According to relativity theory, all massless particles must travel at the speed of light. Although the photon is the only massless particle of which we have a good mathematical understanding, it is commonly believed that gravitational waves (which have not yet been detected, but are predicted to exist by general relativity) are composed of other massless particles known as gravitons, which also travel at the speed of light.
No particle with mass can travel at the speed of light, because it would require an infinite amount of kinetic energy to do so.
You are correct in that a photon can act like a wave or a particle depending on how it is observed. This indicates that a photon is neither a classical wave or a classical particle, but a more complex quantum object incorporating features of both.
In order for an electron to spiral into the nucleus it would have to continuously radiate energy, but energy can only be radiated in quanta and there is no allowed quantum of energy that would permit the electron to jump to thenucleus.
A subatomic particle has wave properties and the lowest non-destructively interfering orbit is the ground state where a complete wavelength of a 3 dimensional standing wave can be accommodated.
The UP would cause an electron in a smaller orbit than the ground state to have a higher velocity and therefore higher energy which means the orbit would be unstable.
None of this is of really correct but it may serve to give some idea of what is going on.
Sorry about the whole ‘orbit’ business. I knew an electron could not be said to ‘orbit’ a nucleus and I meant to add that disclaimer to my post but I forgot. Of course now that I see everyone elses post I can give myself a :smack: for not using the term ‘orbital’.
As to the probability cloud I am a bit confused. I understand that an electron does not circle an atom as a planet does a sun but I thought there were still defined energy levels (which equate to distance from the nucleus) at which an electron could establish itself. The way you explain the probability cloud it sounds as if the electron can be at any distance and merely prefers certain orbitals. However, in order to release a photon it has to do so in quanta and you can’t have a ‘fractional’ quanta. If the electron can presumably be anywhere then doesn’t that suppose fractional energy levels? (NOTE: I use the term ‘fractional’ loosely here since I do not know the proper terminaology but hopefully the sense of what I’m asking gets across.)
Whack-a-Mole, for a given energy level of an electron orbiting a nucleous, there is a probability distribuition describing the location of the electron. Diferent energy levels (which are, as you said, quantized) produce distribuitions of a different nature. An electron in the lowest orbital of an atom could be found twenty-miles away from the atom. Its not very likely, really, but someone who knew how (not me) could calculate the probabilty for you.
Actualy, I don’t even know if the figures needed for the “twenty mile” calcualation are known to enough precision to make the result mean much, but its just an example.
Whack-a-mole, The orbitals are not always arranged such that higher energy equates to further from the nucleus. For higher energy orbitals, on average the electron density is greatest further from the nucleus.
At risk of confusing major kong, orbitals can be all over the shop. Hybrid orbitals come in all sort of shapes. Again, the orbital describes a certain probability of finding an electron and they all have different energy levels. I suppose you could say an electron (as a particle) can move from position closer to the nucleus to a position further away. But it is better to think of the electron/orbital as a probability function, rather than a particle.
How long does it take an electron to fall to a lower energy level and release a photon? Obviously, the photon can’t be “produced” until all the extra energy of the electron has been expelled.
To use a gravitational analogy, when you raise a book up, you give it potential energy. As the book falls to the ground, the potential energy is converted into kinetic energy. When the book hits the ground, the kinetic energy is than transfered into sound energy (ie, THUD!). Now, it takes time for the book to fall, and during the fall, the energy is stored between KE and PE. So how does this work in the case of an electron?
(perhaps I’ll start a separate thread for this very question)
whackamole if you think in probability function then you dont have to worry about fractional energy levels. I suppose it comes down to this - think of electrons/orbitals as probability distributions, not particles.
antechinus: I know the Bohr orbit model is incorrect, and I’m familiar with the shell theory (though on a chemistry basis, not a physics basis); so my confusion isn’t from that fact. But even in the shell model (aka, probability cloud model) I still don’t see how the energy transfer can be instant. At best, it would be at the speed of light. And how can there not be an intermediate step? That would be like PE being converted instantly and directly into sound.
Don’t think of the electron as a particle. Think of a standing wave. A guitar string can vibrate with a node at each end and an anti-node in the middle; this is the fundamental. The second harmonic has a node at each end and a third node in the middle with two anti-nodes. It can vibrate at its fundamental frequency or the second-harmonic – There is no in between. The wave that is the electron is more complex than this, but the basic idea is the same.
It’s more like light, shich also behaves like both at times. In fact the Young double slit experiment that shows the wavelike nature of light can be performed with electrons too.
In an orbital, an electron behaves like a wave. Other times it behaves like a particle. So is an electron a wave or a particle? It is neither. Sometimes it behaves like one, sometimes the other. The above is true for photons, quarks, and well, everything. The square of the height of the wave is the probability the the particle will be observed at a particular location. The reason we don’t observe the wave-like behavior of ordinary day-to-day objects is that for larger objects, the wave is very narrow compared to the size of the object. With photons and electrons, the wave is wider than the particle, so the wave-like effects are more apparent.
Does a wave need a medium to travel through? What does an electron, quark, photon travel through?
So an electron is like a photon is that is behaves as either a wave or a particle depending on how it is observed? Does it matter that an electron has rest mass?
The problem with modern physics is that language quickly breaks down when trying to conceptualize these sorts of things. In order to begin to grasp the ideas without extensive mathematics (which is the only language that can definitively describe what we are talking about), you’ll need to accept certain ideas as being basic:
Every object, whether a subatomic particle or not, has a wave function which can be observed under the right circumstances. We could theoretically perform the double-slit experiment with Buicks if we had enough energy and time at our disposal. This doesn’t mean it is a wave, only that it appears to behave like one.
Particles don’t really travel through space in straight lines. Their wave function states that they have a particular probability of being at a given location in space at a given time. For instance, a photon simultaneously exists in every point in the universe, with the probability of it being detected at a given location being dependant on its wave function. The probability is much higher along a straight line from its source to its target, thus we normally will detect it there.
Hi Op…no. The waves which compose particles aren’t actual, physical waves, like sound waves or ocean waves. It’s convenient to think of them that way at times, but understand that it’s only a concept. They don’t need a medium to travel through, like ocean waves need water.
Yes, this is all very confusing at first, but only because our human languages are inequipped to handle this level of weirdness.
All “particles” can be regarded as “waves”, and vice versa. Depending on the situation, though, one interpretation will usually be more useful than the other. When you’ve got electrons in a cathode ray, like the beam which is spraying onto the back side of your TV screen, it’s easier to treat them as particles. But when they’re “orbiting” the nucleus of an atom, it’s easier to treat them as waves. And the mass of the particle (or lack thereof) is relevant to calculating things like the wavelength, but it doesn’t change the fact that there is a wavelength.
I would just like to say that this is one of the best, most informative threads I’ve ever seen on this board. And that’s saying a whole lot. For one thing, it has sure helped me understand the connections and overlap between the old orbital model and the “new” quantum cloud model of atoms.
One quick terminology question from the English major: When you speak of an object’s “wave function”, what you mean is that it is possible to describe a particle mathmatically with something like a sine or cosine wave, right?
Dang it, me and Major Kong are going to understand photons if it harelips everybody on Bear Creek!