Speed of Light

You are correct but that is why we use the +/- symbol to headge our numbers. Oh and those Astro-physics dudes can prove anything with those equations.

Ow! Ow, ow ow ow!!!

I am not even gonna touch this one.

But, nice.

-e

Light doesn't bend around massive objects - space does. Or something like that.

What exactly is space ???

Space is what was here before we were. I would like to know what meaning time had before we decided that it took a year for our planet to orbit our sun? And how many billions of our "Light Years" passed before our universe existed?

Time cannot be perceived without intelligence to measure it. It's there just like the sound waves when trees falls in the forest with no ears to hear them. Our Universe is presently projected by NASA from satellite data (WMAP) to be around 13.7 Billion Earth years old. It's flat in shape and made of 73% dark energy 23% dark matter and 4% baryonic matter (Atoms). They also project that there are at least 250 Billion galaxies in our universe. Before our universe existed nobody knows anything about what could have occupied it's space.

Interesting. On a philosophical note, if our Universe is finite, and expanding, WHAT is it expanding into? Is space being created as the Universe expands? And if we are seeing "echos" of the Big Bang in low temperature radiation permeating the Universe, doesn't this imply a surrounding membrane from which the radiation is "echoing"? Otherwise, wouldn't the radiation have long ago exited our neighborhood in the Universe and dissipated into the far reaches of "space"? Or is the Universe a closed entity, and the radiation just keeps circulating and permeating all space (which returns to the "enclosing membrane" question) and "cooling" with time? What is the interaction, if any, between the "echoing" background radiation and Dark Matter, which may be the major "physical" component of the Universe?

Space doesn't have an outside, as does a balloon or an egg. Consequently, it has no "membrane" or boundary which serves to separate the outside from the inside. As the terms outside, boundary, and inside exist only in relation to each other, the Universe has no inside, either. Kinda strange, but there you are. Think of it this way: if space has an enclosing "membrane" separating it from something else, wouldn't that Something Else also be part of the Universe? If not, why not? The distinction between Universe and Non-Universe would be an arbitrary one, assigned at the "membrane" by those who believe it to be so in the same way that someone might arbitrarily - and foolishly - designate the interior of a balloon to be the extent of space. The Universe, as an "object," has a very different nature than that of an ordinary volume such as a balloon. There is no Outside, and no Membrane separating the Outside from the inside, what we call The Universe. If there were, these would also be part of All That Is, yes?

-e

It's only Wednesday and this blog is already so heavily deviated. This sounds more like a Friday evening bartender discussion. (Or was it Saturday morning, Time was cheating on me)

How the hell did they knew that they had to note down BC on those pyramids?

You have to sift through the fun posts to get to the puckered ones. Happens even in bars.

Who Cares ???

Space is just a reference system. So it's an abstract notion in our minds, not something that "exists". Matter "exists", not space. Space is just the imaginary grid that we use to measure matter.

u23 writes: "Space is just the imaginary grid that we use to measure matter."

-----

My car has no imagination whatsoever. Yet, I have to put real gas in it so it'll go from one imaginary place to another. Go figure.

-e

meh.

What if we are just the musings of a super-being's brain?

And, in turn, our musings believe that they are really alive within the landscape of our inner being. A rather more chaotic place than where our lives unfold...

meh, and we're gone... Poof!!!

Morpheus: I imagine that right now you're feeling a bit like Alice. Tumbling down the rabbit hole?

Vermin: You could say that.

Morpheus: I can see it in your eyes. You have the look of a man who accepts what he sees because he's expecting to wake up. Ironically, this is not far from the truth. Do you believe in fate, Vermin?

Vermin: No.

Morpheus: Why not?

Vermin: 'Cause I don't like the idea that I'm not in control of my life.

Morpheus: I know exactly what you mean. Let me tell you why you're here. You're here because you know something. What you know, you can't explain. But you feel it. You felt it your entire life. That there's something wrong with the world. You don't know what it is, but it's there. Like a splinter in your mind -- driving you mad. It is this feeling that has brought you to me. Do you know what I'm talking about?

Vermin: Wal Mart?

Morpheus: Do you want to know what it is?

(Vermin nods his head.)

Morpheus: Wal Mart is everywhere, it is all around us. Even now, in this very room. You can see it when you look out your window, or when you turn on your television. You can feel it when you go to work, or when go to church or when you pay your taxes. It is the world that has been pulled over your eyes to blind you from the truth.

Vermin: What truth?

Morpheus: That you are a slave, Vermin. Like everyone else, you were born into bondage, born inside a prison that you cannot smell, taste, or touch. A prison for your mind.

(long pause, sighs) Unfortunately, no one can be told what Wal Mart is. You have to see it for yourself. This is your last chance. After this, there is no turning back.

(In his left hand, Morpheus shows a blue pill.)

Morpheus: You take the blue pill and the story ends. You wake in your bed and believe whatever you want to believe.

(a red pill is in his other hand)

Morpheus: You take the red pill and you stay in Wonderland and I show you how deep the rabbit-hole goes.

(Long pause; Vermin reaches for the red pill)

Morpheus: Remember -- all I am offering is the truth, nothing more.

Vermin: Let's go shopping, then!

Morpheus: Right. I'll drive.

-e

Obviously you've never seen the South Park Wal Mart episode!!!

Isn't that the episode where everybody is played by Hugo Weaving?

-e

Sort of... It's where the find the true heart of Wal Mart and smach it. But it really doesn't matter.

So why did "Agent Smith" turn up in "Lord of the Rings"?

He needed the "lolly."

Those Agents can turn up anywhere. Instead of taking over the avatar of some subway drunk in order to fight Neo, Smith took over Elrond's avatar. Any harm in wanting to be half-elven and take some R&R at the Last Homely House? Even bad guys need vacations! Not only that, he was paid handsomely for this stint. Almost makes you wanna be an agent. (In my case I sure as hell wouldn't wanna be Princess Arwen's >dad<. Oh behaaaaave! :-)

...bad guys need vacations...

It was just a gig, man

"gig" in Hebrew - "Khaltoora"

That's what they >want< you to think! Here, take this Blue Pill, Alice. - Cheshire Cat :-)

Very cool, tho I sent my mind, postage due, on to Uranus. String Theory

Oh, you're not going to start that again, are you?!

See other thread on "What is Space?"

Who the hell started that thread, anyway?! That's what I'd like to know.

-e

What exactly is space ???

its what ur taking up.

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

Speed of light in a vacuum is absolute. It does not vary.

Prove IT !!!

DONE!!! Happy now?

Your assumption is really wrong; and was/is one of Einstein's great triumphs! The speed of light moving past an object (especially massive) traces a path through space, which is bent (Yes, space is bent) around the object. Einstein says that gravity is the bending of space-time about an object, the larger the mass the more the bending. Also, remember that this bending is in 3-dimensions, which is kind of hard to imagine.

The speed of light is still c, but it's actually taking a longer path through the bent space. This was pretty much proved by two experiments - one traced the path of light from a star that was bent around the Sun because of its gravitational field, the other experiment correctly predicted the orbital period of Mercury around the Sun; there was a few second discrepancy that astrophysicists were trying to account for since the days of Newton. Einstein's gravitational equations nailed it!!!

"Also, remember that this bending is in 3-dimensions, which is kind of hard to imagine. No, it isn't. The bending he refers to is the bending of 4 dimensional space/time, not 3 dimensional space. The equations that are used to discribe the bendings of 4D space are equivalent to equations that discribe the motion or flowing of 3D space. Gravity cause the path of a beam of light to 'bend' because the space it is moving throw is moving perpendicularly to the path of the light.

Point taken.

The light follows a geodesic, the shortest distance between two points in curved, four-dimensional spacetime. Light speeds along this geodesic at a constant speed. It's not that the light is taking a shorter or longer route and therefore must alter its speed to accommodate this new path. The light is taking the shortest route all along, and its speed is constant - the speed of light.

-e

That works, too.

Hi -e, you wrote: "It's not that the light is taking a shorter or longer route and therefore must alter its speed to accommodate this new path."

I think this issue is a bit confusing, due to the Shapiro time delay of light. Irvin Shapiro (et. al.) bounced radar signals off Mercury, Venus and Mars when they were near and at superior conjunction (i.e., more or less behind the Sun) and timed the return signal. For Mars, there was a predictable 250 μs delay in the 42 minute round trip of light.

This can be interpreted that in our (Earth) reference frame, light "slowed down" when it passed the Sun at close range. However, if we could put momentarily stationary observers all the way along the path of the light beam, they would not have detected a deviation in the speed of that light beam in their local inertial frames. Hence, it cannot be called the "slowing down of light", but is rather named the "time delay of light".

Fore clarity, as you probably know, the delay is not caused by the bending of the light beam. It has do with the slowing of clocks (gravitational time dilation) and the contraction of space due to space-time curvature in the vicinity of the Sun, each contributing half of the effect.

Regards, Jorrie

Yes, I neglected that. Thanks.

-e

No. It actully has to go through a bent path (AKA longer) through space. The time effect is wraped up with that.

Hi vermin, you wrote: "No. It actully has to go through a bent path (AKA longer) through space. The time effect is wraped up with that."

If you're referring to the time delay, then you're wrong here. The best explanation I've ever seen is contained in Clifford Will's "Was Einstein Right", but I'm sure there are good one's on the web somewhere...

The bent path makes very little difference to the time delay. It is contraction of spacetime near the Sun that makes up the bulk of the 250 μs observed light delay. If you could bounce a radar signal off a neutron star (with nothing along the way), there would be no bent path through space, but still Shapiro time delay.

Regards, Jorrie

Hi vermin, me again with "second thoughts".

If you meant by "bent path" the effect illustrated with the imaginary "dent in space" around a massive object, you may be halfway right! This corresponds to the contraction or curvature of space, which produces half of the time delay. The other half is time dilation.

The best analogy of Shapiro time delay that I've heard is that near a massive object, "light takes shorter steps and it takes them at a slower rate" when compared to our local experience.

Regards, Jorrie

Jorrie and Vermin, from light's standpoint, if you will, space is not 'bent' at all because such curvature would represent a detour, a higher-energy path different from the minimum-energy path light actually takes. The curvature is evident only from an "outside" perspective, so to speak. Think of the ant-on-the-apple analogy in Misner, Thorne and Wheeler's book "Gravitation." The ant is aware of no curvature at all. We are aware of the curvature only because we're looking at the apple from a different perspective.

Looking at this analagously from another angle (pun intended), the graph of a logarithm on a piece of log paper is a straight line.

-e

What about black holes though? A ball of matter with the density of a star at 1/millionth the size. Our scientific evidence supports the fact that space/time is alter dramatically around this object and that light itself cannot escape it's gravitational pull. In my opinion, space is a 3-Dimensional grid where light emitted from a star travels straight in all directions unless blocked and absorbed by a passing object (assuming a slight bending of path around the edges due to an atmosphere maybe), or completed consumed by a black hole because the grid the light was traveling on was altered around it like a drain.

My opinions might be wrong, I'm not an expert. Then again, maybe it's just our lack of understanding of black holes since they tend to defy most of the laws and concepts we have about physics and reality.

Most of your post is conceptually correct, actually, so you're pretty close the mark. Light travels in "straight" lines in "flat," four-dimensional spacetime (yes, I know the nomenclature sounds a bit weird. Blame it on the limits of human language). Perhaps an analogy is in order: picture galaxies, stars, planets, black holes - stuff - all sitting on an ordinary, everyday rubber membrane. The more massive objects are going to make deep dimples. Black holes make an infinitely deep "dimple" in our sheet, and anything going straight in (I'm deliberately ignoring here the effects of frame-dragging around rotating masses, in which things don't go in straight) never come back out. Overall this rubber sheet is not flat, and so a marble rolled across this sheet will veer one way, then another as it encounters the various dimples. Where the marble is far from other objects, it will roll in a straight line. Where it is near other objects - provided it doesn't run into them directly - it will follow the path of least resistance and veer this way and that. To an observer, the marble's trajectory will curve. To the marble, which sees only its immediate location and cannot see anything of the membrane at all, it is traveling in a straight line.

-e

Hey! I had rubber sheets when I was a little kid!!!

I'm quitting this thread. I have an Excedrin Headache!!!

I understand what you're saying, but remember what Einstein pointed out himself: When one measures time, one has to use some sort of device that is subject to spatial contraction. And visa versa, to measure a distance, one has to rely on something that references time...

Around and around we go! Weeeeeeeeee!!!

Its not faith but curiosity that makes good science. Prof Barnhart

Imagination is more Important then Knowledge-- Albert Einstein

I don't want knowledge, I want certainty! -- David Bowie

Just imagine you have certainty.

Dear Jorie,

We are calculating distances in space based on speed of light or Red shift of light. Is this time dilation not affecting red shift. Is Red shift not dependent on time dilation.

Dear Jorrie,

We calculate time required for light to reach mars and come back based on the clock on Earth. Sameway time required for travel of light from distant Galaxy is counted on time based on the clock on Earth. During this travel light is passing through space time of different degrees of contractions. Even though speed of light C is constant in its own frame it is varying for the observer on earth(c'). Spatial distances are measured with respect to Earth-time of light travel. Measurement of light travel time on earth is dependent on amount of space travel contractions encountered by light during travel.

My question is if our calculations of spatial distances are correct?

Light travelling in the vicinity of black hole will exhibit very high time delation and on clock on Earth time taken for its travel is very long. If we multiply this time by c the distance of blck hole will be much more than what actually is.

Hence my next question is if the Universe is really so big or it our miscalculation.

Nandan

Hi nandan, you asked: "My question is if our calculations of spatial distances are correct?"

One thing that you must remember is that we do not measure astronomical distances by timing light! We have nobody at the star, or whatever, to start a stopwatch! We only express distances in terms of how long it would take light (in free space, speed c) to cover the distance and call it light-years.

The real distance yardsticks are parallax measurements for nearer objects, proper motion for medium distance and Cepheid variable stars combined with supernovae for long range measurements. None has anything (directly) to do with the speed of light. These yardsticks are then used to calibrate the distance-redshift relationship and the redshift is then used for extreme ranges.

Redshift is also not dependent upon the speed of light somewhere in-between, i.e., light passing a massive object does not influence the redshift of a distant galaxy as we measure it here on Earth.

In fact, astronomers (professionally) don't even speak of light-years. They speak parsecs, directly derived from parallax: a parsec is the distance at which the peak parallax caused by Earth's motion around the Sun equals one arcsecond, about 3.26 light-years.

Regards, Jorrie

E=MC^{2 ???}

Guest wrote: "E=MC^{2 ???}"

What are you actually asking?

Jorrie

From what I can tell, in Guest's equation C is raised to the power of 2 and three question marks. This may be an obscure reference to Dark Energy. Or it may be Guest's attempt to relate Dark Energy and Dark Matter in an interrogative equivalence relation. Einstein himself applied this technique with varying success.

-e

How is it related to "Heisenberg's Uncertainty Principle"; for example, is this "Guest's Uncertainty Principle^??"

I'm not really certain!

Prove It !!!

Might you be the same two-word lurker from Post #42? It's okay to have a real dialog on this forum, btw. Can you come out from behind your keyboard?

-e

I feel that light when passing through space time contraction will cause Red Shift. Red shift is caused by the delay in the arrival of subsequent waves of light at the place of observer. Isn't it so?

Nandan

Hi nandan, you asked: "Red shift is caused by the delay in the arrival of subsequent waves of light at the place of observer. Isn't it so?"

Yea, in a way, but it's far better to think of redshift as simply an increase in the wavelength of the transmitted light (or a decrease in frequency, if you like). Now, as a passing light ray approaches a massive object, the wavelength is blue-shifted and after it has passed the object, the wavelength is red-shifted by the same amount - hence, no net wavelength change caused by the massive object!

Cosmological redshifts have all to do with the expansion of space - in the process the wavelength of photons get stretched more and more the longer they travel.

Does this make sense? Feel free to ask for more detail if you are still unsure.

Regards, Jorrie

Jorrie,

Redshift is used to measure the distance of objects in space.

OK but you relate that the more redshift, the further away the object is.

To my knowledge, every galaxy in space is moving apart from each other, with one central point: where the big bang happened, making that those at the outside are the fastest and those at the other side from our point of view have the highest relative speed (for us) as they move away from us, the more redshift it results in.

In fact we only measure the speed in this way. Other methods show us the position and the speed position combination shows that indeed there is a central point in our system from where it all started. The figures match that nice that it was possible to pinpoint a date.

Am I right and did you shortcut a bit?

Regards,

Gwen

No, this is wrong.

Not all galaxies are moving away from each other. In fact, we're due to collide with Andromeda in about a billion years. They're all moving all over the place. Furthermore, we've detected a bunch of galaxies (ours included) moving like a river toward something called the "Great Attractor." Nobody knows what it is.

It gets worse... The Universe is really expanding. Space is actually getting bigger. That's why there is no point where the big bang happened. The big bang created space, time, and all the matter and energy within. As a result, no matter where you are in the Universe, your location appears as the center of spatial expansion. It's this expansion of space that causes the Hubble Shift, which is responsible for the red shift that we use to measure really far distances.

Other than that, we use the Doppler red shift to tell if something is moving towards us or away from us. For example, if a star in our galaxy is moving towards us, its light is shifted toward the blue and if moving away its light is shifted toward the red.

So there are two red shifts?

Do you have some reading info on this?

Is this new info that my teachers 20y ago could not have known?

Or did I skip the wrong class?

Gwen

There's the red shift due to the expansion of space itself. Suppose that six billion years ago a photon is emitted from some very distant supernova and is eventually observed on Earth. In the intervening six billion years between the photon's emission and subsequent observation, space itself has expanded, including the volume of space through which the photon has traveled all these years. By the time the photon arrives at the instrument, it has been "stretched" by the same amount as the space it has traversed has expanded. Its wavelength is now longer, making it redder. The more distance it traverses, the longer it is in transit, the more it is stretched along with space itself, and the redder it becomes.

-e

Hi Gwen, Europium and Vermin have covered your question well, except maybe this one: "So there are two red shifts?"

Yes, there are: a cosmological redshift and a normal Doppler redshift in the case of a galaxy that moves away from us through space (part of the galaxy's so-called peculiar movement).

In fact, if we look at galaxies closer than about 200 million light-years, the peculiar movement may be of the same order of magnitude than the cosmological redshift and we cannot use the redshift directly to determine distance. Other, non-redshift methods are used for the shorter range. This is because the cosmological redshift needs large distances to become significant.

Regards, Jorrie

Nobody has mentioned the Night Shift. Now what the heck is that?

It is said that Nitrate is 1.5 x Dayrate. Will that do?

Give me a moment while I shift this here Paradigm. :-)

Gwen writes: "every galaxy in space is moving apart from each other, with one central point: where the big bang happened..."

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Actually, Gwen, there is no "central" point, as, in a manner of speaking, the entire Universe is that "point." Perhaps one analogy might be to consider the surface of a balloon and dots drawn on it. If you inflate the balloon the surface area increases, forcing the dots to move farther apart from each other. Dots farther from a given dot (following the surface) will move away faster than nearer dots, but it doesn't matter which dot you choose. They'll all be moving away from that choice of dot the same as they would from any other choice.

-e

thats not a very good proof

That's not a proper proof! It doesn't give me confidence!

Actually, E Man is making the point that each dot on the balloon sees itself as the origin of expansion. Since the big bang (if you choose to believe) not only created mass and energy, but also space and time, as space/time expands, in 3 or 4 dimensions, all points in space seem to see themselves as the original point of expansion.

I see your point.

It's not a proof at all and never was intended as such. It is an >analogy< meant for purposes of illustration only. If you want 'proof' there's enough information at your Internet fingertips to fill the Library of Congress. -e

Let me ask you a question: What's the speed of dark?

-e

From Dali's surrealist joke book...

Q: "Why did the chicken cross the road?"

A: "Fish."

You could not be more wrong if you tried.

Founding axiom of Relativity is that "the speed of light is constant in all frames of reference"

This is the the reason why space-time 'bend' around heavy objects and why when running quickly you can get a 5 metre pole into a garage 3 metres long before the pole breaks.

Suggest that you start back at Special Relativity 101!

Its all Academic

It wasn't that long ago that the sound barrier was a absolute.

Its all Academic

No it isn't. Some of it's an argument.

Ow! Stop hitting me on the head! I came in here for an argument!

I'm sorry, but I'm not allowed to argue with you until you've paid.
-e

Er, is that the five-minute argument, or the full half-hour?

(With apologies to the Monty Python team.)

I don't know. I might be arguing on my spare time.

Yes, you do and no, you're not.

Are you sure

I'm not allowed to argue with you until you've paid, too. I have a living to make!

-e

Nice. Friendly, too.

Could you please log in, there are to much guests in this discussion.

And they respond by the speed of light.

Its all Relative

Hi nandan. You are right, the speed of light depends on the medium which it is travelling through. When light travels from a less dense medium to a dense medium it slows down, ie, from air into a diamond. But when the light exits the diamond it speeds up again to the speed of light through the air. This give rise to the phenomonen known as refraction, and every transparent medium has a different index of refraction. This is used by gemmologists to help with the identification of gemstones, likewise by mineralogists to identify a given mineral species. The refractive index of diamond is, 2.417, thus light travelling through a diamond is 124,000km per seconed while light travelling through atmospheric air is 300,000km per second. The refractive index of quartz is, 1.55, thus light travelling through quartz is 193,550km per second. Spencer.

Also, remember that as light passes through an object, particles can potentially travel faster than light through the object. When this happens, an electromagnetic shock wave (like a sonic boom) is created which creates a blue flash. This flash is known as Cerenkov Radiation.

Vermin writes: "When this happens, an electromagnetic shock wave (like a sonic boom) is created which creates a blue flash. This flash is known as Cerenkov Radiation."

-----

What is your comment?

The pic is in illustration of vermin's previous post where he mentions Cerenkov radiation. In the pic neutrons are zipping through the water surrounding a reactor core (running at full power) at a speed faster than the speed of light in water, producing the characteristic blue glow of Cerenkov radiation. After they dump their energy in this way, they slow down and behave themselves.

-e