Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Ron Hughes on 04/05/2011 17:47:47
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This was also posted here http://www.thenakedscientists.com/forum/index.php?topic=39022.msg354554#msg354554
A clock just outside the event horizon of a black hole will appear to be almost stopped to an observer far away. That same clock will appear to run faster on Earth, faster on the moon and faster in empty space. Those four locations will have an average rate which suggests the Universe has an average rate based on the matter energy density of the Universe. In space I have a device that will emit a beam of light which I call device A. Three hundred thousand kilometers away I have a detector which I call device B. Some distance away I have a clock which is entangled with device A and B such that when A emits the beam my clock starts and when device B detects the beam my clock stops. I trigger device A to fire and my clock shows a time of one second determining the speed of light to have it's current value. I now move my clock to the edge of the event horizon of a black hole and trigger device A again. If my logic is correct don't I measure c to be almost infinite?
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This was also posted here http://www.thenakedscientists.com/forum/index.php?topic=39022.msg354554#msg354554
A clock just outside the event horizon of a black hole will appear to be almost stopped to an observer far away. That same clock will appear to run faster on Earth, faster on the moon and faster in empty space. Those four locations will have an average rate which suggests the Universe has an average rate based on the matter energy density of the Universe. In space I have a device that will emit a beam of light which I call device A. Three hundred thousand kilometers away I have a detector which I call device B. Some distance away I have a clock which is entangled with device A and B such that when A emits the beam my clock starts and when device B detects the beam my clock stops. I trigger device A to fire and my clock shows a time of one second determining the speed of light to have it's current value. I now move my clock to the edge of the event horizon of a black hole and trigger device A again. If my logic is correct don't I measure c to be almost infinite?
Entanglement doesn't work like that; your setup would require the transfer of information at superluminal speed, no matter how many times people say "quantum entanglement" usable information like this is not transferred instantaneously. And as soon as info is not transferred instantaneously then you have a problem with simultaneity, when this problem is solved using lorentz, SR and GR then you will again get the speed of light as c
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If there is a way to communicate information instantaneously, it can only be instantaneous in one preferred reference frame. A good guess is that the preferred reference frame, if it exists, is stationary relative to the CMB. Our view of the CMB is blueshifted in the direction of Virgo, indicating relative velocity of our solar system at about 627 km/s toward Virgo. This translates to a relativistic gamma of about 1.0000022.
If the reference frame of the CMB is a preferred reference frame, and instantaneous communication is possible in that frame, then there is a universal time for all locations at the same gravitational potential. I am less sure about whether that universal time is applicable at different gravitational potentials. I might have to think about that one for a few more years before answering.
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:)
And now for mine definition. Time as such has only one rate macroscopically, having a 'direction' temporally. That rate you can find anywhere in the universe just by checking your heartbeats to your wristwatch. You will find your time to be the exact same, no matter from where you measure it. Just as the speed of light.
That it is so has indeed to do with radiation as I see it now. If you instead measure someone else's clock, at the event horizon of a black hole for example, you will find it to be 'still' relative yours. That is also defined as being different 'frames of reference' and is explained by the relativity of simultaneity. (http://en.wikipedia.org/wiki/Relativity_of_simultaneity).
A simple way to view it is to consider that if light is the best 'clock' available, and if time and space is one indivisible in Einsteins definitions. Then the geometry of the space, combined with our best 'clock' which we agree that light (radiation) is also being a constant, will produce a 'time dilation' when motion or mass gets involved. And as you can define Earths gravity as a constant acceleration at one G, we can find a (rather weird:) equivalence to motion there too.
To me your time never change, but your room time geometry may. And comparing frames of reference doesn't mean that you change the intrinsic 'clock' you have, the time measured for your life is the same wherever you go. The thing differing is that intrinsic clock relative other frames of reference, like the universe at large, if you're waiting at the Event Horizon.
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If time is variable across the universe due to it's connection with energy and mass then a Universal Constant for time would only exist where gravity is the same.
I see this as lots of bubbles all different sizes and only the bubbles of the same size have the same time reference, Universally that is.
This might mean that not only do we observe light from the past but time itself exists in a layer of infinite pasts!
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Wow, a thought experiment that engenders absolutely no logical response.
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A constant is thought to be something that is valid from, and in, all frames of reference as I understands it Airthumbs. It becomes a 'magical number' sort of, thought of as something that seems to define SpaceTime. And it also depends on your theories how and what you might find to be a 'constant'. So if you want to look at the universe as 'different time densities' then those can be no constants.
But in a way I've also thought about if there is a way to connect different frames of reference to each other by using the 'SpaceTime' they will see when 'the same'. Like Rindler observers, having the exact same 'speed', being at rest relative each other but at different locations. You might argue that what they see is the 'same' in form of radiation and the universe. But all such ideas will go out from one 'coherent universe' where we all exist the same. But we don't, we all see the universe different, although it's not noticeable until at relativistic speeds that we do.
The thing connecting what you see to what I see is the light 'propagating' between us. And at relativistic speeds where you define the distance to a star, per your Lorentz contraction, to be one light year away, whilst I being at rest relative your origin (Earth), finds you to be ten light year away but your 'clock' to 'tick' ten times slower both are correct.
For you the time never changed, but your 'distance' did with your acceleration. For me tha 'distance' stays the same but your 'time' doesn't. and that's what I mean with there is one universe for each one of us, with light signals being what give us the impression of us all being in the 'exact same one', time dilation and Lorentz contraction notwithstanding.
In Einsteins universe there is one truth. The constant invariant speed of light in a vacuum.
The rest is open for negotiation as I see it :)
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Wow, a thought experiment that engenders absolutely no logical response.
Come up with logical thought experiment that doesn't require us to ignore agreed laws of nature and you might get a response that you like more. Gedenken that require suspension of preconceptions are fine, those that require suspension of physical laws are not. Also I would be interested for you to point out the logical flaws in any of the above responses - they might range from boring dogmatism (mine) to slightly off the wall (anon) but what makes them unsound?
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Ron, what was illogical about Imatfaal's initial response?
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I still like my time bubbles as they exist in a Multiverse! POP
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Bill S, He is dodging the problem. Go back to when the Universe is four million years old. A clock then would run very slow compared to today. From a clock's frame of reference then c would be much faster.
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Bill S, He is dodging the problem. Go back to when the Universe is four million years old. A clock then would run very slow compared to today. From a clock's frame of reference then c would be much faster.
Ron,
I suggest that you review the definitions of meter, second and speed of light. The speed of light (in m/s) can't change while it is defined as a constant ratio of distance/time (in m/s). How are you defining the speed of light? You obviously are not using the official definition.
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A light source that starts at T = 0 and travels 300,000 km in one second as measured by a clock is how we measure c. Light would not slow in the early Universe but the clock you use to measure it with would. Therefore when you make your measurement the light beam would travel a much greater distance giving c a higher value.
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A light source that starts at T = 0 and travels 300,000 km in one second as measured by a clock is how we measure c. Light would not slow in the early Universe but the clock you use to measure it with would. Therefore when you make your measurement the light beam would travel a much greater distance giving c a higher value.
No it wouldn't [:D]
As far as I know, the speed of light is/was constant, so the distance light travels in one second will always equal about 300,000 km.
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Bill S, He is dodging the problem. Go back to when the Universe is four million years old. A clock then would run very slow compared to today. From a clock's frame of reference then c would be much faster.
Not dodging the question at all - just saying it is unrealistic. Your question is the equivalent of starting a question "as 2+2=5 then we can...."
You are missing the basic point of SR that with a fixed and finite speed of light simultaneity is often illusory and measurement must be boosted/contracted/altered to ensure that they all fit in the same calculation. Your two points A and B are 300,000,000 m apart - how are you telling, from where your clock is (which can be at A or at B but not at both), that light has transited that gap? Once you remove your faster than light communication the communication of one or both events has to be passed back to you at a maximum of light speed. Once you have done this and taken into account the other factors that relative velocity or an accelerating reference frame will have you will come out with c equalling c.
If you remain unconvinced bear in mind that the existence, homogeneity, and redshift of the CBR were predicted many years before it was observed. these predictions relied intimately on the speed/wavelength of light and our theories of the ancient universe. If the speed of light was so different - what else changed, by exactly the right amount, to leave us predicting the right amount of redshift?
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Ron, light is, as I see it, unchanging. That you will find some other clock to go slower than yours is SpaceTime adapting to this fact. If you look at it the way Einstein described it SpaceTime is one thing, not several. The dimensions all adapt to one constant, and that's lights constant unvarying speed.
We live in a universe defined by light.
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There seems to be one underlying theme with this debate, that "c" is invariant. However, I have a problem envisioning the reality of length contraction due to motion. I prefer to accept that TIME really does change since this has been proven experimentally. Length contraction has never been proved to be a reality. This being the case, we cannot then hold velocity constant between two moving frames and deduce length contraction because we are afraid to challenge the limit of "c". What we must do is to allow velocity to exceed "c" (but only within the moving frame) due to time dilation and Lorentz. This does not affect the RELATIVE limit of "c" in all other frames, but does explain WHY "c" is the limit. ie, as you approach "c", your speed approaches instantaneous speed. (Just like a light beam).
Cab anyone educate me as to why this approach might be wrong, or could it, in fact be right ?
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There seems to be one underlying theme with this debate, that "c" is invariant. However, I have a problem envisioning the reality of length contraction due to motion. I prefer to accept that TIME really does change since this has been proven experimentally. Length contraction has never been proved to be a reality. This being the case, we cannot then hold velocity constant between two moving frames and deduce length contraction because we are afraid to challenge the limit of "c". What we must do is to allow velocity to exceed "c" (but only within the moving frame) due to time dilation and Lorentz. This does not affect the RELATIVE limit of "c" in all other frames, but does explain WHY "c" is the limit. ie, as you approach "c", your speed approaches instantaneous speed. (Just like a light beam).
Cab anyone educate me as to why this approach might be wrong, or could it, in fact be right ?
I'll take a shot at this, and JP can sort me out where I'm wrong [:)]
Fundamentally, science says that light always propagates through space at c. (It might help to imagine that space is actually "something", but mind how you go with that idea.)
If you observe that light is propagating through space at something other than c, either your clock, your measuring stick, or both, need to be recalibrated.
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There's a list of tests of sepecial relativity here:
http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html
There is no direct test of length contraction, since it's incredibly hard to measure. However, as the site points out, the magnetic force due to an electrically neutral, current carrying wire on a moving charged particle is explained by length contraction.
There are a lot of tests of other aspects of special relativity, which are reproducible. Any new theory that actually differs from SR needs to explain these experimental results.
Finally, I find that a lot of debates on the finer points of relativity come down to semantics. SR is a very nonintuitive theory (to me, at least), and it requires that all people discussing it agree very precisely on what they mean by time intervals, lengths, speeds, etc. I've seen many debates on SR come down to the fact that the two posters agreed on the physics, but were using slightly different definitions of terms.
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Take a look here Time Dilation - An Experiment With Mu-Mesons. (http://www.scivee.tv/node/2415) Then look at this Muon Experiment. (comparing frames of reference) (http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/muon.html)