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Old Dec 18th 2017, 09:05 PM   #1
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The speed of gravitational waves

https://physics.aps.org/articles/v10/134


Gravity waves and light move at the same rate, experiment now shows
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Old Dec 18th 2017, 09:50 PM   #2
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"...found that gravitational waves and light from the event arrived at Earth within 2 s of one another. This indicates that the two fundamentally different types of wave travel at the same speed to within 1 part in 1015..."

But why the 2 sec difference ?? article is not clear if this could be a measurement error .

Note also the sloppy use of language , the sensor measured a gamma ray burst ... I don't believe gamma rays are "light" ...article from the maxplank institute too!!

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Old Dec 19th 2017, 02:41 PM   #3
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Originally Posted by oz93666 View Post
"...found that gravitational waves and light from the event arrived at Earth within 2 s of one another. This indicates that the two fundamentally different types of wave travel at the same speed to within 1 part in 1015..."

But why the 2 sec difference ?? article is not clear if this could be a measurement error .

Note also the sloppy use of language , the sensor measured a gamma ray burst ... I don't believe gamma rays are "light" ...article from the maxplank institute too!!
You're mistake is assuming that an astronomical object such as this, i.e. a binary system consisting of two merging neutron stars, is a point body rather than an extended object. E.g. it even takes a few seconds for light to travel the width of our sun. In this case the photons are emitted from each neutron star while the gravitational waves are emitted from the system as a whole. These waves travel 130 million years any difference in speed would mean a large difference in arrival times. The fact that they arrived within 2 seconds implies that they travel at the same speed. It's not possible for speed to be measured exactly, i.e. with infinite precision. As far as not clear if this could be a measurement error goes, its always a given when a measurement is made that the measurement is not given with infinite precision. All physicists and those who really understand physics know that fact and they are the intended audience of those articles.

You're also wrong about how physicists use the term light. In this case they're referring to electromagnetic radiation of any wavelength. Had you ever actually read Einstein's paper on relativity, i.e. On the Electrodynamics of Moving Bodies you'd know that by the term light he was speaking about any and all electromagnetic radiation. His paper is online at:

https://www.fourmilab.ch/etexts/einstein/specrel/www/

In the physics literature any quanta of EM radiation, regardless of wavelength/energy, has the name "photon" attached to it which is also referred to as a quanta of light.

Please stop misinforming readers. Before attempting to "correct" something please exercise due diligence. I.e. I sugggest that you first do a search and/or look it up in a wide range of physics texts before you make such assertions.

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Old Dec 19th 2017, 07:01 PM   #4
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The key point I think is that the merger of two neutron stars is not an instantaneous event, and it is not certain that the stage of the merger that produces the maximum burst of gravitational waves is also the stage that produces the maximum burst of gamma radiation.

Regarding the light verses gamma rays controversy, light and gamma rays are just different colours of electromagnetic radiation, and travel at the same speed.
This speed is almost universally referred to as the speed of light.

I have seen articles that report small discrepancies in the arrival times of different wavelengths of EM radiation from very distant gamma ray blazers.
This was put forward as possible evidence that different wavelengths travel at very slightly different speeds (as has been postulated for certain models of the fine grain structure of space-time)
However I am again inclined to suspect that this effect is similarly due to different wavelengths being produced at different stages of the same event.
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Old Dec 19th 2017, 07:55 PM   #5
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Originally Posted by Woody View Post
Regarding the light verses gamma rays controversy, light and gamma rays are just different colours of electromagnetic radiation, and travel at the same speed.
To be precise they have different wave lengths. Color is a phenomena associated mostly with the human eye and perception and as such cannot meaningfully apply to gamma rays.

Originally Posted by Woody View Post
This speed is almost universally referred to as the speed of light.
Actually its always referred to as the speed of light. "

A good exercise for someone would be to determine whether the known accuracy of the speed of light and the distance that light traveled in the experiment can be used to determine the accuracy of the difference in arrival time of the waves.

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Old Dec 19th 2017, 09:01 PM   #6
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Originally Posted by Pmb View Post
You're also wrong about how physicists use the term light. In this case they're referring to electromagnetic radiation of any wavelength.
Nowhere in any definition I can find , including physics links , is light referred to as electromagnetic radiation of any frequency ... if this were the the case all radio waves would also be classified as "light' ..

Standard definition is ...."Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is visible to the human eye and is responsible for the sense of sight.[1] Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), or 4.00 × 10−7 to 7.00 × 10−7 m..." Wikipedia
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Old Dec 19th 2017, 09:57 PM   #7
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Originally Posted by oz93666 View Post
Nowhere in any definition I can find , including physics links , is light referred to as electromagnetic radiation of any frequency ... if this were the the case all radio waves would also be classified as "light' ..
I thought that you're refuse to read Einstein's paper and as usual I was right. The speed of all EM radiation is defined as the speed of light, and for good reason. I posted that paper so you'd both read and learn. You're simply unable to admit you were wrong and that leads you to drone on and on while refusing to compared.

The problem is that you're the kind of person who doesn't seem to be able to admit to being wrong. You don't look very hard, do you? It took less than a few minutes to find an example.

See: Radioactivity : Photons
[quote]
We group together under the name ‘photon’ a large variety of electromagnetic rays, from radio waves to X-rays and gamma rays, including infrared, visible and ultraviolet light.
...
This diagram shows the same celestial object – the Crab nebula – as seen by different types of photons: infrared, visible light, X-rays and gamma rays. All these photons have the same nature, though their wavelengths (which define the colour in the visible part of the spectrum) and energies are different.
[quote]
Why are you unable to comprehend this simple fact?

You're not a physicist like I am. I've been a physicist for close to 30 years now. Every single day since the early 80's (i.e. when I started college) all I've been doing is studying and working in physics. I've read a great deal more on the subject that you in all likelihood ever have or will. That's why I know (not to be confused with merely believing) that all EM radiation is grouped together under the term "photon."

That includes dozens of textbooks and perhaps hundreds of articles. You're simply too ignorant on the subject as well as unwilling to learn or admit that you're wrong. You're so darn caught up in semantics that you always miss these kinds of points.

There are extremely good reasons to refer to all EM radiation of any wavelength as light. All EM radiation consists of photons and a photon is [i[defined[/i] as a quantum of light. The frequency of light depends on ones frame of reference and there's no valid reason to say that what an object is depends on its frame of reference. Light in one frame can legitimately be called light in another frame. A gamma ray photon in one frame is a blue photon in another.

Originally Posted by oz93666 View Post
Standard definition is
Standard definitions are what laymen use, not physicists. E.g. if you look up the term "mass" in almost any dictionary you'll find it defined quite different than its defined by physicists. Many books define mass as "quantity of matter
" which will never be found in any physics text.

I was right to put you in my ignore file. I'll eventually learn not to bother correcting you because you'll never understand since you never have in the past. No matter what physicists say or do you claim they're all wrong because they're "not as sensible" as you are.

Back into my ignore list you go.
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Old Dec 20th 2017, 09:26 AM   #8
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As in all fields, Physicists use some terms slightly differently from their everyday common use.

Yes, in common parlance, light is just that tiny fraction of the electromagnetic spectrum that humans can see.
Some animals (e.g bees) can see a short way into the ultraviolet, Rattle snakes can "see" into the infra-red (though not with their eyes, they have special infra-red sensitive organs in pits on their noses).

Using technology we can now detect radio-waves, micro-waves, X-rays, Gamma-Rays etc.
However these are all just different flavours, of the same type of phenomena (Electro-Magnetic Radiation).
The division of Electro-Magnetic Radiation into these different regions is quite artificial and is largely based on the history of the development of the technology used to detect and/or generate them.

Electro-Magnetic Radiation is a bit of a mouthful (I am copying and pasting rather than re-typing it each time) so Physicists often just say "light" and understand (from the context) that this should be taken to apply to the whole electro-magnetic spectrum.

Note that I used "colour" in a previous post, and "flavour" in this post, I am just trying to denote different varieties of the same thing, without using using the technical terms frequency and wavelength.
EM Radiation definitely does not have a taste, and as Pmb says, it really only has colour (or color for our American readers) in the (very) narrow band we can see.
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Old Dec 20th 2017, 12:40 PM   #9
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Originally Posted by Woody View Post
As in all fields, Physicists use some terms slightly differently from their everyday common use.
Yeah, but I told him that right off the bat and he ignored it. I even showed him Einstein's paper on SR as a solid example and he ignored that too. sigh!

By the way. The same also applies to math as well in certain cases in physics. E.g. in some texts a scalar is defined simply as a number whereas in tensor calculus its defined as a number which remains invariant upon a change in coordinates.

Originally Posted by Woody View Post
Yes, in common parlance, light is just that tiny fraction of the electromagnetic spectrum that humans can see.
Which is always frame dependent. So what is "light" in one frame is a gamma ray in another and IR in yet another. In all inertial frames the speed is always the same, c.

Originally Posted by Woody View Post
However these are all just different flavours, of the same type of phenomena (Electro-Magnetic Radiation).
The division of Electro-Magnetic Radiation into these different regions is quite artificial and is largely based on the history of the development of the technology used to detect and/or generate them....
Exactly! I all cases I know of, when a text book author calculates the speed of an EM wave they always refer to it as the speed of light. Namely because that's exactly what it is.

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Old Dec 20th 2017, 09:46 PM   #10
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Originally Posted by Woody View Post
Electro-Magnetic Radiation is a bit of a mouthful (I am copying and pasting rather than re-typing it each time) so Physicists often just say "light" and understand (from the context) that this should be taken to apply to the whole electro-magnetic spectrum..
Well in that case you should have no trouble supplying just ONE link from a search such as "light meaning in physics" ...

Because I can supply a thousand physics definitions and meanings for this word that say it's a PART of the EMS.
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