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dvb
2003-Dec-19, 04:59 AM
Ok, I have a question that has more questions to it. This is my first post on here, and I already did a forum search to see if anyone else has made any posts about what I'm going to discuss here.

I've read a few posts on the fabric of space, and what that fabric is actually made up of. It seems that no one really knows, and whether anything makes it up at all is still in question. We know that the speed of light is roughly 300,000km per second, and that matter can slow it down such as water and other things.

I think my question has more to do with why can't light go any faster than 300,000kps. Friction holds things back from going beyond certain speeds in the earths atmosphere, but in outer space there is no friction, so why can't the speed of light continue to accelerate? Could there be some properties in the fabric of space putting a speed limit on everything? I understand that the amount of energy used is directly affected by the speed at which something travels. Wouldn't this hold true for the speed of light as well? We can deccerate light, so why not accelerate it?

Maybe I have no idea what I'm talking about. I'll probably leave this post with more questions remaining than answered, but it's always something to ponder. If there was some properties to the fabric of space, then it would be possible we could manipulate it.

freddo
2003-Dec-19, 05:34 AM
Hi dvb, welcome a-board.. :wink:

You're right that this kind of topic will likely raise more questions than it answers - as a lot of this deals with relativity - which can be a headful to understand.

One of the main principles is that the speed of light is always constant regardless of the speed of the observer. So it is always travelling at c. This means if you measure it as going slower (like through glass) there must be something else happening in order for us to account for the change in measured speed. Enter relativity, which postulates that space and time may not be quite what they seem...

This is a start - I'm sure others will elaborate further.

Jobe
2003-Dec-19, 05:58 AM
I think my question has more to do with why can't light go any faster than 300,000kps. Friction holds things back from going beyond certain speeds in the earths atmosphere, but in outer space there is no friction, so why can't the speed of light continue to accelerate? Could there be some properties in the fabric of space putting a speed limit on everything? I understand that the amount of energy used is directly affected by the speed at which something travels. Wouldn't this hold true for the speed of light as well? We can deccerate light, so why not accelerate it?


Diclaimer: I'm not a physicist and could be completely wrong about this.

I think the idea is this, the speed of light is a constant. A feature of the universe. Einstein factored it in to our view by saying

e = mc^2

where e = energy
m = mass
c = speed of light

Light doesn't accelerate, or decelerate, it just travels at the speed of light. When light passes through a medium like water, the refractions make lights path longer, but it still travels between interactions with the atoms at the speed of light. This is why the overall pulse appears to slow down, its travelling further.

As something WITH mass accelerates and gets closer to the speed of light, its mass increases. As its mass increases, it will be harder to accelerate. If you plug in values for light speed into something with mass, I believe its mass becomes infinite, hence the light speed barrier.

Hope this helps. Those in the know feel free to smack me down.

dvb
2003-Dec-19, 06:01 AM
Thanks for your reply freddo! :)

I've studdied the theory of relativity, and understand some of it. I was just wondering more along the lines of what makes the speed of light what it is. I'm guessing there must be some barrier. Something holding it back from going faster. I think maybe the fabric of space could be the key. If only we could control it.

Just throwing out more thoughts on the subject. ;)

Jobe
2003-Dec-19, 06:04 AM
Oh yeah to add to the complications.

Light is the same speed for all observers.

So in other words, if you're in a train travelling at velocity v relative to someone "stationary" on the embankment in front of you, and you fire a light pulse towards this person, you would expect the light to travel at c relative to you, but to the person on the embankment, you would expect it to travel c + v.

However, it doesn't. It travels at c as far as both of you are concerned.

So given the newtonian equation

d = v.t

distance = velocity x time

If the velocity remains constant, then distance and time must change. Thats where you get into the spacetime warping and things become confusing. :P

dvb
2003-Dec-19, 06:04 AM
Thank you for your thoughts as well Jobe! I thought that light could be decelerated, but it makes sense the way you explain it with water only making the path longer.

dvb
2003-Dec-19, 06:12 AM
Ok, I understand how light maintains a constant speed no matter what velocity you're traveling at. But does anyone know what makes the speed of light constant, and why it's the speed that it is? I think if we knew the answer to this, we'd have a much better understanding of the universe. :)

pmcolt
2003-Dec-19, 06:22 AM
The speed of light (in free space, or through a medium) can be determined by the electric constant (permittivity) and magnetic constant (permeability) of the medium. This is because light is the result of interacting electric and magnetic fields, whose behavior can be predicted with Maxwell's equations.

It's not exactly that "friction" prevents light from accelerating; the speed of light is determined by certain measurable physical properties of whatever it's passing through. For free space, these properties are fundamental constants, as far as I know. If there were some way of altering universal constants at will, I bet it would cause all sorts of theories to fall apart. But then, I'm not a physicist, so I wouldn't know for sure.

Edit: oops. welcome to the board, dvb :)

dvb
2003-Dec-19, 06:44 AM
Hello pmcolt. Thanks for your welcome!

I don't know much about maxwell's equations, but I guess I have some reading up to do on them now. This all seems to be slowly going over my head lol.

You say that the properties of free space are fundamental constants, but wouldn't these constants be derived from the properties of free space itself? In other words, if we knew what made up free space i.e. dark matter or some other crazy theory, then manipulating those properties would change the constants. My explanation all sounds very redundant here, and maybe I don't know what I'm talking about, but I'm trying. :)

Lets just say that it's not really the speed of light that I'm most interested in, it's more about what we don't now about the fabric of space. I'm using the speed of light as an example to understand the fabric of space. I think if we were to learn more about this emptyness, then the speed of light would be the first step in figuring out what empty space is made up of. Follow? :)

pmcolt
2003-Dec-19, 07:19 AM
Hmmm. The properties of free space are derived from properties of free space, which are derived from properties of free space, which... and it's turtles all the way down, right? :)

All right, seriously, I think I follow. If I understand, the question boils down to: what exactly is empty space, why does it act the way that it does, and can we control the way that it acts? As a computer engineering student, the grand mysteries of existence are a bit fuzzy for me, but I'll give it a try.

What do we know about the universe? Well, it's pretty big, mostly empty, and has a grudge against me. And there's this weird thing called space. Even though it's usually "empty", it still has certain properties that control how it behaves. It can (and does) expand on a universal scale. Gravity can influence it and bend it. Electromagnetic fields, other forces, and matter can pass through it in ways controlled by its properties.

So the question is; what makes these properties what they are? Or alternately, what exactly is space, that it behaves the way that it does? As far as I know, we haven't figured out why the fundamental constants have the values that they have, but I bet that would go a long way toward answering the question.

dvb
2003-Dec-19, 07:39 AM
Hmmm. The properties of free space are derived from properties of free space, which are derived from properties of free space, which... and it's turtles all the way down, right? :)

LMAO! I know I was very redundant, but I decided to leave it in there for a lack of better words.

It's the properties of empty space that I find very interesting. If only some day, in the near future, we could figure out what the heck it was and how to manipulate it. I truely think that what this emptyness is made up of is the key to the universe. Ok, maybe I watch too much star trek, but it's always nice to hope that maybe we could tear a hole in the fabric of space and come out in another galexy! :D

Edit: or another time for that matter

ToSeek
2003-Dec-19, 04:24 PM
The uncertainty principle allows for "virtual particles" that can pop in and out of existence, so if you look very closely at empty space what you actually see (in a metaphorical sense) is a sort of quantum foam of particles just barely on the edge of existence. It's thought by some that this foam interacts with electromagnetic radiation and slows it down. If there were some way of suppressing this foam somehow (as with the Casimir effect), it might be possible to make something move faster than what we know as the speed of light.

Relevant news article:
Einstein makes extra dimensions toe the line (http://www.spaceflightnow.com/news/n0312/16einstein/)

dvb
2003-Dec-20, 01:14 AM
Thank you very much ToSeek!!!

That article really clears things up for me and answers a lot of my questions. :D

Sam5
2003-Dec-20, 01:40 AM
I think my question has more to do with why can't light go any faster than 300,000kps. Friction holds things back from going beyond certain speeds in the earths atmosphere, but in outer space there is no friction, so why can't the speed of light continue to accelerate? Could there be some properties in the fabric of space putting a speed limit on everything? I understand that the amount of energy used is directly affected by the speed at which something travels. Wouldn't this hold true for the speed of light as well? We can deccerate light, so why not accelerate it?


Just an opinion. I suggest the “fabric” is made up of the “fields”, the magnetic, electric, and gravitational fields generated by astronomical bodies. Otherwise, in my humble opinion, space would be empty. And I also believe that these fields regulate the speed of light to approximately “c”. Of course, according to both theory and observation, it slows down when it enters a strong local gravitational field.

kilopi
2003-Dec-20, 01:49 AM
Friction holds things back from going beyond certain speeds in the earths atmosphere, but in outer space there is no friction, so why can't the speed of light continue to accelerate? Could there be some properties in the fabric of space putting a speed limit on everything?
In the case of sound, and the speed of sound, it's not exactly friction that is "slowing" it down. The speed of sound is much greater in some heavy dense materials. Although there are some losses due to friction, the speed of sound doesn't really depend upon it that much.

As in an automobile, where we try to reduce friction by using oil, without the friction between tire and road, we wouldn't be able to climb a hill with a car.

dvb
2003-Dec-20, 01:58 AM
Thank you both for your insight!

I understand your analogy kilopi. Are you saying that light would require a certain friction of some sort for it to reach the speeds that it does? Similar to how a car needs a road to travel on in order for it to move forward.

kilopi
2003-Dec-20, 02:12 AM
I understand your analogy kilopi. Are you saying that light would require a certain friction of some sort for it to reach the speeds that it does? Similar to how a car needs a road to travel on in order for it to move forward.
Hmm, that would seem to be some sort of ether, wouldn't it?

Sometimes, analogies are only heuristic. :)

Sam5
2003-Dec-20, 02:33 AM
dvb,

I agree. What an excellent example for the need of an "ether". And I think the “fields” act as that “ether” to regulate the speed of light.

If light had just “empty space” to travel through, it would have nothing by which to determine how fast or slow it should move.

kilopi
2003-Dec-20, 02:36 AM
dvb,

I agree. What an excellent example for the need of an "ether". And I think the “fields” act as that “ether” to regulate the speed of light.

If light had just “empty space” to travel through, it would have nothing by which to determine how fast or slow it should move.
Does space determine how fast or slow atoms move, in a gas?

Sam5
2003-Dec-20, 02:41 AM
Thank you both for your insight!

I understand your analogy kilopi. Are you saying that light would require a certain friction of some sort for it to reach the speeds that it does? Similar to how a car needs a road to travel on in order for it to move forward.

In fact, I’m going to use that “friction between the tire and the road” example in all my future lectures about the “ether”. What an excellent analogy.

kilopi
2003-Dec-20, 02:48 AM
in all my future lectures about the “ether”.
I did it again!

dvb
2003-Dec-20, 06:00 AM
Ok, you guys got the wheels spinning in my head again now. If we could push these magnetic and electric fields out of the way with say a superconductor and allow the light to travel through free space uninterrupted by the fields, could we then accelerate it? Or are the fields far too strong to manipulate?

Grey
2003-Dec-20, 06:23 AM
You say that the properties of free space are fundamental constants, but wouldn't these constants be derived from the properties of free space itself? In other words, if we knew what made up free space i.e. dark matter or some other crazy theory, then manipulating those properties would change the constants.
I'll drop in to point out that there are currently no theories that successfully predict the values of most of the constants of nature from first principles. There are a fair number of such constants, and as far as we can tell they seem to be unchangable, but of course since we can't explain why they have the values we measure, you're correct that we can't be absolutely certain there is no way to alter them.

dvb
2003-Dec-20, 07:52 AM
Very interesting Grey!

Would you be able to elaborate a bit more on what these constants are? Is the speed of light one of them?

kilopi
2003-Dec-20, 09:37 AM
Is the speed of light one of them?
Yes and no. :)

Ever since Einstein's "axiomization" of special relativity (http://www.fourmilab.ch/etexts/einstein/specrel/www/), the speed of light has been considered a fundamental constant. In fact, the meter is defined so that the speed of light is exactly 299792458 meters per second (http://www.xs4all.nl/~jcdverha/scijokes/11_4.html#6).

However, I'd imagine one of the great moments in the history of science was when Maxwell played with his equations, using the constants permittivity (http://dictionary.reference.com/search?q=permittivity) of free space (http://scienceworld.wolfram.com/physics/PermittivityofFreeSpace.html) and the permeability (http://dictionary.reference.com/search?q=permeability) of free space (http://scienceworld.wolfram.com/physics/PermeabilityofFreeSpace.html), and found that the speed of electromagnetic waves would be the square root of the reciprocal of their product--and that that speed was also the speed of light. In that sense, he had taken two known constants, and developed a theory from which he could successfully derive a third constant. But, as Grey would agree I'm sure, that doesn't explain the first two.

Was a step in the right direction though. :)

Chip
2003-Dec-20, 11:01 AM
I'll drop in to point out that there are currently no theories that successfully predict the values of most of the constants of nature from first principles. There are a fair number of such constants, and as far as we can tell they seem to be unchangable, but of course since we can't explain why they have the values we measure, you're correct that we can't be absolutely certain there is no way to alter them.

Hmmmm...something for the next Einstein to come along: A "Theory of the Value of Constants." :wink:

dvb
2003-Dec-20, 11:16 AM
Thank you for the links kilopi. :)

I took a look at the definitions of permittivity and permeability, but none of it seems very easy to understand. I did a few google searches looking for some real world examples, but came up with nothing within my grasp.

I don't mean to be a nag, I just feel a little intimidated by some of these big words. Could someone break down the definitions using real world examples of how I could better understand what permittivity and permeability is.

Permittivity: A measure of the ability of a material to resist the formation of an electric field within it.

In other words how well a certain mass or matter repells the effects of an electric field that it generates?

Permeability: The rate of flow of a liquid or gas through a porous material

This definition seemed to make the most sense even though I don't believe it's the exact definition we'd be using in free space. Could this be reworded to mean the speed at which matter or energy travel through space?

I'm a quick learner, I just have troubles catching onto concepts sometimes. I see these 2 words pop up quite often, and I feel left out in a lot of the conversations because I can't grasp the concepts.

kilopi
2003-Dec-20, 11:58 AM
Oops, I included multiple links in that post--the "free space" links are to the World of Science discussions about the parameters. Instead of the dictionary definition of permeability, we probably should be starting with magnetic permeability (http://dictionary.reference.com/search?q=magnetic%20permeability).

In a simple capacitor, there are two plates separated by an insulator, the dielectric. Sometimes the dielectric is just air. The "capacity" of the capacitor is affected by the property called the dielectric constant--which is also called the electric permittivity. The corresponding quantity for magnetism is the permeability.

Sam5
2003-Dec-20, 02:38 PM
I'll drop in to point out that there are currently no theories that successfully predict the values of most of the constants of nature from first principles. There are a fair number of such constants, and as far as we can tell they seem to be unchangable, but of course since we can't explain why they have the values we measure, you're correct that we can't be absolutely certain there is no way to alter them.

Have you ever considered that since just about all of the 19th Century experiments in electrodynamics were conducted at the surface of the earth, the earth’s own gravitational field and field potential at the places where the experiments were conducted could have influenced the results of the experiment? For example, the Michelson Morley experiment failed to turn up any evidence that the earth-relative speed of light slows down when photons pass near the sun. Also, it did not turn up any results that indicated the gravitational redshifting of light that is emitted from the surface of the earth, as measured several meters above the surface. This redshifting wasn’t observed until Pound and Rebka conducted their Harvard Tower experiment in 1960, using a vertically oriented apparatus rather than a horizontally oriented one.

Grey
2003-Dec-20, 06:09 PM
Would you be able to elaborate a bit more on what these constants are? Is the speed of light one of them?
I'll completely agree with kilopi about whether you should consider the speed of light a fundamental constant, or whether the permittivity and permeability of free space should be considered more fundamental. Other values are things like the elementary unit of charge or the mass of an electron. There are also dimensionless constants, like the fine structure constant (http://scienceworld.wolfram.com/physics/FineStructureConstant.html). I've also heard some discussion (http://arxiv.org/abs/physics/0110060) about whether the constants with dimensions should really be considered meaningful, or whether they're just arbitrary conversion factors because of our choice of units that we use.


Hmmmm...something for the next Einstein to come along: A "Theory of the Value of Constants."
Indeed, I'd say it's almost certain that if someone could come up with a way to explain almost any of these constants from first principles, that would make them a likely candidate for a Nobel.


Have you ever considered that since just about all of the 19th Century experiments in electrodynamics were conducted at the surface of the earth, the earth’s own gravitational field and field potential at the places where the experiments were conducted could have influenced the results of the experiment? For example, the Michelson Morley experiment failed to turn up any evidence that the earth-relative speed of light slows down when photons pass near the sun. Also, it did not turn up any results that indicated the gravitational redshifting of light that is emitted from the surface of the earth, as measured several meters above the surface. This redshifting wasn’t observed until Pound and Rebka conducted their Harvard Tower experiment in 1960, using a vertically oriented apparatus rather than a horizontally oriented one.
It's possible of course. However, it's unlikely that, say, the speed of light changes measurably within the solar system, since we'd notice in the observational delays of eclipses of the Jovian moons, say, or varying times in occultations. Similarly, if the constants that govern the behavior of electricity and magnetism changed away from Earth, we'd see problems with some of our distant spacecraft which are certainly closer to the gravitational wells of other planets.

There have been no experiments that have violated the predictions of general relativity or quantum mechanics (anyone who successfully showed such a violation would very likely also be a Nobel candidate), so while we're free to speculate about possible modifications to those theories, any such modifications would have to make the same predictions in all the domains that have been tested.

kilopi
2003-Dec-20, 06:29 PM
I've also heard some discussion (http://arxiv.org/abs/physics/0110060) about whether the constants with dimensions should really be considered meaningful, or whether they're just arbitrary conversion factors because of our choice of units that we use.
Yes, for instance, the speed of light, which seems to convert measurements in the time dimension into spatial units. If our perception of time were equivalent to our perception of space, then the speed of light would be 1 (some take that point of view exactly), with no units at all.

The next question, though, would be why our perception is different then? Or, at least, we perceive it to be different. :)

dvb
2003-Dec-20, 08:54 PM
Thank you for the clarifications kilopi!


Yes, for instance, the speed of light, which seems to convert measurements in the time dimension into spatial units. If our perception of time were equivalent to our perception of space, then the speed of light would be 1 (some take that point of view exactly), with no units at all.

The next question, though, would be why our perception is different then? Or, at least, we perceive it to be different. :)

This is a very interesting concept. I have another question now. They say that radio waves travel at or near the speed of light, and also electrons orbiting around the nucleus of an atom. There seems to be a lot of things that travel at the speed of light, but why is the speed of light the reference point to all of these?

If the electrons in all matter travel at this speed, wouldn't it put everything out of space-time? Or maybe this means something else entirely.

swansont
2003-Dec-20, 10:15 PM
This is a very interesting concept. I have another question now. They say that radio waves travel at or near the speed of light, and also electrons orbiting around the nucleus of an atom.

Radio waves always travel at the speed of light, by definition - they are electromagnetic radiation. Electrons, however, never do.

dvb
2003-Dec-20, 10:43 PM
This is a very interesting concept. I have another question now. They say that radio waves travel at or near the speed of light, and also electrons orbiting around the nucleus of an atom.

Radio waves always travel at the speed of light, by definition - they are electromagnetic radiation. Electrons, however, never do.

Thank you for the clarification. I thought I read somewhere in a physics book that electrons travel at the speed of light. Any idea what speed they travel at?

Grey
2003-Dec-21, 01:59 AM
Thank you for the clarification. I thought I read somewhere in a physics book that electrons travel at the speed of light. Any idea what speed they travel at?
Since they are particles that have mass, they can theoretically be moving at any speed from zero up to just less than the speed of light, just like any other object. Since they are charged and very light, they're pretty easy to accelerate to high speeds though. I think that the electrons in a cathode ray tube (like your monitor, if you don't have one of those flashy flat panel screens) are typically accelerated to about 10% the speed of light. Electrons can't really be said to orbit the nucleus of an atom like a particle, but if they did, the orbital velocity of an electron in a hydrogen atom would be about 0.7% the speed of light. On the other hand, the speed of electrons travelling in a wire as electricity flows is actually quite slow, on the order of centimeters per hour.

dvb
2003-Dec-21, 09:35 PM
Thanks again grey. :)