A question on the speed of light

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A question on the speed of light

Postby ekzrated » Fri Feb 29, 2008 2:21 am UTC

As you all are painfully aware, I'm uneducated, and I use it as my excuse to ask anything that I can think of. SO, to the point of this thread.

Everything we know about the universe is all based on scientific theory. I've often been told that there is nothing faster than the speed of light. Is this because we haven't discovered anything that can travel faster, or is it because we're going on the same principles of the observable universe? I mean, if we look at the solar system and compare it to an atom, there's definitely similarities, and really speed and time wouldn't mean anything if we talk relativity. What makes us so sure that there is nothing capable of going faster? Would we even be able to recognize such a wave? Please discuss openly.
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Re: A question on the speed of light

Postby mrbaggins » Fri Feb 29, 2008 2:55 am UTC

The problem is that the definition of a particle (having any mass) and the formulas regarding the speed of light and movement rule each other out.

It is also worth noting that if you were travelling at just under the speed of light, and you shone a torch forward, that it still leaves you at the speed of light. IE: Nothing can reach the speed of light, because the speed of light is always C+Yourspeed.

(NB, just in case, C = speed of light)
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Re: A question on the speed of light

Postby Durandal » Fri Feb 29, 2008 3:00 am UTC

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Re: A question on the speed of light

Postby antonfire » Fri Feb 29, 2008 4:03 am UTC

It all stems from the assumption that the laws of physics, (including Maxwell's equations) don't depend on whether you're moving. In other words, if you're in a closed-off box, you have no idea whether it's moving in a straight line or just sitting there.

The theories based on this assumption, including bizarre time-dilation effects and the like, have been tested to pretty good precision.

Also, physicists accelerate small particles to damn near the speed of light on a regular basis. They give them energies such that, if you didn't take into account relativity, they'd be travelling at more than ten times the speed of light. They don't. Instead, they travel at something like 99% of the speed of light.

It's pretty well tested.


The thing is, along with the theory of relativity comes weird causal issues in frames of reference. If something travels faster than the speed of light in one frame of reference, then it actually goes "backwards in time" in another frame. So if you like relativity (and we do) and you like causality (and we do), you don't like things travelling faster than the speed of light.
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Re: A question on the speed of light

Postby Zanik221 » Fri Feb 29, 2008 5:27 am UTC

mrbaggins wrote:It is also worth noting that if you were travelling at just under the speed of light, and you shone a torch forward, that it still leaves you at the speed of light. IE: Nothing can reach the speed of light, because the speed of light is always C+Yourspeed.

The really crazy thing is that if there's an observer in front of you, that light you're projecting is approaching him at C, from his frame of reference, not just under 2C.

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Re: A question on the speed of light

Postby ThinkerEmeritus » Fri Feb 29, 2008 1:13 pm UTC

A hypothetical particle travelling faster than light is called a "tachyon." Given special relativity, they have some strange and basically unattractive properties. They can only travel faster than light, their energy goes down with increasing velocity, and their "rest mass" is imaginary. [This rest mass has nothing to do with their energy at v=0, since they can't travel at v=0.] At one time there were some candidate particle theories that necessarily contained tachyons, which was generally viewed as a black mark on the theory. There have been efforts to detect tachyons which didn't find anything. Googling on "tachyon" will produce a list of pages which among them no doubt have more than you ever wanted to know about faster-than-light particles.
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Re: A question on the speed of light

Postby rrwoods » Fri Feb 29, 2008 8:18 pm UTC

Here's something I never got:

So, say I'm traveling at C/2 towards a stationary observer. I emit a photon (or a whole bunch of photons) at the observer. From my frame of reference, the photons travel at C, and given that my frame of reference is moving at C/2, I see the photons strike the observer at time T. From the observer's frame of reference, the photons also travel at C, which would cause them to strike the observer at time 2T. This appears to be a contradiction.

What am I missing?
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Re: A question on the speed of light

Postby daydalus » Fri Feb 29, 2008 8:24 pm UTC

rrwoods wrote:Here's something I never got:

So, say I'm traveling at C/2 towards a stationary observer. I emit a photon (or a whole bunch of photons) at the observer. From my frame of reference, the photons travel at C, and given that my frame of reference is moving at C/2, I see the photons strike the observer at time T. From the observer's frame of reference, the photons also travel at C, which would cause them to strike the observer at time 2T. This appears to be a contradiction.

What am I missing?


Someone else can explain further, but this has to do with the time-distortion effects of traveling at speeds approaching C.

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Re: A question on the speed of light

Postby Owehn » Fri Feb 29, 2008 8:26 pm UTC

You're missing time dilation and length contraction. The two observers won't agree on either of the following measurements:
1: The amount of time it takes the photons to travel.
2: The distance the photons travel.
When you take both of these phenomena into account, everything works out to be consistent.
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Re: A question on the speed of light

Postby ekzrated » Fri Feb 29, 2008 8:59 pm UTC

I suppose part of the problem with finding something which surpasses the speed of light is knowing what to even look for.

I am always interested in scientific research and development, but I can't help but think that we have a long way to go. I thought time didn't exist, though.
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Re: A question on the speed of light

Postby Owehn » Fri Feb 29, 2008 9:08 pm UTC

O Magic 8-Ball, does time exist?
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Re: A question on the speed of light

Postby ekzrated » Fri Feb 29, 2008 11:39 pm UTC

I see what you did there. But if we're discussing things in terms of general relativity, what does it matter how fast light goes when you'er thinking in galaxy-sized proportions? Surely there's more to it than light.
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Re: A question on the speed of light

Postby Hit3k » Sat Mar 01, 2008 2:30 am UTC

Theres always darkness... That always seems to get there before light...
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Re: A question on the speed of light

Postby dosboot » Sat Mar 01, 2008 3:49 am UTC

I think we should be more careful talking about hypothetical objects moving faster than the speed of light. Mathematically the equations say they move backwards in time but if we do not know of any such particles would it really contradict any observations if they did not?

On a completely unrelated note, it is possible have something crudely analogous to moving faster than the speed of light. Imagine a long line of light bulbs which are sequentially turned on, with a t second delay between when consecutive bulbs. As t gets arbitrarily small, the speed at which the leading bulb appears to move is arbitrarily large. The only catch is that there is no way that this can send information faster than c. It would have to happen by chance, not as cause/effect chain reaction. But this light bulb will appear to move faster than c in every sense of the word. One can imagine a very long line of such bulbs in space. Watching them from a distance they will appear to out race a spaceship moving at .9c

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Re: A question on the speed of light

Postby ThinkerEmeritus » Sat Mar 01, 2008 4:36 pm UTC

dosboot wrote:I think we should be more careful talking about hypothetical objects moving faster than the speed of light. Mathematically the equations say they move backwards in time but if we do not know of any such particles would it really contradict any observations if they did not?


Antiparticles can be interpreted as the corresponding particles moving backwards in time. I don't think tachyons have to be interpreted that way. If they were, their antiparticles would move forward in time and you would be right back where you started from.

There may be causality problems with tachyons. I've forgotten what the situation is and whether or not the problems might be cured by reversing cause and effect, essentially reversing time.

Of course, tachyons have been looked for and not found.

dosboot wrote:On a completely unrelated note, it is possible have something crudely analogous to moving faster than the speed of light. Imagine a long line of light bulbs which are sequentially turned on, with a t second delay between when consecutive bulbs. As t gets arbitrarily small, the speed at which the leading bulb appears to move is arbitrarily large. The only catch is that there is no way that this can send information faster than c. It would have to happen by chance, not as cause/effect chain reaction. But this light bulb will appear to move faster than c in every sense of the word. One can imagine a very long line of such bulbs in space. Watching them from a distance they will appear to out race a spaceship moving at .9c


This is essentially the "lighthouse effect." If the bulb in a lighthouse rotates so fast that its linear speed is just below the speed of light, and the beam is seen against a fog bank a sufficient distance away, the spots made by the flashing beam seem to be moving along faster than the speed of light. As you say, no information is passing from one spot to the next one; all the information is coming from the lighthouse at an entirely acceptable speed.
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Re: A question on the speed of light

Postby SpitValve » Sat Mar 01, 2008 5:03 pm UTC

ekzrated wrote:I see what you did there. But if we're discussing things in terms of general relativity, what does it matter how fast light goes when you'er thinking in galaxy-sized proportions? Surely there's more to it than light.


I don't get what you mean. We see something 8 billion light years away, then we're seeing what it looked like 8 billion years ago. That's pretty important

ekzrated wrote: I mean, if we look at the solar system and compare it to an atom, there's definitely similarities,


Nope!

Similarities between an atom and the solar system:

1. Large massive object in the centre with a force inwards towards it
2. Small objects "orbiting" around that object

Differences:

1. Electrons can only occupy discrete energy levels, planets can orbit any way they want
2. Planets are attracted to other planets, electrons repulse other electrons (gravity is always attractive, electrostatic force is sometimes attractive and sometimes repulsive)
3. Electrons are best described by a wavefunction, where momentum and position can not be well-defined at the same time. A planet can have a definite momentum and a definite position
4. An electron is (as far as we know) indivisible, and has no real "size". Planets have lots of substructure, can be split apart, joined, exploded, they have clouds, mountains, seas, sand, people etc
5. Planets have moons and things
6. Large groups of star systems look like star clusters and galaxies. They never form a regular lattice structure like a crystal of atoms can form.

and so on. Basically: there is not really all that in common, and any philosophy based on "solar systems/galaxies might be atoms in another universe" is simply wrong.

and really speed and time wouldn't mean anything if we talk relativity.


Speed and time do have meaning in relativity. They follow quite definite laws. They're just not the same laws you're used to.

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Re: A question on the speed of light

Postby Pathway » Sun Mar 02, 2008 3:42 am UTC

dosboot wrote:I think we should be more careful talking about hypothetical objects moving faster than the speed of light. Mathematically the equations say they move backwards in time but if we do not know of any such particles would it really contradict any observations if they did not?

On a completely unrelated note, it is possible have something crudely analogous to moving faster than the speed of light. Imagine a long line of light bulbs which are sequentially turned on, with a t second delay between when consecutive bulbs. As t gets arbitrarily small, the speed at which the leading bulb appears to move is arbitrarily large. The only catch is that there is no way that this can send information faster than c. It would have to happen by chance, not as cause/effect chain reaction. But this light bulb will appear to move faster than c in every sense of the word. One can imagine a very long line of such bulbs in space. Watching them from a distance they will appear to out race a spaceship moving at .9c


It's an illusion of motion, though--not actual motion.

I remember doing a similar problem in physics last year where I had to show that you can get the result you just described by shining a laser at the moon from Earth, and flicking it around really fast. It turns out the spot of light can travel faster than c. But nothing is actually moving faster than light--the spot isn't composed of any physical objects.
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Re: A question on the speed of light

Postby Azrael001 » Sun Mar 02, 2008 4:27 am UTC

I don't think that the spot would move at faster than C. When you have a laser beam shoot out at something once you get a dot, it will take just as long for the dot to move as it did to get there in the first place.


Sort of like this (Laser goes this way <-----:
<--------------------------_____ All of this light will hit first,
oooooooooooooooooooooooooooooo----___ then this will
ooooooooooooooooooooooooooooooooooooooooooooooooooo---__ then this.
The stream would bend and the dot would not move as fast as C.

edit: there should be spaces in my laser diagram, curses. o's are now spaces
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Re: A question on the speed of light

Postby Owehn » Sun Mar 02, 2008 5:13 am UTC

If I have a laser pointing at a distant object and start to turn the laser, then yes, the spot will take as long to start moving as it took the light to get there. But the speed at which the spot moves (once it does) increases linearly with the distance to the object, so for a far enough object the spot will move faster than light.
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Re: A question on the speed of light

Postby Azrael001 » Sun Mar 02, 2008 5:30 am UTC

I see what you are saying. I'm sure that it is wrong for some reason, but now I can't disprove it. Something about gaps in the beam, I don't know, I'm tired. Tomorrow I may be more coherent.
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Re: A question on the speed of light

Postby EricH » Sun Mar 02, 2008 6:34 am UTC

Azrael001 wrote:I don't think that the spot would move at faster than C. When you have a laser beam shoot out at something once you get a dot, it will take just as long for the dot to move as it did to get there in the first place.


Sort of like this (Laser goes this way <-----:
<--------------------------_____ All of this light will hit first,
----___ then this will
---__ then this.
The stream would bend and the dot would not move as fast as C.


If your intuition tells you the dot will not move faster than C, then either you didn't understand the situation, you're using different definitions, or your intuition is wrong. Possibly more than one of the above.
The stream (if by that you mean the stream of photons emitted by your laser) will indeed bend, as the laser rotates. Let's try a ridiculously long thought experiment, to restate the situation (spoilered for space):
Spoiler:
Imagine you're at the center of a Dyson sphere, eight light-minutes in radius. (For your safety, we'll remove the star that would normally occupy this position.) You hold in your hand a multi-megawatt laser pointer, but it is otherwise dark, so you'll be able to see the dot it forms, when it hits the inner surface of the sphere. You turn it on, and see nothing. Complete darkness. You hold it still, and wait. Eight minutes later, the laser reaches the inner surface of the sphere, and illuminates a point. You still see nothing. After you've had the laser turned on for 16 minutes, at last you see a dot appear, right where your laser is pointing, because that's how long it takes for the light to get there and back again. Now that you can see the dot, you slowly turn the laser to the right. Over the course of a minute, you turn it all the way around in a circle, and end up pointing straight ahead, again. While you turned, the dot did not appear to move, because you're still looking at light that was produced when you were holding steady, waiting for the dot to appear. Fifteen minutes later (be glad it's a thought experiment, so you don't have to wait 15 minutes for results), as you sit, holding steady, you see the dot move to the right. Over the course of a minute, it goes all the way around you, and ends up straight ahead, once again. Now for analysis: The light always moved at speed c, directly from the center of the sphere to the inner surface, then directly back again. Any given photon made the round trip in exactly 16 minutes. Obviously, you and your laser pointer were not moving at anywhere near light speed, and the sphere didn't move at all. So there were no objects or particles that exceeded the speed of light, at any time, because that's all the pieces involved in this thought experiment. What did move quickly--faster than light--was the dot: that is, the illuminated point on the inside of the sphere, which appeared to move at 16*pi*c, since it traversed a circle 16*pi light minutes in circumference, in one minute.
But the dot isn't an object, and it can't carry information. It's not made of anything. You can see the dot race around the circle, but the photons are all moving directly out from the center, or directly back in, just as when the dot was stationary; not one photon is traveling a circular path, even a little bit. Ooh, here's an extension to the analogy, that might help: let's say your laser pointer is the laser sight on a machine gun. During the minute you turned, you fire continuously, all the way around the circle. Certainly, bullets are a lot slower than light, but in free space, they will get there eventually. In about six years, I think. So, one day, six years later, a bullet strikes the inner surface of the sphere. A couple of milliseconds later, another bullet strikes, hundreds of miles away. Two milliseconds later, a third bullet, hundreds of miles further on. The barrage continues, right around the interior of the sphere, and you can measure that the impact point, where the bullets are hitting, 'moves' at 16*pi*c. But obviously the bullets aren't going anywhere near that fast. If you could see all the bullets at once, from above the plane they're all in, you'd see that the bullet stream is curved, in a spiral, even though every single bullet is moving in a straight line.
When we're talking about using a laser pointer, the visible dot is the point where the photons are striking, so it's exactly analogous to the point of impact for the bullets.


This, I hope, makes the issue clearer.
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Re: A question on the speed of light

Postby Azrael001 » Sun Mar 02, 2008 7:23 am UTC

It does, and the bullets analogy was the thing that I was trying to think of earlier. I now agree with you, I was thinking about the possibility that while the dot would seem to move at speed > C would it not loose quality (quality is probably the wrong word) over the distance and, like the bullets, end up leaving gaps where the light did not hit? If not at 1 AU then at some greater distance?

(This is just a genuine question and not any kind of continuation of an argument.)
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Re: A question on the speed of light

Postby SpitValve » Sun Mar 02, 2008 1:32 pm UTC

Owehn wrote:If I have a laser pointing at a distant object and start to turn the laser, then yes, the spot will take as long to start moving as it took the light to get there. But the speed at which the spot moves (once it does) increases linearly with the distance to the object, so for a far enough object the spot will move faster than light.


Yep, and there's nothing wrong with that, because through this method no information can be transmitted at faster than the speed of light. It's not a physical object that's moving, so it doesn't obey the lorentz transforms and you're ok.

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Re: A question on the speed of light

Postby EricH » Sun Mar 02, 2008 5:11 pm UTC

Azrael001 wrote:It does, and the bullets analogy was the thing that I was trying to think of earlier. I now agree with you, I was thinking about the possibility that while the dot would seem to move at speed > C would it not loose quality (quality is probably the wrong word) over the distance and, like the bullets, end up leaving gaps where the light did not hit? If not at 1 AU then at some greater distance?

(This is just a genuine question and not any kind of continuation of an argument.)


Ah, now I see where you're going; to answer your question, yes--since the photons are coming out at a constant rate, the faster you move the laser, the less light strikes any one point. So, you could move the dot at such a speed as to have a measurable distance between the location struck by a photon and the location struck by the next. Hmm. For 'measurable,' substitute 'arbitrarily large.' Though you probably wouldn't be calling it a dot, any more, as it would be too dim to see, and at too great a distance for the laser beam to still be considered coherent.
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Re: A question on the speed of light

Postby antonfire » Sun Mar 02, 2008 8:17 pm UTC

SpitValve wrote:
Owehn wrote:If I have a laser pointing at a distant object and start to turn the laser, then yes, the spot will take as long to start moving as it took the light to get there. But the speed at which the spot moves (once it does) increases linearly with the distance to the object, so for a far enough object the spot will move faster than light.


Yep, and there's nothing wrong with that, because through this method no information can be transmitted at faster than the speed of light. It's not a physical object that's moving, so it doesn't obey the lorentz transforms and you're ok.
Well, no, it obeys the Lorentz transforms. And in some frames of reference, it travels backwards. It's just that this no longer creates an issue of causality.
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Re: A question on the speed of light

Postby SpitValve » Sun Mar 02, 2008 10:26 pm UTC

antonfire wrote:
SpitValve wrote:Yep, and there's nothing wrong with that, because through this method no information can be transmitted at faster than the speed of light. It's not a physical object that's moving, so it doesn't obey the lorentz transforms and you're ok.
Well, no, it obeys the Lorentz transforms. And in some frames of reference, it travels backwards. It's just that this no longer creates an issue of causality.


yeah, sorry, didn't think that one through. They're just a series of events separated by spacelike intervals, you can transform them fine.

But if you consider say, a rotating laser beam hitting a sphere such that the point of intersection is moving faster than the speed of light, you can not use the Lorentz transforms to transform into the frame of that moving point. That's what I meant to say...

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Re: A question on the speed of light

Postby Korandder » Sun Mar 02, 2008 10:42 pm UTC

SpitValve wrote:
ekzrated wrote:I see what you did there. But if we're discussing things in terms of general relativity, what does it matter how fast light goes when you'er thinking in galaxy-sized proportions? Surely there's more to it than light.


I don't get what you mean. We see something 8 billion light years away, then we're seeing what it looked like 8 billion years ago. That's pretty important.


When we look at some thing that is now 8 billion light years away we do not see it as it was 8 billion light years ago since the universe is expanding.

Consider an Einstein de Sitter universe and a galaxy with a redshift of z = 1. We observe this galaxy as it was 6 billion years ago however this galaxy is now 8 billion light years away.
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Re: A question on the speed of light

Postby SpitValve » Mon Mar 03, 2008 12:43 am UTC

Korandder wrote:
SpitValve wrote:I don't get what you mean. We see something 8 billion light years away, then we're seeing what it looked like 8 billion years ago. That's pretty important.


When we look at some thing that is now 8 billion light years away we do not see it as it was 8 billion light years ago since the universe is expanding.

Consider an Einstein de Sitter universe and a galaxy with a redshift of z = 1. We observe this galaxy as it was 6 billion years ago however this galaxy is now 8 billion light years away.


I was hoping to sweep that under the rug :) yeah, the proper distance to a galaxy with a lookback time of 6 billion years is not 6 billion light years. But because the photon travelled for 6 billion years, it has travelled a distance of 6 billion light-years, and that's the distance that you can calculate with the cosmological redshift. It's not the current proper distance to the galaxy, but it's still a useful concept.

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Re: A question on the speed of light

Postby genewitch » Mon Mar 03, 2008 9:26 pm UTC

SpitValve wrote:
ekzrated wrote:I see what you did there. But if we're discussing things in terms of general relativity, what does it matter how fast light goes when you'er thinking in galaxy-sized proportions? Surely there's more to it than light.


I don't get what you mean. We see something 8 billion light years away, then we're seeing what it looked like 8 billion years ago. That's pretty important

ekzrated wrote: I mean, if we look at the solar system and compare it to an atom, there's definitely similarities,


Nope!

Spoiler:
Similarities between an atom and the solar system:

1. Large massive object in the centre with a force inwards towards it
2. Small objects "orbiting" around that object

Differences:

1. Electrons can only occupy discrete energy levels, planets can orbit any way they want
2. Planets are attracted to other planets, electrons repulse other electrons (gravity is always attractive, electrostatic force is sometimes attractive and sometimes repulsive)
3. Electrons are best described by a wavefunction, where momentum and position can not be well-defined at the same time. A planet can have a definite momentum and a definite position
4. An electron is (as far as we know) indivisible, and has no real "size". Planets have lots of substructure, can be split apart, joined, exploded, they have clouds, mountains, seas, sand, people etc
5. Planets have moons and things
6. Large groups of star systems look like star clusters and galaxies. They never form a regular lattice structure like a crystal of atoms can form.

and so on. Basically: there is not really all that in common, and any philosophy based on "solar systems/galaxies might be atoms in another universe" is simply wrong.


and really speed and time wouldn't mean anything if we talk relativity.


Speed and time do have meaning in relativity. They follow quite definite laws. They're just not the same laws you're used to.


This idea of the solar system atom came from the early encyclopedia entries of "atom." i distinctly remember our set of encyclopedias from the fifties when i was growing up. even my grade school explanations of atoms had the "orbits" and such. My girlfriend's chemistry course in a university uses this diagram to map out what electrons are where and how many. I don't recall the exact year but i want to say it was somewhere between 1910 and 1925 that this diagram was first used.

Nowadays, from what i've seen, atoms look like a checkerboard pattern used as a height map in a 3d program... a really distorted ball of probabilities. I find the whole thing fascinating, because in my lifetime so far the science has progressed so far that it's easier to explain what's really going on than to try and use the "solar system" analogy. electrons don't really orbit the neutrons and proton nuclei, they form a "shell" of probabilities. Hence my checkerboard analogy. For any given position, you can state with arbitrary precision how likely an electron is to "be there" - as long as that probability is less than 1.

I'm probably not making any sense so i'll stop now. Feynman and Hawking and Sagan do a much better job than i do of explaining such things. :-D
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Re: A question on the speed of light

Postby evilbeanfiend » Mon Mar 03, 2008 9:49 pm UTC

genewitch wrote:This idea of the solar system atom came from the early encyclopedia entries of "atom." i distinctly remember our set of encyclopedias from the fifties when i was growing up. even my grade school explanations of atoms had the "orbits" and such. My girlfriend's chemistry course in a university uses this diagram to map out what electrons are where and how many. I don't recall the exact year but i want to say it was somewhere between 1910 and 1925 that this diagram was first used.


isn't it exactly the rutherford model? so that would date it around 1910
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Re: A question on the speed of light

Postby thoughtfully » Wed Mar 05, 2008 6:01 pm UTC

It's more correctly the Bohr model. Rutherford didn't establish any characteristics of the electron, except that they were buzzing around well outside the nucleus somewhere. Bohr established the familiar model with circular orbits in two dimensions, where the electron was constrained to orbits in which a full multiple of its deBroglie wavelength could fit, which quantized the energy states.

It's worth noting that the Bohr model only yielded good results for the Hydrogen atom (an amazing enough feat, at the time), until extended by Sommerfeld to include Special Relativity, which served somewhat better, until Shrodinger came along and schooled em all.

EDIT: Rutherford did propose a similar model, earlier than Bohr, although his was more suggestive, rather than deriving characteristics based on previous theoretical or experimental results, although he does cite a broadly similar model proposed by a Japanese physicist in 1904. Notably, the Rutherford Model makes few new predictions. Now my head is spinning, not merely the electrons!

Rutherford's model is the model used most often for pictorial representations. I stand corrected on that point.
Although, it seems that Bohr's shows up more in schematic (as opposed to symbolic) representatioins, such as chemical contexts.

Another Edit: this page sums it up nicely: http://nobeliefs.com/atom.htm
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Re: A question on the speed of light

Postby ekzrated » Fri Mar 14, 2008 3:47 pm UTC

So, basically then since nothing faster has been discovered, we're sticking to "speed of light is the fastest" theory.

It'd be interesting to live to see it get outclassed.
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Re: A question on the speed of light

Postby Owehn » Fri Mar 14, 2008 3:51 pm UTC

ekzrated wrote:So, basically then since nothing faster has been discovered, we're sticking to "speed of light is the fastest" theory.

It'd be interesting to live to see it get outclassed.


Sort of. Relativity has also predicted other effects (simplest being time dilation, and up there with most complicated being the extreme accuracy of QED) which have been experimentally verified, so we're sticking to "relativity is valid, or very close to it". Since relativity also predicts that being able to send information faster than light would violate causality, we're sticking to "speed of light is the fastest."
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Re: A question on the speed of light

Postby Charlie! » Sat Mar 15, 2008 2:32 am UTC

ekzrated wrote:So, basically then since nothing faster has been discovered, we're sticking to "speed of light is the fastest" theory.

It'd be interesting to live to see it get outclassed.

Yup, that's how science works :-D

However, that doesn't mean that relativity is somehow tenuous. In fact, it's got tonnes of support. And we can't rule out anything, but after the first few thousand times you try to falsify a hypothesis and come up blank, you can assume pretty safely that it holds for situations similar to those tested.
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Re: A question on the speed of light

Postby edge walker » Sat Mar 15, 2008 7:22 pm UTC

ekzrated wrote:So, basically then since nothing faster has been discovered, we're sticking to "speed of light is the fastest" theory.

It'd be interesting to live to see it get outclassed.

Not exactly. It’s more like: the laws of physics as we currently understand them rule out the possibility of anything traveling faster than light. Now, our understanding of physics is not complete, and it may yet happen that we will find some exception that allows faster-than-light travel in particular circumstances. However, the theories we already have are extremely well-tested, so even in the event that we discover circumstances under which different laws hold, these circumstances will be extraordinarily limited and will probably not be very useful in terms of technological use. (Don’t forget we’re still trying to find a way to make use of superconductivity. Hell, we are forever “no more than 50 years away” from successfully creating sustained controlled nuclear fusion, and that’s not even based on exotic physics.)

We never really know, of course; but our uncertainty ever diminishes.

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Re: A question on the speed of light

Postby Tchebu » Sun Mar 16, 2008 6:19 am UTC

If A then B, so
if not B then not A.

In relativity it's
If speed of light is constant for all observers then nothing can move faster than light
so if something CAN move faster than light then light shouldn't move at a constant rate for all observers.

As far as we can tell, light speed is pretty constant. And I think performing the Michaelson experiment more and more precisely is easier than trying to look for something that moves faster than light (or even worse, accelerating something to that speed), so I think we'll see a change in speed of light before we will even come close to finding what is it exactly that moves faster than light.

This got me thinking...
How much will we have to fix if the Michaelson experiment gives a positive result at one more decimal point than has so far been performed?
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Re: A question on the speed of light

Postby Iv » Sun Mar 16, 2008 10:48 am UTC

ekzrated : long story short : verified equations show us that the energy required to bring an object to the speed of light is infinite.

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Re: A question on the speed of light

Postby edge walker » Sun Mar 16, 2008 11:15 am UTC

Tchebu wrote:This got me thinking...
How much will we have to fix if the Michaelson experiment gives a positive result at one more decimal point than has so far been performed?

See my reply above: in some senses, not a whole lot. It would be similar to Einstein’s job, who had to fix Newtonian physics to get something that’s valid in more regimes. Likewise if we found that speed of light is not constant across all frames of reference, someone would have to fix Einsteinian physics to get something that’s valid in more regimes. But because of how much experimental confirmation we have of relativity, this new regime must necessarily be, in some sense, tiny. Any new theory would not change the validity of relativity for the regimes in which it has already been well-tested, just as relativity did throw Newtonian physics out the window, just constrained the regime in which they are applicable.

So yes, in some sense, experimentally finding a contradiction to relativity would be huge news; but under the bottom line, it wouldn’t change all that much.

Iv wrote:ekzrated : long story short : verified equations show us that the energy required to bring an object to the speed of light is infinite.

With what device can you measure infinite energy? ;)

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Re: A question on the speed of light

Postby Tchebu » Sun Mar 16, 2008 5:30 pm UTC

Infinitenergyrometer?
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Re: A question on the speed of light

Postby btarlinian » Sun Mar 16, 2008 8:34 pm UTC

edge walker wrote:
Iv wrote:ekzrated : long story short : verified equations show us that the energy required to bring an object to the speed of light is infinite.

With what device can you measure infinite energy? ;)


In all seriousness though, you obviously can't measure an infinite amount of energy. However, you can measure the energy it takes to get a particle up to a specific fraction of the speed of light and then numerically conclude that as the speed of the particle approaches the speed of light, the the energy of the particle tends to infinity.


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