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Messages - Guthers
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« on: 09/10/2012 15:08:40 »
I've thought a bit more about what an observer standing on the shell would actually see.
Let's say you have a flashlight which can emit a beam of light while rotating at a constant rate. The emitted beam falls on a distant spherical shell upon which the observer is situated.
From the flashlight's initial orientation (A) the beam hits a point on the shell (P) (arbitrarily) 10 light minutes away from the observer, and after 10 seconds the flashlight has rotated to its final orientation (B) so it is pointing directly at the observer (O). After hitting the shell some of the light is scattered so that the observer can see it. It can be seen that the point of illumination on the shell might be considered to be travelling at considerably more than the speed of light, 10 light minutes in 10 seconds (although changing position would be more accurate).
When the flashlight reaches B, the light emitted from A is already 10 seconds away on its journey, and this difference is maintained until the light reaches the shell a time t seconds later, so it is obvious that while the light from B reaches O after t seconds, light from A, travelling the path APO by scattering, takes t + 600 seconds. In fact it can be seen that all light which reaches O after being scattered off the shell will not arrive there until after light seen directly from B.
What O will see then, is a flash directly from the flashlight, then a bright spot on the surface of the shell receding from O, until it appears to disappear at P, 590 seconds later, representing the time at which the flashlight was switched on.
Incidentally, if O has a powerful enough telescope she could observe the flashlight start to rotate 10 seconds before seeing the flash of light from B.
Physics, Astronomy & Cosmology / Re: Why is the speed of light in a vacuum 300 million metres per second?« on: 08/10/2012 18:19:47 »
Sure, but irrespective of what units we apply to it, light still has a maximum speed of a certain value. Why is it that value, 300 million metres per second?
I think this is the same as asking why the speed of light is finite at all, since any numerical value we assign to it is purely arbitrary, depending on our perception of whatever time is. Other than that I like AI42's answer, that it can't go any faster because there's no fuel left to push it.
« on: 08/10/2012 18:08:14 »
I think you've said it yourself - "no material thing is moving faster than light". Your inference depends on the 'image' of the light on the shell being a physical object when it is nothing of the sort. The only reality of that image is that it is a product of your brain's interpretation of photons hitting your retina having bounced back from the shell.
The only things that are moving, apart from you and your flashlight, are those photons, which are moving at the speed of light in the local medium.
Imagine an analogy of a rotating cannon firing a steady stream of small bearings, representing the photons emerging from the flashlight. You can now watch successive bearings striking the shell, at a certain distance apart depending on the distance of the shell and speed of the bearings. Now if the experiment were set up just right, the interval between successive hits could be made shorter than the travel time of an individual bearing from one hit to the next would be, analogous to the 'image' in your scenario moving faster than light. This would obviously be impossible for a single bearing. However you can see that this is explained by there being more than one bearing accounting for this phenomenon.
The image is then generated by the bearings rebounding into your retina and triggering the generation of reality in your concious mind.
« on: 30/07/2012 14:18:33 »
There is no way any Earth organisms would be able to survive and live in Martian conditions, however modified. They are just too different. The main reason for not wanting to contaminate Mars, or anywhere else - they crashed the Galileo probe into Jupiter rather than risk accidental contamination of Europa, is to prevent false positive results if it looks as if some kind of indigenous life is found.
« on: 18/07/2012 13:38:40 »
The question asked was "Could we introduce life on Mars in order to 'terraform' it?", to which I think the obvious answer is no.
Assuming this would be Earth life, it would have evolved to adapt perfectly to conditions already existing here, specifically on Earth. While the existence of living things on Earth has changed the face of the planet, they would have had to be able to thrive in the initial conditions, however even the most extreme of extremophiles would struggle to even survive on the Martian surface today.
'Terraforming' seems to me to be more an engineering problem, following which you might have conditions suitable for Earth life to take hold.
And then of course what would be the point? Unless there is a chance of humans being able to survive there in the future outside environmental domes would there be any?
« on: 18/06/2012 22:42:39 »
my point is light is not like a ball that you throw upwards, then it slows down and falls back to the ground. It always travels at the speed of light. Are we suggesting that when a photon leaves a body with sufficient gravity it travels upwards for a bit, and then slows down and falls back to the body? Cause that's what it means when an object is under the escape velocity.
Correct, the light doesn't slow down at all, which is a common misconception. However, if you watch from a distance it might appear to.
The light gets infinitely red-shifted by the gravitational field, and therefore has no energy left by the time it gets to the event horizon.
General relativity, bloody hell!
There aren't any gaps in the periodic table, but in theory you could have more and more elements at the top end, in extreme conditions and perhaps for very short times.
And a neutron star, by definition, doesn't have any protons as they have all been converted to neutrons, so can't be considered an atomic nucleus. The atomic number is the number of protons in the nucleus.
« on: 01/06/2012 15:37:51 »
To answer the question, you are right. All the Apollo missions went to completely different locations and they didn't see the footprints left by the previous missions.
« on: 01/06/2012 15:34:25 »
Not forgetting that some birds (parrots?) can live to 100 years or more. Also I seem to remember hearing lobsters can survive well into retirement age.
On a couple of other points above, I don't think brain cells ever get replaced. Once these cells die they are gone for ever. Stories of people who sustain brain injuries gradually recovering lost abilities are due to other undamaged parts of the brain adapting to perform new functions.
And then the question of whether future long distance astronauts (taikonauts?) would still be human, well are you looking for a definition of "human" which depends on the mental or the physical? The body is just a machine after all, and being human encompasses a very wide range of body shapes already. Even if our travellers evolve an extra arm or a second heart, they'd still be our descendants. If their brains evolve abilities which meant they look on us much as we would think of our smaller primate or even fishy ancestors then that might be a difficult question to answer. In the end, if we eventually meet aliens with whom we (they?) can communicate and are on the same wavelength, who cares what we would actually call ourselves?
« on: 28/05/2012 23:20:48 »
Didn't somebody try doing this years ago with a flask of elements and passing a spark through them? Obtained some organic compounds but not life as I recall. Obviously missing the 'key' ingredient.
I think that's right. Any change in measured speed is due to the observer, not intrinsic.
Well, for a lot of people, religion is a source of comfort, hope, solace, ....
But the things in religion which bring comfort, such as companionship or a specific goal in life, can just as easily be found without the actual belief in god and without having to organise the way society works around this, whereas we would all still be in caves without science.
I don't expect you to understand the equation,
I think he meant who is referred to by the "you" in your post, not who you are...
Anyway, I imagine the OP is completely confused by now, so to sum up, would it be fair to say that gravity has no effect on the speed of light per se, but that looking from a distance, from a differently accelerating frame of reference or different gravitation field, you (anyone) would measure it as being slower?
Science is the attempt to describe the physical world by observation, measurement, and the construction of consistent models which both agree with those observations and make predictions which can be verified by future observations.
It does, however, depend on the gravittional potential Phi. See derivtion at http://home.comcast.net/~peter.m.brown/gr/c_in_gfield.htm Einstein first proved this in 1907. It was also experimentally proven.
I am quite good with maths, but the meaning of all that is a bit beyond me. Is it saying that as you approach the black hole the local speed of light slows, first to walking pace, then finally zero at the event horizon? Because that goes against all that I remember from studying this.
Here's another link that explains it more clearly.
Although it does say:
So in the presence of gravity the speed of light becomes relative (variable depending on the reference frame of the observer). This does not mean that photons accelerate or decelerate. This is just gravity causing clocks to run slower and rulers to shrink.
So not completely unconfusing :-\
Thanks for the reply. I'm not so good with maths.
No. The speed of light in a vacuum is a universal constant, regardless of frequency, and does not change. The frequency might be red-shifted and the pathway might appear to be bent, but light does not get slowed or speeded up. Every observer will still measure the speed as c, no matter what frame of reference they are in.
The difference in time dilation between the Earths surface and a few hundred miles above the surface is minute but it is enough for the surface of the Earth to accelerate at 1g. Scaling that up to the size of a galaxy it must become very significant and should not be ignored.
Nonsense. Don't even try to explain what you think you mean by this, I will just avoid your posts in future.
That time contraction does not lead to time passing faster (from the reference frame of a distant observer).
The latter. If time contraction at the periphery is say 0.01% (and I have no idea whether that is the right figure, probably nowhere near) and at the centre is 100 times this because the density is also 100x, then time dilation at the centre would be 1%. Hence time at the centre would run at about 99% that of the periphery.
Just because time dilation is 100 times greater does not necessarily mean time runs 100 times slower. It might, but not necessarily and probably not in the case of the Milky Way, whose density is very low anyway.
Continuation of reply # 2 of this post.
That doesn't follow. Time dilation might be 100 times greater, but that wouldn't mean time itself is running 100 times faster.
« on: 30/04/2012 18:12:11 »
This idea was put forward in The Cosmic Ecosystem, by Alan Johnston, published 1980.
From memory it seems like Fabio & Lesage's (and Bamboozled's) idea, but it is a long time since I read it. I would offer to sell you mine but there are loads on Amazon at 1p.
« on: 30/04/2012 13:36:06 »
« on: 30/04/2012 13:10:37 »
This is one of those subjects where, as a layman, I am finding it difficult to accept what science is claiming.
I feel somebody has to try to address this, and even though I'm no logician I'll try.
First of all, that is your interpretation of what you think scientists and cosmologists are saying, and might not represent their own actual reasoning.
The classical circular argument goes:
"We believe god exists".
"Why do you believe that?".
"It is inconceivable for so many people to believe god exists if he doesn't, therefore he must".
(This was actually the basis of a BBC Radio 4 Lent Talk by John Lennox: http://www.rzim.eu/john-lennoxs-lent-talk-for-radio-4, and he's a maths professor at Oxford. I kid you not. And the BBC is allowed to broadcast this tripe completely uncontested, sheesh :( )
In other words a widely held belief in the existence of something is used as the only evidence for its own existence. The only other source might be the bible, upon which the belief is based in the first place, and so is neither independent of the argument, nor verifiable or authoritative.
So, unless you consider the observations leading to the inference in your first statement to be no more reliable than say, the bible stories, there already exists evidence in the form of observations which have been independently confirmed, that 'something' (dark energy) exists.
Now, your final 'Query-Statement', purporting to show a circular argument, breaks down, because there is authoritative evidence for dark energy (or at least its effects), whatever it turns out to be, and not just the mere statement of its existence.
Your 'Conclusion' also implies a further step in reasoning, when all scientists have in fact done is given the "something" a name, "dark energy", without actually speculating or stating exactly what it might be. Scientists don't just expect you to believe anything, they are actively out there trying to find out exactly what it is.
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