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I have always had a problem with the speed of light. Not why is it constant but, why is it 300,000 km/s? Why isn't it 301,000 km/s? No one seems to be pursuing the answer to this, which I consider a very interesting question. My personal hypothesis is that the speed of light is tied to the expansion rate of the universe. Interestingly enough, Hubble's constant gives an expansion rate of the universe that equals c at a distance equivalent to the age of the universe in lightyears (i.e. the age of the universe is estimated at 13.8 billion years old and the distance at which objects are moving away from us at the speed of light is estimated at 13.8 billion lightyears). Now, that seems like way to unlikely a coincidence. And, do you see how the speed of light being directly proportional to the expansion rate of the universe would make sense? Since nothing can leave the universe, thereby limiting light and everything else to 300,000 km/s. So, the fact that 300,000 km/s being the speed of light would really only be a corollary to the reason that it can't go any faster, which would be the expansion rate of the universe. In other words, c only reflects the fact that the expansion rate of the universe is 300,000 km/s. Am I missing something? Is this a "duh" moment rather than an "Ahah!" moment?

If this is not a "duh" moment, then things get really interesting in that any change in the expansion rate of the universe would be reflected in a change in the speed of light. And, even more interesting is what would happen if the universe ever decided to start shrinking??!?!

Thanks and best regards,

Windjammer

Units are man-made conventions to aid in communications, typically associated with commerce, surveying and engineering. In physics, these conventions don't matter and the speed of light is written as "c" to write universal truths which work in any units, or sometimes natural units are adopted with the convention c = 1 and factors of c are omitted just like in factoring a number factors of 1 are omitted.

But you are mistaken to assign significance to 300000 km/s -- that is not the exact speed of light.

It's exactly 299792.458 km/s or exactly 186282 miles 2096 feet and 5 21/127 inches per second.

http://www.physforum.com/index.php?showtop...ndpost&p=194391

http://en.wikipedia.org/wiki/Speed_of_light#cite_note-12

This is because the international definition of the mile is exactly 1609.344 km http://physics.nist.gov/Pubs/SP811/appenB8.html#M The US adopted this international convention in 1959.

Federal Register, Vol. 24, No. 128, p. 5348, July 1, 1959

Which has since been codified as C.F.R. 16 § 500.19 [PDF]

And because the international definition of the meter*used to be* a particular metal bar measured under certain conventions. But it was error-prone to make that measurement and the metal bar could be damanged/corrode/be stolen and so a higher precision and more portable definition of meter in 1983. So the speed of light in vacuum can have no other value than 299792.458 km/s because that was a choice made by men to further communication in commerce, engineering and surveying. It was a choice most compatible with early decisions made in 1793, 1889, and 1960.

http://en.wikipedia.org/wiki/Metre

But you are mistaken to assign significance to 300000 km/s -- that is not the exact speed of light.

It's exactly 299792.458 km/s or exactly 186282 miles 2096 feet and 5 21/127 inches per second.

http://www.physforum.com/index.php?showtop...ndpost&p=194391

http://en.wikipedia.org/wiki/Speed_of_light#cite_note-12

This is because the international definition of the mile is exactly 1609.344 km http://physics.nist.gov/Pubs/SP811/appenB8.html#M The US adopted this international convention in 1959.

Federal Register, Vol. 24, No. 128, p. 5348, July 1, 1959

Which has since been codified as C.F.R. 16 § 500.19 [PDF]

And because the international definition of the meter

http://en.wikipedia.org/wiki/Metre

You're missing the point. I don't really care if it's two km/s. The point is that it is some velocity and it is that velocity for a reason. No one has a clue what that reason is. And, no one really seems to have much interest in investigating it.

QUOTE (windjammer+Aug 4 2011, 10:00 PM)

You're missing the point. I don't really care if it's two km/s. The point is that it is some velocity and it is that velocity for a reason. No one has a clue what that reason is. And, no one really seems to have much interest in investigating it.

My understanding is that the current thinking is that when we figure out the Theory of Everything that unites quantum and relativistic physics, the 'reason' for constants like G, c and h will be found there. So, yes, why c is what it is*is* being studied, just not under its own banner.

My understanding is that the current thinking is that when we figure out the Theory of Everything that unites quantum and relativistic physics, the 'reason' for constants like G, c and h will be found there. So, yes, why c is what it is

windjammer;

James Clerk Maxwell (1831-1879) had a clue what the reason is.

Read up on the vacuum permittivity and the vacuum permeability.

http://en.wikipedia.org/wiki/Vacuum_permittivity

http://en.wikipedia.org/wiki/Vacuum_permeability

In the permeability link, go to the Significance in Electromagnetism section, and do the speed of light equation.

James Clerk Maxwell (1831-1879) had a clue what the reason is.

Read up on the vacuum permittivity and the vacuum permeability.

http://en.wikipedia.org/wiki/Vacuum_permittivity

http://en.wikipedia.org/wiki/Vacuum_permeability

In the permeability link, go to the Significance in Electromagnetism section, and do the speed of light equation.

You can't investigate a perfect symmetry of nature. If the symmetry is perfect, then all mathematical models of that symmetry are equivalent. If all mathematical models are equivalent then no experiment will favor one over another. So the best you can do is write the simplest description of the perfect symmetry.

"The hyperbolic geometry of space-time naturally associates the invariant speed, c, with the propagation of massless particles."

Or for people without a grasp of non-Euclidean geometry:

p is momentum of an entity with respect to an inertial observer

E is the relativistic energy with respect to an inertial observer

v is the velocity of an entity with respect to an inertial observer

c is the speed of light in vacuum

m is the invariant mass of an entity

**v** = **p**c²/E

E² = m²c⁴ + p²c²

"The hyperbolic geometry of space-time naturally associates the invariant speed, c, with the propagation of massless particles."

Or for people without a grasp of non-Euclidean geometry:

p is momentum of an entity with respect to an inertial observer

E is the relativistic energy with respect to an inertial observer

v is the velocity of an entity with respect to an inertial observer

c is the speed of light in vacuum

m is the invariant mass of an entity

E² = m²c⁴ + p²c²

QUOTE (windjammer+Aug 5 2011, 01:00 AM)

You're missing the point. I don't really care if it's two km/s. The point is that it is some velocity and it is that velocity for a reason. No one has a clue what that reason is. And, no one really seems to have much interest in investigating it.

Just a correction (which you may not care about either), we speak of speed of light and not velocity. Velocity of light is anything between -c to +c. Even 2 km per second is fair enough.

Just a correction (which you may not care about either), we speak of speed of light and not velocity. Velocity of light is anything between -c to +c. Even 2 km per second is fair enough.

No, the velocity of light in vacuum is a vector with magnitude c.

So, let me ask the other question more directly. Doesn't it seem a bit beyond coincidence that objects moving away from us, in space, just happen to be 13.8 billion lightyears away in space, which just happens to be the distance that would equate to the age of the universe for something moving at the speed of light? In other words, the expansion rate of the universe equals the speed of light?

Here's another thing about the speed of light that should be considered. There is nothing saying (or, at least, proving) that the speed of light doesn't vary *over time.* The best measure of the speed of light that I can find is 299,792,458 m/s. That means that the speed of light is only measured to +/- 1 meter (or, maybe, according to the miles measurement quoted by rpenner, +/- 100th of an inch). That's not very accurate(+/- 100th of an inch isn't all that close, either, really). So, if the speed of light were to vary over time (e.g. the speed of light were tied to the exansion rate of the universe and the expansion rate of the universe were very slowly changing), then it would be very possible that we couldn't even detect it over the very short period of time that we have been measuring it!

QUOTE (windjammer+Aug 5 2011, 05:33 AM)

So, let me ask the other question more directly. Doesn't it seem a bit beyond coincidence that objects moving away from us, in space, just happen to be 13.8 billion lightyears away in space, which just happens to be the distance that would equate to the age of the universe for something moving at the speed of light? In other words, the expansion rate of the universe equals the speed of light?

No coincidence at all.

13.8 billion light years is as far as we can see because there hasn't been time for light to travel any further.

No coincidence at all.

13.8 billion light years is as far as we can see because there hasn't been time for light to travel any further.

windjammer;

If you think the speed of light has slowed down over time, then you are way behind some others.

http://www.wnd.com/news/article.asp?ARTICLE_ID=39733

If you think the speed of light is increasing over time, then you may be alone in that thinking.

If you think the speed of light has slowed down over time, then you are way behind some others.

http://www.wnd.com/news/article.asp?ARTICLE_ID=39733

If you think the speed of light is increasing over time, then you may be alone in that thinking.

QUOTE (windjammer+Aug 5 2011, 10:33 AM)

So, let me ask the other question more directly. Doesn't it seem a bit beyond coincidence that objects moving away from us, in space, just happen to be 13.8 billion lightyears away in space, which just happens to be the distance that would equate to the age of the universe for something moving at the speed of light? In other words, the expansion rate of the universe equals the speed of light?

a light year is a unit distance. The distance light travels in an Earth year. So, no, it's not a coincidence that those units were chosen. Now you should look up what the co-moving distance is for the observable universe. The co-moving radius of the observable universe is ~ 45.5 billion light years. Light emmitted at the beginning has travelled 45.5 billion light years in 13.7 billion Earth years. You should figure out co-moving distance before you comment.

a light year is a unit distance. The distance light travels in an Earth year. So, no, it's not a coincidence that those units were chosen. Now you should look up what the co-moving distance is for the observable universe. The co-moving radius of the observable universe is ~ 45.5 billion light years. Light emmitted at the beginning has travelled 45.5 billion light years in 13.7 billion Earth years. You should figure out co-moving distance before you comment.

QUOTE (Lasand+Aug 5 2011, 03:01 PM)

windjammer;

If you think the speed of light has slowed down over time, then you are way behind some others.

http://www.wnd.com/news/article.asp?ARTICLE_ID=39733

If you think the speed of light is increasing over time, then you may be alone in that thinking.

The 'some others' are a bunch of fundamentalist creationists. Check the discussion links at the bottom of the article.

If you think the speed of light has slowed down over time, then you are way behind some others.

http://www.wnd.com/news/article.asp?ARTICLE_ID=39733

If you think the speed of light is increasing over time, then you may be alone in that thinking.

The 'some others' are a bunch of fundamentalist creationists. Check the discussion links at the bottom of the article.

Actually, Lasand, I'm not really saying it is speeding up or slowing down. I think the latest concensus seems to be that we are in a closed universe, which would indicate that the universe (and c) were slowing down.

Actually, AlexG, it's not a matter of whether we can see the light, it's the fact that objects move away from us at the speed of light at the distance that coincides with the age of the universe if you divide by lightyears. In other words, that object got 13.8 billion light years distant in 13.8 billion years - the current estimate of the age of the universe. Hence it was moving at the speed of light since the universe began (assuming that c is rather constant over time - Sorry, Lasand, but that is open also. Accelerating, decelerating or staying constant over time is not really the point. That's a whole 'nother discussion, like what happens if the universe were to begin to actually shrink? If light were tied to the expansion rate of the universe, as I am hypothesizing, then all hell would break loose. *Please* don't tie me to the creationist because I used the word "hell").

I'm not interested in this topic enough to stay with it.

A search of a string of key words led to some replies on the same topic that windjammer can read.

http://www.physicsforums.com/showthread.php?t=179662

A search of a string of key words led to some replies on the same topic that windjammer can read.

http://www.physicsforums.com/showthread.php?t=179662

QUOTE (windjammer+Aug 5 2011, 08:10 PM)

Actually, Lasand, I'm not really saying it is speeding up or slowing down. I think the latest concensus seems to be that we are in a closed universe, which would indicate that the universe (and c) were slowing down.

No, WMAP results are a flat spatial geometry just like Guth Inflation predicts. The speed of light isn't slowing down. You're just flapping your jaw so do a little research before you flap on.

No, WMAP results are a flat spatial geometry just like Guth Inflation predicts. The speed of light isn't slowing down. You're just flapping your jaw so do a little research before you flap on.

QUOTE (Lasand+Aug 6 2011, 12:26 AM)

I'm not interested in this topic enough to stay with it.

A search of a string of key words led to some replies on the same topic that windjammer can read.

http://www.physicsforums.com/showthread.php?t=179662

You had the key post on Maxwell but it's to much to ask this guy to research.

A search of a string of key words led to some replies on the same topic that windjammer can read.

http://www.physicsforums.com/showthread.php?t=179662

You had the key post on Maxwell but it's to much to ask this guy to research.

Yep, same windjammer on physicsform and I got the same misunderstanding there, as well. Thanks for the post by tommyburger, though. He and I think somewhat alike. I have looked and looked and **nothing, including Maxwell, even attempts to answer the question** why the speed of light is what it is. The closest I got to someone, at least, admitting the fact was a guy named deesky on physorg.com. So, I'd say it's been fun, but it's actually not. It's been the same as usual. No one really listening but everyone wanting to give an answer. It seems mankind has a deep desire to propound rather than actually think.

The speed of light is what it is because that's what it is.

The reason it has a certain numerical value rather than any other value is simply an artifact of human scaling.

It's value is 299,792,458 metres per second, because of how we define both the meter and the second.

The reason it has a certain numerical value rather than any other value is simply an artifact of human scaling.

It's value is 299,792,458 metres per second, because of how we define both the meter and the second.

Interesting point found in wikipediea searching on Bubble universe theory (got redirected to chaotic inflation. "In 1979 Alan Guth of the United States developed an inflationary model independently, which did offer a mechanism for inflation to begin, the decay of a so-called false vacuum into "bubbles" of "true vacuum" that expanded at the speed of light." So, I think everyone here would agree that the fact that the unverse has been expanding at the speed of light is the effect, not the cause. I won't say I disagree, but I have never seen such a bunch of tail-chasing as when I ask about this topic. I think it is a viable alternative that the speed of light is what it is *because* the universe is expanding at that speed. Thanks for all of the arguing in circles that has done nothing to get nearer to anything that I have seen proposed on multiple sites to saying that there is any reason why the speed of light is the particular speed that it is. I DON'T CARE ABOUT UNITS OF MEASUREMENT! The speed of light is a particular speed that is viewed as a sort of speed limit for objects in this universe. Why is it that particular speed and not some other speed? I say it makes a whole lot of sense that it matches the expansion rate of the universe and the expansion rate of the universe *DEFINED* the speed of light and not vice versa. I have no qualms with someone believing the opposite but please don't try to convince me that you have any evidence to stand on any more than I do! But, please, continue to tell me where I am wrong and where you are so in tune with what is happening and that you have all the answers!

This link explains how “Maxwell discovered a speed equal to the speed of light from a purely theoretical argument based on experimental determinations of forces between currents in wires and forces between electrostatic charges.”

Maxwell's Equations and Electromagnetic Waves

The distance between the earth and the moon are not expanding and the speed of light remains the same.

Maxwell's Equations and Electromagnetic Waves

QUOTE

I think it is a viable alternative that the speed of light is what it is because the universe is expanding at that speed.

The distance between the earth and the moon are not expanding and the speed of light remains the same.

Windjammer has nothing against believe as long as you don't try to force it down his throat. So let me believe the expansion of the universe is limited by the speed of light. Just believing. No hard fact need to prove it. See, the beauty of believing.

My apologies, Boit, poorly worded, I guess. I will be convinced that the speed of light is not tied to the expansion rate of the universe, when someone shows me something to prove otherwise. It just seems like the most likely alternative at this point. As an example of what will not convince me is the fact that someone arrived at the speed of light being what it is based on other parameters of the universe. There is a difference between what is the cause, what is the effect, and just related items that are such because they are related.

I just love that most people can be convinced so easily against of something that hasn't been proven because that is the easy thing to do. In corporate America, it's called, just say no to anything that doesn't currently exist and it is the norm.

I just love that most people can be convinced so easily against of something that hasn't been proven because that is the easy thing to do. In corporate America, it's called, just say no to anything that doesn't currently exist and it is the norm.

Thanks, Nymph. Interesting, but read my post to Boit. Arriving at the speed of light based on other parameters of the universe does nothing to my argument. Of course, those fields are related and, being related, have the potential for indicating characteristics of each other. Great.

You might want to look at Hubble's constant concering the expansion rate of the universe. Distant objects are exanding away from each other. I'm not sure about close objects, such as the moon and earth, I'd have to do more research than I am inclined towards on that subject. But, my guess would be that they are expanding away from each other, due to the expansion of the universe but, in such a fractional manner, that it is hardly measurable - just like the speed of light.

You might want to look at Hubble's constant concering the expansion rate of the universe. Distant objects are exanding away from each other. I'm not sure about close objects, such as the moon and earth, I'd have to do more research than I am inclined towards on that subject. But, my guess would be that they are expanding away from each other, due to the expansion of the universe but, in such a fractional manner, that it is hardly measurable - just like the speed of light.

The universe is not 'expanding at the speed of light'. The expansion rate of the universe is proportional to the distance from the observer. In other words, the further away something is from you, the faster you will observe it to be receeding. This is because space is continually being created between all objects, not because the objects are moving through space. At distances less than that of the local galactic group, gravity is strong enough so that spatial expansion is overcome, and has no effect. The rate of expansion is independent of the speed of light, because it does not consist of movement through space.

"...the universe does expand faster than the speed of light..."

http://curious.astro.cornell.edu/question.php?number=575

windjammer is only considering a Z of 1.4. Here is a Z of 5.

http://apod.nasa.gov/apod/ap981211.html

Some objects seem to be receding from us at a speed faster than the speed of light, indicating an expansion of the universe FASTER than the speed of light.

http://curious.astro.cornell.edu/question.php?number=575

windjammer is only considering a Z of 1.4. Here is a Z of 5.

http://apod.nasa.gov/apod/ap981211.html

Some objects seem to be receding from us at a speed faster than the speed of light, indicating an expansion of the universe FASTER than the speed of light.

Do we have a rate of expansion of space? Yes we have. What's more matter can separate at greater than c without necessarily undergoing a displacement. My believe that c limits matter movement in existing space was right but speed of light does not limit the speed of expansion of the universe, actually the expansion can be greater. Why am I all of a sudden wise? Thanks to Alex, I remember a similar thread that brought these answers. Otherwise check http://en.m.wikipedia.org/wiki/Metric_expansion_of_space

I have a question. Say you have two objects, say the Earth and Moon, in contact, in our expanding space.

What would happen if there were no gravity between them to constrict their motion due to the expansion of space? At what velocity would their separation start, assuming no inertia to overcome?

What would happen if there were no gravity between them to constrict their motion due to the expansion of space? At what velocity would their separation start, assuming no inertia to overcome?

QUOTE (synthsin75+Aug 7 2011, 12:52 PM)

I have a question. Say you have two objects, say the Earth and Moon, in contact, in our expanding space.

What would happen if there were no gravity between them to constrict their motion due to the expansion of space? At what velocity would their separation start, assuming no inertia to overcome?

Ok, I'll take a stab at this.

Let's start with an earth-moon seperation of 384000 km (that's about it's average distance).

Next, the Hubble constant is the rate of spatial expansion. While there is disagreement over it's value, the best current estimate is about 65 Km Per Sec/megaparsec, which is about 20 KPS/million light years.

The earth-moon distance is about 4.05 x 10^-20 percent of a mega light year, so the initial seperation speed due to spatial expansion would be about .81 x 10^-23 Meters Per Sec. (.00000000000000000000081 Km Per Sec. or 0.000000000000000318816 inches per second) (3 ten trillionths of an inch per second) This is many orders of magnitude smaller than the diameter of a proton ( 2 x 10^-14 meters)

If you want to consider the earth-moon in contact, divide by 384000.

Someone check me?

What would happen if there were no gravity between them to constrict their motion due to the expansion of space? At what velocity would their separation start, assuming no inertia to overcome?

Ok, I'll take a stab at this.

Let's start with an earth-moon seperation of 384000 km (that's about it's average distance).

Next, the Hubble constant is the rate of spatial expansion. While there is disagreement over it's value, the best current estimate is about 65 Km Per Sec/megaparsec, which is about 20 KPS/million light years.

The earth-moon distance is about 4.05 x 10^-20 percent of a mega light year, so the initial seperation speed due to spatial expansion would be about .81 x 10^-23 Meters Per Sec. (.00000000000000000000081 Km Per Sec. or 0.000000000000000318816 inches per second) (3 ten trillionths of an inch per second) This is many orders of magnitude smaller than the diameter of a proton ( 2 x 10^-14 meters)

If you want to consider the earth-moon in contact, divide by 384000.

Someone check me?

Alex, is the value of the Hubble constant retarded by gravity's effect on the observations we use to estimate it?

QUOTE (synthsin75+Aug 7 2011, 10:31 PM)

Alex, is the value of the Hubble constant retarded by gravity's effect on the observations we use to estimate it?

The attempts to measure Hubble's constant are done using distant galaxies, well outside local gravitationally bound objects, measuring the red-shift and trying to estimate the distance.

The attempts to measure Hubble's constant are done using distant galaxies, well outside local gravitationally bound objects, measuring the red-shift and trying to estimate the distance.

QUOTE (AlexG+Aug 7 2011, 09:39 PM)

The attempts to measure Hubble's constant are done using distant galaxies, well outside local gravitationally bound objects, measuring the red-shift and trying to estimate the distance.

So yes, but minimally. Thanks.

So yes, but minimally. Thanks.

Unless we're at the centre of the Universe won't there be (on average) as much stuff the other side of what we're looking at as on our side? - so gravity should even out. Until you get close to the edge of the Universe (which is what and where?).

-C2.

-C2.

It doesn't work that way.

We are in the center of the visible universe, since the propagation speed of light and gravity and the age of the universe are both finite. So everyone has the illusion of being at the center of the universe. Expansion gives the illusion that we are at the center of the expansion as well, since it is a uniform expansion of space and not movement through space.

We are in the center of the visible universe, since the propagation speed of light and gravity and the age of the universe are both finite. So everyone has the illusion of being at the center of the universe. Expansion gives the illusion that we are at the center of the expansion as well, since it is a uniform expansion of space and not movement through space.

QUOTE (Confused1+Aug 8 2011, 05:25 AM)

Unless we're at the centre of the Universe won't there be (on average) as much stuff the other side of what we're looking at as on our side? - so gravity should even out. Until you get close to the edge of the Universe (which is what and where?).

-C2.

After all the time you've spent on this site, I'd expect that you'd know there is no center, and there is no edge.

Have you just ignored all posts on the Big Bang and universe expansion?

-C2.

After all the time you've spent on this site, I'd expect that you'd know there is no center, and there is no edge.

Have you just ignored all posts on the Big Bang and universe expansion?

@AlexG,

I see your signature includes "Velocity relative to what?" - I take this as a fair indication that at one time you understood the nature of a rhetorical question - perhaps this coincided with the time when you were 'esteemed' by many. The more recent phase of attacking the individual instead of the question - not so impressive. Please read the (exemplary) reply given by renner - which may (or may not) raise further questions.

Thank you.

-C2.

I see your signature includes "Velocity relative to what?" - I take this as a fair indication that at one time you understood the nature of a rhetorical question - perhaps this coincided with the time when you were 'esteemed' by many. The more recent phase of attacking the individual instead of the question - not so impressive. Please read the (exemplary) reply given by renner - which may (or may not) raise further questions.

Thank you.

-C2.

QUOTE (Confused1+Aug 8 2011, 11:32 AM)

@AlexG,

I see your signature includes "Velocity relative to what?" - I take this as a fair indication that at one time you understood the nature of a rhetorical question - perhaps this coincided with the time when you were 'esteemed' by many. The more recent phase of attacking the individual instead of the question - not so impressive. Please read the (exemplary) reply given by renner - which may (or may not) raise further questions.

Thank you.

-C2.

Your questions did not appear to be rhetorical. If they were, I can't see any reason to ask them.

If they weren't, I'd expected that you'd know better.

I see your signature includes "Velocity relative to what?" - I take this as a fair indication that at one time you understood the nature of a rhetorical question - perhaps this coincided with the time when you were 'esteemed' by many. The more recent phase of attacking the individual instead of the question - not so impressive. Please read the (exemplary) reply given by renner - which may (or may not) raise further questions.

Thank you.

-C2.

Your questions did not appear to be rhetorical. If they were, I can't see any reason to ask them.

If they weren't, I'd expected that you'd know better.

QUOTE (rpenner+)

..

We are in the center of the visible universe, since the propagation speed of light and gravity and the age of the universe are both finite. So everyone has the illusion of being at the center of the universe. Expansion gives the illusion that we are at the center of the expansion as well, since it is a uniform expansion of space and not movement through space.

We are in the center of the visible universe, since the propagation speed of light and gravity and the age of the universe are both finite. So everyone has the illusion of being at the center of the universe. Expansion gives the illusion that we are at the center of the expansion as well, since it is a uniform expansion of space and not movement through space.

QUOTE (Confused1+Aug 8 2011, 08:39 PM)

QUOTE (rpenner+)

..

We are in the center of the visible universe, since the propagation speed of light and gravity and the age of the universe are both finite. So everyone has the illusion of being at the center of the universe. Expansion gives the illusion that we are at the center of the expansion as well, since it is a uniform expansion of space and not movement through space.

This is where I like the balloon analogy. Mark a dot on the surface of the balloon. It is the a center we the sphere. Don't use a disc.

Why is the speed of light "C"? No one knows! You are looking for a mechanical reason and getting a mathematical explanation of measurement. So the question keeps coming up and the answer keeps being the measurement. A rather circular venture into the unknown.

1. A surgeon always sees a surgical solution.

2. A mathematician always sees a math solution.

We need a mechanic!

We are in the center of the visible universe, since the propagation speed of light and gravity and the age of the universe are both finite. So everyone has the illusion of being at the center of the universe. Expansion gives the illusion that we are at the center of the expansion as well, since it is a uniform expansion of space and not movement through space.

This is where I like the balloon analogy. Mark a dot on the surface of the balloon. It is the a center we the sphere. Don't use a disc.

Nice article, AlexG, from Cornell! I guess I give in, once again, and say, once again, that if I really want to pursue this further I need to go get a few degrees.

Ok, okay, okay, last comment. I *still* find it quite interesting that the hubble constant puts things receding from us at the speed of light to be at a distance equivalent to the age of the universe if you divide by the speed of light : 13.8 billion light years! (or, maybe, it's 13.75).

Guys, don't you find it strange that a super-rigid solid, in which transverse waves of light propagate at ~300000 km/s, is ALSO expanding at the same time?

Where the energy necessary to inflate space all around Universe is coming from? Vacuum is imbued with tremendous energy, which gives the light propagating through it its speed. And you're saying, the U is expanding at the rate of the speed of light? WHO/WHAT pumps all the necessary energy into U to support it? Or do you think that space is "cheap" to make?

What evidence do we really have that U is expanding? Only one interpretation of the red shift. But what if there are other interpretations? Why light can't simply "get tired"? Why can't it be stretched/refracted in a funny way while passing through those vast empty bubbles on the peripheries of which the galaxies are supposedly flying apart?

Ain't speed of transverse waves depend on the rigidity of the material they propagate through? There is your answer,**windjammer**

Where the energy necessary to inflate space all around Universe is coming from? Vacuum is imbued with tremendous energy, which gives the light propagating through it its speed. And you're saying, the U is expanding at the rate of the speed of light? WHO/WHAT pumps all the necessary energy into U to support it? Or do you think that space is "cheap" to make?

What evidence do we really have that U is expanding? Only one interpretation of the red shift. But what if there are other interpretations? Why light can't simply "get tired"? Why can't it be stretched/refracted in a funny way while passing through those vast empty bubbles on the peripheries of which the galaxies are supposedly flying apart?

Ain't speed of transverse waves depend on the rigidity of the material they propagate through? There is your answer,

if you think the speed of light has slowed down over time, then you are way behind some others.If you think the speed of light is increasing over time, then you may be alone in that thinking.

Windjammer, that was a great observation and deduction!

The current assumption is not that the universe is expanding but that the objects are moving away from each other.

To assume that the universe is expanding needs a former assumption that the universe is not infinite and has a definite volume. A system which is thought of as infinite cannot expand but rather, the objects within it are said to be simply moving away from each other.

Hope that refines your search just a little bit windjammer.

Btw, I would highly recommend Stephen Hawkin's "A Brief History Of Time" if you have not already read it.

All the best!

To assume that the universe is expanding needs a former assumption that the universe is not infinite and has a definite volume. A system which is thought of as infinite cannot expand but rather, the objects within it are said to be simply moving away from each other.

Hope that refines your search just a little bit windjammer.

Btw, I would highly recommend Stephen Hawkin's "A Brief History Of Time" if you have not already read it.

All the best!

seems to me that if E=MC^2 then we have the reason.

C= sqrt(E/M).

So we now know that C is dependant upon the energy in the universe divided by the mas of the universe.

Pretty straightforward stuff.

So I think we can say the universe is not expanding in terms of it's mass or the energy in it.

C= sqrt(E/M).

So we now know that C is dependant upon the energy in the universe divided by the mas of the universe.

Pretty straightforward stuff.

So I think we can say the universe is not expanding in terms of it's mass or the energy in it.

I read all the replies and questions in the article,and the confusion of windjammer is solved, but one thing is still not clear-

Why c=299792458m/s?

If the photon is really mass less, then why its speed is limited to a constant value? Why it’s unable to cross that particular value?

This is the question due to which I stumbled upon this article.And it is seriously making me confused.

Why c=299792458m/s?

If the photon is really mass less, then why its speed is limited to a constant value? Why it’s unable to cross that particular value?

This is the question due to which I stumbled upon this article.And it is seriously making me confused.

QUOTE (vins15+Mar 9 2014, 08:17 AM)

I read all the replies and questions in the article,and the confusion of windjammer is solved, but one thing is still not clear-

Why c=299792458m/s?

Why c=299792458m/s?

Because it isn't 299792457 m/s and it is not 299792459 m/s. Why is that so? That's just how the universe works. It is a fundamental attribute of a photon (or the hypothetical graviton.) That's why it is called a fundamental constant.

The only time "why" matters is when you find the speed of light to be something other than 299792459 m/s. (Such as when it is traveling through a dense medium.)

Why c=299792458m/s?

Why c=299792458m/s?

Because it isn't 299792457 m/s and it is not 299792459 m/s. Why is that so? That's just how the universe works. It is a fundamental attribute of a photon (or the hypothetical graviton.) That's why it is called a fundamental constant.

The only time "why" matters is when you find the speed of light to be something other than 299792459 m/s. (Such as when it is traveling through a dense medium.)

The answer is that the geometry of space + time is not that of 3D Euclidean geometry [ where (Δx)²+(Δy)²+(Δz)² is length squared, an important quantity] + 1D Euclidean geometry [ where (Δt)² is an important quantity ], but rather (to very close approximation, at least) 4D non-Euclidean geometry where (1/K) (Δt)²−(Δx)²−(Δy)²−(Δz)² is the physically important quantity. K here can be seen here as a conversion factor necessary to make units of time-squared equal to those of length-squared if humans didn't already measure time and length with the same units. Necessarily then, 1/K has units of speed-squared and it has to be something and experiments (all relevant precision experiments since 1859) tell us it is c².

Newton got many things right, but because he lived in a time before modern standards of precision in time keeping. As a result they simplest hypothesis how time, space and motion were related for a free particle were:

**p** = m **v**

and then latter

E = E₀ + ½ m**v**²

and conservation of momentum (**p** ) and energy ( E ) "explained" why particles moved in straight lines when no forces acted on them.

In Einstein's special relativity of 1905, we have the following relationships for a free particle:

**v** = **p**c²/E

E² = m²c⁴ +**p**²c²

which explains more phenomena than Newton's theory.

1) Massless particles can transmit momentum from place to place.

2) Massless particles which carry momentum always move at speed c.

3) E₀, the energy of a particle which is not moving, is proportional to its mass.

4) Newton's formulas are good to many digits of precision for particles that move less than c/100.

Using algebra, we can write (when the magnitude of**v** is less than c):

**v** = **d** c tanh r

where (**d** is a unit vector in a certain direction and r is a number called "rapidity" ). Obviously r = tanh⁻¹ (|**v**|/c).

Then**p** = **d** m c sinh r and E = m c² cosh r and

E² −**p**²c² = m²c⁴ ( cosh r )² − m²c⁴ ( sinh r )² = m²c⁴

This allows us to write:

**p** = **d** m c sinh ( tanh⁻¹ (|**v**|/c) ) = **d** m c [ (|**v**|/c) / √( 1 − **v**²/c²) ] = m **v** / √( 1 − **v**²/c²)

E = m c² cosh ( tanh⁻¹ (|**v**|/c) ) = m c² / √( 1 − **v**²/c²)

And we can see that Einstein approximates Newton when |**v**| < 0.001 c and E₀ = m c² by computing the Taylor series of the above:

**p** = m **v** + m **v** [ (1/2) (**v**²/c²) + (3/8) (**v**⁴/c⁴) + ... ]

E = E₀ + ½ m**v**² + m **v**² [ (3/8) (**v**²/c²) + (5/16) (**v**⁴/c⁴) + ... ]

which requires precision experiments to find a difference between Newton and Einstein.

Newton got many things right, but because he lived in a time before modern standards of precision in time keeping. As a result they simplest hypothesis how time, space and motion were related for a free particle were:

and then latter

E = E₀ + ½ m

and conservation of momentum (

In Einstein's special relativity of 1905, we have the following relationships for a free particle:

E² = m²c⁴ +

which explains more phenomena than Newton's theory.

1) Massless particles can transmit momentum from place to place.

2) Massless particles which carry momentum always move at speed c.

3) E₀, the energy of a particle which is not moving, is proportional to its mass.

4) Newton's formulas are good to many digits of precision for particles that move less than c/100.

Using algebra, we can write (when the magnitude of

where (

Then

E² −

This allows us to write:

E = m c² cosh ( tanh⁻¹ (|

And we can see that Einstein approximates Newton when |

E = E₀ + ½ m

which requires precision experiments to find a difference between Newton and Einstein.

Why is the speed of light "C"? No one knows! You are looking for a mechanical reason and getting a mathematical explanation of measurement. So the question keeps coming up and the answer keeps being the measurement. A rather circular venture into the unknown.

1. A surgeon always sees a surgical solution.

2. A mathematician always sees a math solution.

We need a mechanic!

QUOTE (azo+Mar 10 2014, 04:27 PM)

Why is the speed of light "C"? No one knows! You are looking for a mechanical reason and getting a mathematical explanation of measurement. So the question keeps coming up and the answer keeps being the measurement. A rather circular venture into the unknown.

1. A surgeon always sees a surgical solution.

2. A mathematician always sees a math solution.

We need a mechanic!

...and a crackpot will always look for a crackpot solution. The speed of light is what it is cause that's how fast the fabric of space can adulate.

1. A surgeon always sees a surgical solution.

2. A mathematician always sees a math solution.

We need a mechanic!

...and a crackpot will always look for a crackpot solution. The speed of light is what it is cause that's how fast the fabric of space can adulate.

QUOTE (boit Posted on Today at 6:47 PM+)

The speed of light is what it is cause that's how fast the fabric of space can adulate.

Circular reasoning: The speed of light is caused by adulation and that is how fast it adulates.

How much brain adulation did that take?

Circular reasoning: The speed of light is caused by adulation and that is how fast it adulates.

How much brain adulation did that take?

QUOTE (azo+Mar 10 2014, 11:45 PM)

QUOTE (boit Posted on Today at 6:47 PM+)

The speed of light is what it is cause that's how fast the fabric of space can adulate.

Circular reasoning:

Exactly my point. It is circular cause it is crackpottery (forgive the pun).

Circular reasoning:

Exactly my point. It is circular cause it is crackpottery (forgive the pun).

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