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    Quantum immortality

    You miss the point LnGrrrR. There are no 900 year old people in 'my' universe because the conditions that ensure my survival are extremely unlikely to do so for someone else for such a length of time. So it goes, any person to have ever existed (or, indeed, any person that could have possibly...
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    Quantum immortality

    RVBuckeye I see what you mean but, without any predictions about what should change, it can't really be held up as evidence that the idea is wrong. Sherlock You are very dismissive. I am not necessarily a believer in the MWI but the idea provides a certain symmetry don't you think? I...
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    Quantum immortality

    I'm not certain if, strictly, this should be in the general discussion forum but the idea is based on quantum ideas so I have put it here. If I am mistaken, please, move it. I stumbled upon this idea when I was reading through lots of different interrelated articles on Wikipedia (it can be...
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    Richard Feynman Lectures on Light

    Wonderful. I have revision that I have to do now so I don't know when I'll watch them all but I definitely will.
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    Phase velocity, Group velocity

    Thank you, I shall have a look but I actually think that I have a good enough understanding now having read a few relevant sections in the Feynman Lectures (sorry, this is what I should have done first).
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    Phase velocity, Group velocity

    Would someone be kind enough to please give physical meanings to these two terms? I have never fully understood their meaning and difference (although I know how to express them mathematically). If, say, I have a Gaussian-shaped signal in the frequency domain that I am sending through a...
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    When a free proton captures a free electron

    Or (for completeness) several photons whose sum is the ionization energy.
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    Greatest physicist of all time?

    Exactly, this is why it is very hard to see past Newton as the greatest physicist ever.
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    Twice as hot?

    Surely, it is only technically acceptable to say it if the temperatures are measured on an absolute scale (such as the Kelvin scale)?
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    Basic concept in special relativity

    Nicely put rbj. At first, I thought that it doesn't cover the situation where the light source is stationary and the observer is moving but, from the observers point of view, the source is moving not him and, so, to him, your argument should still apply. If it didn't, the laws of physics would...
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    QED vs Point Charge of the Electron

    Excuse my ignorance but how so?
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    About EM waves

    Whilst that isn't how I understand it, it could be one correct way to understand the situation. My understanding is that virtual photons propogate and cause the electric field and real photons are emitted as EM radiation when charges accelerate. You seem to be saying the inverse of this. An...
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    Basic concept in special relativity

    Thank you for all replies. I will have to work on my communication skills regarding science. I often feel, when I return to special relativity having not considered it for awhile, that I have to partially learn the subject all over again (that, in a sense, being part of the reason that I...
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    Basic concept in special relativity

    I was asked (on another non physics site) how an observer can measure the speed of light to be the same as someone who is moving away/ towards the light source. I know that it is a fairly simple idea but I couldn't find the words to answer comprehensively. Here is what I wrote: In...
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    Okay, clear this up for me

    I believe that dark matter is thought to have exotic properties such as possibly only interacting via the gravitational force (hence, why it has only been 'detected' through it's gravitational influence). If that is the case, I suppose that the dark matter 'on' your table would pass through the...
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    Most persistent myths.

    May I ask you to explain why everything (in the physical domain) cannot be reduced to pure physics?
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    Most persistent myths.

    At what point did this thread turn into: "state some things that in which you personally don't believe but cannot prove either way"? God (whether He exists or not) should surely not be mentioned on this thread.
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    A question about wavefunction

    It seems to me that you are asking why <x|p>=exp{ipx/h} but surely you must have this derivation in your notes? BTW, the above equation isn't actually quite right (needs a factor in order to normalize it) and, in my notes anyway, the 'h' is actually an 'h-bar'. As regards your other...
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    Russian girl with x-ray eyes

    Hmm, x ray vision? How is that even supposed to work? I mean, what is the source of these x rays that she can see?
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    Here's a toughy about pulleys and friction

    I don't follow this at all. How can the question say: "The coefficient of static friction between the table and the block..." when a table has not been previously mentioned? Is there a diagram?
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    Certainty and Classical Physics

    I remember reading a point made by Feynman that, in a classical world, even the most minute of errors in measurement of one particle in a system would result in indeterminism eventually because of error propogation.
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    Mathematical derivation for gravity

    I thought that it was too simple a reply. As far as I know, Newton came up with that by finding that the force should be proportional to the mass of each body and inversely proportional to the distance between them squared. I believe that this was a prediction rather than a result of...
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    Mathematical derivation for gravity

    Combining Newton's 2nd law of motion with Newton's law of gravitational attraction gives your result: F=\frac{GMm}{r^{2}} F=ma The acceleration, a, is labelled g.
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    Cosmic particles result in lightning

    I read about this in New Scientist magazine. It postulated that cosmic rays caused lightning. Unfortunately, you cannot access the internet page to view the whole article without subscription (
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    Guess what guys

    You can see Mars comfortably with the naked eye. Mars isn't too far from the Pleiades at the moment if that helps.
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    Pseudo force

    I suspect that it would be reasonable to state that work was done by a pseudo force (centrifugal force due to gravity) in making the Earth bulge at the centre during its formation.
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    Magnets and gravity

    Do you mean to ask if it is possible to have a magnet orbit another magnet as the Moon orbits the Earth? If so, I don't think that it is possible without magnetic monopoles.
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    Guess what guys

    I, myself, have recently been watching the sky in awe, I have rediscovered a love of looking at the night sky that I developed as a child. It was the thrill of seeing a particularly bright point in the sky and suspecting that it wasn't a star before finding out that it was Mars that did it for...
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    Black holes and galaxies

    I once had the thought that black holes are self contained universes where three new spatial dimensions (and presumably a new time dimension too) were created from bending the existing dimensions through an unseeable right angle. In a sense, these would be new universes. I seriously doubt the...
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    Is it really gravity?

    This has been an odd thread to read. Could a centripetal force really cause our weight on the surface of the Earth? Absolutely, however, the source of the centripetal force is gravity! Replacing gravity with gravity is a somewhat novel idea. I hope that the originator of the thread has...