How can a lowly photon travel from 13.8 billion light years and reach out telescopes without "dying" in space, since there are atoms and molecules in every cubic meter of space?
Hi Bill. Thank you for the answer. If that is the case, are there different energies that photons possess from the time they were released, that enables them to travel the vast distances across the universe?There are very few atoms in interstellar space, almost all of them are ionized hydrogen, thus only protons floating around. No photon can be absorbed by a free proton.
The ability of a photon to travel across the universe is independent of its energy, all photons travel in a vacuum at the speed of light. It is possible for two photons to join together to produce an electron and a positron but their energies must total more than 1.02 MeV and it must occur in the presence of a strong electric field such as a heavy atom such as uranium or lead in order to conserve momentum. It cannot occur in free space.
OK! Calm down. 🙂 I was thinking more in terms of the geometry than the intensity at the start of the transmission. Given the tiny radius of the source transmission the spread of each individual photon trajectory would be massive at 21 trillion meters distant, and given that the planets are grouped at a maximum of 10 trillion meters around the sun, a miss is a definite possibility.Not only would the signal not miss the Solar System, it would not miss a coffee cup.
This post is not meant to be contentious in any way, it merely illustrates a wish to try to understand the problem better. Just checked your figures and they seem to be approximately accurate. The volume of a football field is approx. 21333.7 cubic yards to the height of the goal posts. 21333.7 cubic yards translates to 1.63 x 10^10 cm ^3. There are approx. 2.7 x 10^19 air molecules in one cm^3 of air so a total of 2.7 x 10^19 x 1.63 x 10^10 = 4.4 x 10^29 molecules of air in the football field (approx..) If the dia of the speaker is 30 cm (1 ft) it will have an area of is 707 cm ^2 approx. This area will impact 707 x 2.7 x 10^19 = 1.9 x 10^22 air molecules. Now take a hypothetical shot gun shell containing 1.9 x 10^22 pellets (approx.) each pellet will be separated from every other pellet by 4.4 x 10^29 / 1.9 x 10^22 = 2.3 x 10^7 cm . (203 km!) Exclamation mark mine. For all I know these figures might be completely off but it does serve to demonstrate the difference between how a wave and a solid object travel.The air in a football stadium is comprised of something on the order of 10^30 molecules, each one which is shifted back and forth by a sound wave. Billions of them impact every eardrum, thus everyone hears the noise.
A shotgun shell might hold a couple of hundred pellets. By the time they reach the other side of the field they are each several feet apart, not every person will encounter one.
You cannot take the number of pellets in a stadium (4.4x10^29), divide that by the number of pellets touching a speaker cone (1.9x10^22) and get a distance (210km). You get a dimensionless number which is the number of pellets that got moved by each pellet moved by the speaker cone.
OK, just to put things in perspective the ray from a pocket laser would be about 13 Km across by the time it reached the moon! Although scientists have been trying to get a reflection back from mirrors placed on the moon, it is only now after 25 years of trying (2020) that they have managed to get a reflection back from a laser. This too is not from a reflector placed on the surface of the moon but from a reflector placed on the lunar orbiter. So¸ it is really a non sequitur to try to equate the manner in which a particle travels with the way in which a wave travels. There is a huge difference. Consider a grain sized particle For instance there about 10^19 molecules in a grain of sand, roughly the same number of molecules that a 30 cm dia speaker would interact with but you cannot expect that grain of sand to interact with all of the molecules in the air, it is not possible even though the number of molecules that the speaker interacts with and the molecules in the grain of sand are the same.Yes, photons are individual particles. As they travel outwards they get separated from each other. In the case of Voyager I, by the time the cloud of photons reaches the Earth, they are separated from each other by an average of about 2 inches. We are easily able to intercept enough of them to generate a signal in a radio receiver.
In any case you were quite right, I made the mistake of taking the number of molecules of separation as centimetres, the difference would be much less than a centimetre, maybe a thousandth of a centimetre. But, that doesn't mean I am wrong, read the previous post (#15).You cannot take the number of pellets in a stadium (4.4x10^29), divide that by the number of pellets touching a speaker cone (1.9x10^22) and get a distance (210km). You get a dimensionless number which is the number of pellets that got moved by each pellet moved by the speaker cone.
I am only quoting what I have read at multiple sources:The first laser ranging experiments of the Moon were done in 1962 by US scientists at MIT and again by Soviet scientists in the Crimea. In both cases they received photons bounced off the Moon's surface.
Just getting to this. If Cat wants a difficult question for Bill, maybe we should ask him to explain how individual photons make diffraction patterns when going one-at-a- time through a pair of parallel slits. That still seems to stump everybody.
Ok, but this is like the dumb thermos joke. Hot liquid is kept hot, and cold liquid is kept cold. "How does it know?"It is not just individual photons that create a diffraction pattern when going through parallel slits, but particles do it as well. This is due to the wave nature of all particles. The smaller the particle the bigger its wave function and the more pronounced the diffraction pattern. This has been verified by experiment. It is due simply to Heisenberg uncertainty priciple, you cannot simultaneously determine exact position and velocity of anything. A particle does not have a definite size or location and thus acts as a wave at small dimensions. This is all counter to our macro experience but none the less true at microscopic dimensions.