking of a god in a human-like and limited form:

http://www.tnellen.com/cybereng/lit_terms/anthropomorphism.html
===========================

Last edited by Revlgking; 09/04/10 04:10 PM.

G~O~D--Now & ForeverIS:Nature, Nurture & PNEUMA-ture, Thanks to Warren Farr&ME AT www.unitheist.org
Joined: Aug 2010
Posts: 3,570
B
Megastar
Offline
Megastar
B
Joined: Aug 2010
Posts: 3,570
Revlgking: There is no intrusion - welcome to the thread. Have you read Julian Barbour's "The End of Time", Oxford 2000? He has an interesting take on the idea of static time.


There never was nothing.
Joined: Aug 2010
Posts: 3,570
B
Megastar
Offline
Megastar
B
Joined: Aug 2010
Posts: 3,570
After lots of thinking, and numerous cups of tea (which undoubtedly betrays my location as UK), I have come up with some thoughts I would like to share; i.e. have kicked around.

A photon is a quantum object. I suggest the use of Nick Herbert’s “quon” for a quantum object. (This definition found its way into Wikipedia yesterday.)

Quons are able to be in more than one place at a time, as long as they are not being observed. As far as I am aware, we have no evidence to indicate that the restriction to a single place, which we observe from our F of R, also applies in the F of R of the quon. In its own F of R it may still be everywhere at once. It may exist in infinity (=eternity).

Eternity is not an infinite expanse of time; in fact, it does not involve time, the two concepts are, incompatible. The concept of eternity as being in any way “temporal” arises from our limited ability to comprehend the nature of infinity. Like “Flatlanders” who cannot even imagine a third spatial dimension, we try to examine infinity using only our four dimensions of spacetime. Thus we find ourselves constantly falling back on temporal analogies and terminology, which are, at best, only of limited value, and, at worst, are downright unhelpful.

John Wheeler said that “Time is nature's way to keep everything from happening all at once”. This may sound like a flippant comment, but it is in fact quite a profound observation. We might say that eternity is the absence of time, and that in eternity everything must happen at once. However, even that statement is misleading: in order for something to happen there must be some passage of time. In eternity, everything just is.

Whatever one can do with mathematical infinities, it seems inescapable that any physical infinity must be immutable. The corollary of this is extremely important. An infinite cosmos cannot be multiplied nor divided. It can have nothing added to it, because there is nothing outside it that could be added. It can have nothing taken away, because to take something away would either make it less than infinite, or it would mean that there was something other than the all-embracing infinity, which would constitute a contradiction in terms.

If we were able to divide infinity, for example, by two, what would we be left with? One possibility seems to be that we would have two halves of infinity. Each half would be less than infinite, thus it would be measurable. Measure this quantity and multiply it by two and we have a measure of infinity, which is nonsense. The second possibility must be that each “half” somehow becomes infinite. Mathematically this seems reasonable; after all we can multiply or divide zero by any number we choose, and the outcome will be zero. Perhaps we also could do this, mathematically, with infinity, (Cantor almost certainly did), but practically there is the complication that anything that is truly infinity must contain everything; there cannot be two infinities, because each would have to contain the other.

This apparently intrinsic indivisibility of infinity leads one to wonder if any “part” of infinity can be distinct from any other “part”. Is it in any way meaningful to talk of parts of infinity? If it is not, and if our Universe is “part” of this infinite cosmos, then we seem to have a problem. However, the problem may not be as difficult to solve as it at first appears. Consider the following possibility. The cosmos is infinite; therefore every part of the cosmos is the whole cosmos. Everything, including our apparently finite Universe, is infinite. The birth of the Universe and perhaps its ultimate death exist together in infinity, along with all the things that seem to us to “happen” between those two points. It is all there, in eternity, in an all-embracing now. We perceive spatial differences, and the passage through time, because our minds need to make sense of the partial image to which we are restricted.

Consider events A, B and C. In linear time these might occur, one after the other, in that order. In eternity, though, they would all be present together. There could not have been a point in eternity when, for example, A had happened, but not B or C. The whole of eternity must contain A, B and C, in their entirety, for all eternity.

Just when you thought I had wandered infinitely far from the point, this brings us back to our photon travelling from A to B, via the Earth’s atmosphere. In our F of R there is a passage through time involved, but in the Photon’s F of R it is at A and B, and in the Earth’s atmosphere all at the same infinite point.


There never was nothing.
Joined: Jan 2007
Posts: 2,311
Megastar
Offline
Megastar
Joined: Jan 2007
Posts: 2,311
Bill S. IMO, this sounds like the "mind" that I am IN, when I think: GOD.

BTW, tell us how you feel about theology.


G~O~D--Now & ForeverIS:Nature, Nurture & PNEUMA-ture, Thanks to Warren Farr&ME AT www.unitheist.org
Joined: Mar 2010
Posts: 1,100
K
Megastar
Offline
Megastar
K
Joined: Mar 2010
Posts: 1,100
Originally Posted By: Bill S.

immutable. The corollary of this is extremely important. An infinite cosmos cannot be multiplied nor divided. It


What do you mean by cosmos? It seems you distinguish it from the universe which you describe as finite. Do you mean something 'outside' the universe? I think that's more of a psychological desire. Still, even the universe might turn out to be infinite, so all your comments can apply to that too.


Quote:

anything that is truly infinity must contain everything; there cannot be two infinities, because each would have to contain the other.


There isn't that requirement. For example how many integers are there? Infinitely many. Now how many real numbers are there? Also infinity. But yet the infinite set of integers is only a proper subset of the apparently larger and more inclusive set of real numbers. Mathematicians call these "countable infinity" and "uncountable infinity". I guess there are other ways to classify different types of infinities too.



Quote:

there is a passage through time involved, but in the Photon’s F of R it is at A and B, and in the Earth’s atmosphere all at the same infinite point.


If it slows in the Earth's atmosphere then it's <c, so it experiences passage of time, so it's not at A and B simultaneously.

Joined: Aug 2010
Posts: 3,570
B
Megastar
Offline
Megastar
B
Joined: Aug 2010
Posts: 3,570
Originally Posted By: Kallog
What do you mean by cosmos?


Perhaps it would help if I outlined the way in which I use a few terms. It might be good if others, who use these terms differently posted their versions as well.



1. Universe: following John Gribbin, this is what started with the Big Bang. It is what we observe around us, and what I believe is finite.

2. universe: this could be any member of a multiverse, or any theoretical universe that might be under discussion.

3. cosmos: anything, including our Universe or a multiverse which may, or may not extend beyond that which we can observe, detect or definitely prove to exist. Personally, I believe that it is the cosmos, within this definition, that is infinite.

4. infinite: that which is all-embracing, boundless and eternal. Nothing that exists can be separate from infinity, nor can anything that is at any point finite become infinite. Our Universe may be unbounded; it may continue to expand for ever, but it will never become infinite.

5. eternal: because we are constrained to think in 4-D terms, we find it necessary to impute to infinity a temporal facet. This distinction exists only in our limited perception.

Quote:
how many integers are there? Infinitely many.


I wondered who would be the one to raise this argument.

Up until the early nineteenth century, mathematical existence was rather similar to physical existence. Both were considered to exist in the real world. The discovery of non-Euclidean geometries changed that view. Mathematical ‘existence’ came to mean only logical self-consistency and this did not require physical existence to complete it. If mathematicians could write down sets of non-contradictory axioms, and formulate rules for deducing true statements from them, then those statements were held to ‘exist’. If there can be such a profound difference between physical and mathematical “existence”, or “truth” then it seems reasonable to identify a similar difference between physical and mathematical infinities. The infinite series is entirely a mathematical entity.

Quote:
If it slows in the Earth's atmosphere then it's <c, so it experiences passage of time,


Let us not forget that even when light is travelling at "c" we, in our F of R perceive a passage through time. Can we be sure that the apparent reduction of the speed of light in the Earth's atmosphere is not also a feature of our limited perception? Why should there be any change, of any sort, in the F of R of the photon?


There never was nothing.
Joined: Jan 2007
Posts: 2,311
Megastar
Offline
Megastar
Joined: Jan 2007
Posts: 2,311
Bill S., I think it was Carl Sagan--the astronomer and great popularizer of science-- who said of the cosmos: "The cosmos is all that is or ever will be."
I write more about this at:
http://www.wondercafe.ca/discussion/religion-and-faith/hawking-outs-god-creation

Meanwhile, it is great to read interesting dialogue without the silly comments from people who lack the ability to debate without personal attacks.


G~O~D--Now & ForeverIS:Nature, Nurture & PNEUMA-ture, Thanks to Warren Farr&ME AT www.unitheist.org
Page 3 of 7 1 2 3 4 5 6 7

Link Copied to Clipboard
Newest Members
debbieevans, bkhj, jackk, Johnmattison, RacerGT
865 Registered Users
Sponsor

Science a GoGo's Home Page | Terms of Use | Privacy Policy | Contact UsokÂþ»­¾W
Features | News | Books | Physics | Space | Climate Change | Health | Technology | Natural World

Copyright © 1998 - 2016 Science a GoGo and its licensors. All rights reserved.

Powered by UBB.threads™ PHP Forum Software 7.7.5