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The Rebel

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  1. Quite a lot of posts to get through, but here goes. 5614: It doesn't quite work like that, a photon has to hit the receptors in your eye which triggers an electrical impulse to your brain which is how you see.... the key point being that the photon has to go into your eye for you to see it. Ok so the model of a photon was possibly taken out of line there, in that light is not evident until it interacts with something (like the eye). Try this one, there was a thing I read in a QED book once that talked about how light is reflected through glass. It mentioned how light was reflected off the front and rear surfaces differently depending on the thickness of the material, some kind of percentage or something. It made you think if light were particles how would each photon know whether to bounce of the front surface without knowing the thickness of the material fist. I concluded it has to be that energy fields are involved and NOT that light is a stream of particles that change as and when they come into contact with the surface. Swansont: EM energy is quantized, and that's what we call a photon. You can also view it as a vibrational mode of the EM spectrum. What's the difference between the model and reality, if the model explains how reality behaves? So then what is a photon a particle?, a unit of energy?, a wave? The problem is the number of models we have. Each sit perfectly within their context but in abstract form I’m struggling to decide what a photon is, how its created, what the interaction is between emitting and receiving, i.e. by particle movement, by energy waves, etc. Nevermore: Light is a notion produced by the human brain. Without an eye, there is no light. Only photons. I disagree. Something is there, as Syntax252 says. Whether its a cluster of particles or an energy field. The eye is just an instrument to measure the light. It’s like saying there is no voltage on a power supply until you put your fingers in it. Cadmus: I do not think that it is extermely useful to consider light as a stream of particles It is useful, but it has flaws, especially in abstract. 5614: I prefer to think of light, or EM radiation as particles travelling in a wave. So (I've said this before) but just as a dolphin swims jumping in/out of water, so a dolphin (particle) jumping up and down (a wave). Are you saying light consists of both a carrier wave AND a particle. That a photon rides a wave until it hits something? That’s an interesting concept, I’d have to consider. Johnny5: The very fact that this discussion is even taking place, proves conclusively that physics needs a better photon model. One that can be derived out of context, and then have the equations applied to it to put it back in to explain all related sciences involving light. 5614: Just because someone doesn't understand does not mean that the thing they are trying to understand is no good. In their individual forms the models of the photon are very good, and helpful for their application. It is the combination of these and defining how what light is itself that is causing the problems. Technologist: Light has a dual nature. It can show characteristics of both a wave and a particle. Experiments on reflection, refraction, and diffraction clearly show that light displays wave like properties similar to waves of water or sound. On the other hand light shows characteristics of a particle. Assuming that the space between earth and the sun lacks enough material to transmit a wave, then how would light reach us if it wasn’t a particle? The photoelectric effect is evidence of the particle nature of light. All these are examples of how I find it difficult to imagine what a photon is. All the concepts that involve light like curving around a stellar mass, photoelectric effect, reflection, diffraction, absorption, constancy, mass-energy relationship, why doesn’t it drag when in motion, nature around black holes, how its created (e.g. light bulbs, transmitters), if photon is particle then what is it physically doing when it leaves a radio aerial?, its effects on particular chemicals (e.g. fading, sunburn, microwaving), polarisation, what the ether is and how it travels, why we can’t see it unless we are in direct view, reactions in different material thicknesses, etc, etc. I’m trying to understand what light is to provide a commonality across all of these, and not simply in example of photoelectric effect consider light as a particle, in reflection light is a wave, and have so models for the same thing just try to explain a particular concept.
  2. Anyone know where I can't get information on adhesives. I'm particularly after comparisons on Araldite, Loctite, RTV and Dymax. The web just takes me to sales and promotions. I want to know things like cure times, applications, strengths, durability, temperature limits, etc, etc. Thanks
  3. Seems like a simple question, cos we can see it? I'm not sure what sort of answers I'm gonna get, "cos it does, stupid", "cos einstein says so" or a link to another thread. My problem is in accepting light as a stream of particles (photons) that "travel" from one place to another. My preception is that as an energy change takes place, like fusion in the sun, and electrons get excited, it produces an EM field as oppose to creating a photon travelling away from the source. This EM field effects other surrounding matter, a bit like an iron filing is affected by a magnet. An example would be a cars headlights. From the side we can't see the "beam" of light (unless it is scattered in our direction by particles in the air), it merely hits the ground and the matter in ground reacts to it, upon which we see this "excitement" by receptors in our eyes, being stimulated by the new EM wave from the ground. If light were made of photons then wouldn't we see the beam from the side?, you can't say only one side of the photon is visible (the "front"). I guess my question is do photons actually exist or are they just theoretical models of whats happening. Some may say well certain experiments have detected a photon, but then anything that is a measuring a system, affects the system. The measuring instrument is merely in the EM field, and being affected, it isn't necessary picking up a "photon". Thanks.
  4. What is the objective of this counting experiment????
  5. I should imagine that the particles constructing the lid of the box would have to close the box at a speed greater than c. Otherwise the photon would escape before you had a chance of closing the box and trapping the light.
  6. You've almost got it except for the C bit. nCr is just a notation not a product, the C standards for combinations. You'll probably find nCr on a decent calculator next to nPr (permutations). If you do try entering 4 => nCr => 3 => ANS. You should get the answer 4. To evaluate the co-efficient nCr you use the formula given above. If you don't like using nCr, you can use Pascals triangle. Have a look at this => http://www.davidscudder.com/pascal/binomial.html
  7. Ok forget the assumptions bit, show me the way to a scientist that isn't making it up as they go along, but is in agreement to the theories science has produced and has accepted as true. For example, although we could all come up with different ways deciding what 1kg is, the only effective way is by comparing to the accepted international prototype of the kilogram. Do we have these baselines in physics or is what we have purely conjecture and the "truth" is what the majority agree with. I.e. the majority of people believe light is constant and have various ways of proving it over the minority, therefore it must be constant.
  8. You can usually prize off the key itself leaving the push button. A quick spray with electrical solvent, rub down and replacing the key should do the trick.
  9. Would be interesting to see a mathematical side to it though, thus proving dc/dt = 0. Although I can't help thinking this is already hidden in Maxwells' equations somewhere.
  10. Looking some stuff up on binomial expansion should reveal some ways it is used. It basically considers expanding the brackets into its individual terms: i.e. ... [math](a+b)^3 = (a+b)(a+b)(a+b) = a^3 + 3a^2b + 3ab^2 + b^3[/math] To remember how its done, you realise that the number of terms will be a more than the power. I.e. in the example above, a power of 3 gives 4 terms. The formula for each term when expanding [math](a+b)^n[/math] is [math]nCr * a^{n-r} * b^r[/math]. Where r is the term in the series (starting from 0). [math]nCr = \frac{n!}{r!*(n-r)!}[/math] Applying this above to [math](a+b)^3[/math], to find the 2nd term its, [math]3C1 * a^{3-1} * b^1=3a^2b[/math] Note the powers of a and b in each term always add up to n
  11. 5614, The interaction thing. What I'm getting at is we don't sense something until we interact with it. When the receptors in our eyes are stimulated, its from sensing the disturbance we are "looking" at. Light is what describes the way in which the disturbance travels to our eyes. Its hard to explain. It's a bit like electricity in a way, electricity itself does not exist its just what we call the interaction between disturbances in the electroncs . . . Anyway, definition of mass. I mean't rest mass, or more basically matter. I was trying to quote the orignal post which queried that mass could not be accelerated to speeds of c. I have a bit of a problem understanding space-time, may need to do some more research. You say space-time is bent but then what is space, is it the particles within space? whenever I try to understnad it in forms of a bowling ball on a sheet bending the sheet such as the ball bearings fall it, I think well that's because gravity is drawing the bearings down against the sheet. If photons have no rest mass, then they would not be "roll" towards the black hole. What's wrong with the idea that EM energies in the black hole matter are causing it instead?
  12. Matt if you can come up with a better explanation, be my guest.
  13. WOW!!! I'm away at the weekends but what a thread to come back to, very good reading. Just the sort of thing I'm trying to get into and understand. In my opinion, a photon is not really a particule but a packet of energy that forms a communication between two "talking" particles. For example a reaction in the sun causes electrons to react in such a way that is resonant with the receptors in our eye. Just like electrons vibrating in an aerial are resonant with a tuned radio circuit. With light there maybe interceptors along the way, such as when the energy is absorbed into particles in the sky, and consequently "new" energy sent on to our eyes. I don't think light actually exists per say, its just an energetic interaction. This leads me to appreciate the idea of photons not having mass, except in abstract form. With the sail thing, I think the high energy in the laser causes the electron configuration to take the equivalent of an electric shock. To the original question photons travel at c therefore don't have mass. No problem with that, the only thing that bothers me is where the value of C come from, i.e. why is it 300000000ms-1 all the time. A question that could be asked of all constants. And why are photons effected by black holes despite not having mass. This I believe to be the distortion of the EM energy between the "communicating" particles. I fail to consider matter without the presence of some of electromagenetic energy in the particles that make a black hole. And I think its these property of the black hole that distorts the energy path like a magnet distorts the tv screen. Please fault find my opinions, I'd really like to get to the bottom of this,
  14. This is one of the frustrating things I am finding with trying to understand the derivations of science through text books. One book happily provides a proof that [math]E=mc^2[/math], whilst a little research actually says no, [math]E^2=m^2c^4+p^2c^4[/math] How am I supposed to know what is right and wrong???
  15. The problem comes from the way the repeating is used and the assumptions made. I know a few people detest the use of infinity but sorry, its the only way to explain it. Imagine the number 0.99999999.... The rule of multiplying by 10 is to shift the decimal. 9.99999999..... But lets pretend infinity is a finite number, after multiplying by 10, the number at the right end of 9.9999999... is unknown. e.g. 0.999999 .... 999| (where | denotes the end of the number) 10 x 0.999999 .... 999| = 09.99999 .... 99x| x is actually unknown or undefined as it comes from outside the original number, we just take it as 9 because of the repeating factor. if we then introduce this into the 10X-X = 9X formula we'd get: 09.99999 .... 99x| - 0.999999 ....999| =09.00000 .... (x-9)| therefore 9X = 9 .... (x-9)| => X = 1 .... (x-9)/9| Because the difference is at the "end" of the repeating number, it is insignificant in size (infact by assuming x is 9, it equates to zero) but none the less shows that .99999 does not equal 1.
  16. If the gas characteristic is 2080J/(kg K), then 200g must contain 416J / K. Then you can use pV = kT
  17. The Rebel

    Momentum

    Do we consider the passenger to be isolated from the car, in which case (assuming the car comes to a dead stop) the passenger will leave at the speed before the collison (100km/h]. Because in essence the car and the passenger are different elements only related by what speed they were travelling. The difficulty comes in including components such as the seatbelt, the structure of the passenger, and the behaviour of the crumple or bounce of the collision.
  18. Maybe the full bladder isn't so far off. I was thinking that perhaps the erection is a means of the body stopping you from urinating whilst you're asleep. This could also explain why infants tend to be more prone to "wetting the bed".
  19. Imagine a car that is being accelerated from rest. The engine is doing work which is directly providing an increase in KE. So' date=' Change in KE = W = F*d = mad One of the velocity formulas that relates to changes in velocity is: v[sup']2[/sup] = u2 + 2ad, which reduces to v2 = 2ad as u = zero. therefore Change in KE = mv2 / 2
  20. Infinity can't be defined, therefore 1 divided by infinity can't be defined. It's just assumed as a limiting factor to be zero, when used in calculus for example.
  21. You need to be a bit more definitive in what type of tracking device you're after. There is GPS tracking that positions you on the earth, but more locally there are magnetic trackers or more recently optcial trackers. The magnetic trackers work on a transmitter that sends electrical pulses using three coils positioned in x, y and z. A receiver detects the strengths of these pulses at certain times to determine where the receiver is with respect to the transmitter. More modern trackers are using optics whereby the moving object is covered in emitting optical devices which are in a known 3D matrix, received by optical sensors.
  22. I don't believe in warping time (thats for another thread), but given that QM identifies that time and length can be dilated, wouldn't the further dimensions revolve around dilation, a reference frame, and frame of reference for the 4D event.
  23. An update from something I found in one of physics books, under the heading of thermal conduction in solids: "Since electrons are the carriers in electrical conduction, it is considered that electrons transport energy through metals. Thus on heating a metal bar the free electrons gain thermal energy and distribute this energy by collision with the fixed positive metal ions in the solid lattice. Poor conductors ... have no free electrons. The transport of thermal energy ... is mainly due to waves. They are produced by lattive vibrations due to the thermal motion of the atoms. The waves are scattered by atoms ... and so distribute thermal energy to the solid. The energy and momentum of the waves can also be considered carried by particles (p.877)" <<p.877 talks about wave-particle duality "These particles are called phonons. Like the waves they represent, they travel with the speed of sound"
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