Question Can light travel at a speed less than c?

[James Fairclear]

I
Is red shifted light travelling at a speed less than c?

Light emitted from a light source moving away from an observer at a speed v would intuitively be expected to be travelling at a speed (c – v) but is in fact still measured to be moving at a speed of c. The measurement of speed is based on the time interval between the light being emitted and the light being initially detected at the destination.

The difference between light detected from a stationary source and light detected from a receding source is that the latter is red shifted which means that it is less energetic. But what does that really mean?

Measured over a period of T seconds the light received is quantitatively and qualitatively different from the light that has been transmitted over a period of T seconds.

We can characterise light as a continuous waveform whereby there will be less peaks of the waveform detected per second by a measuring device at the destination than the number of peaks per second detected by a measuring device at the receding light source that is co-moving with the source.

Quantitatively there is less energy per second arriving at the destination from a receding light source than light from a relatively stationary light source.

Energy emitted per second = E
Energy received per second = (E – e)

Eventually the total quantity of energy emitted in T seconds will arrive at the destination but with a portion of that energy (e) delayed by t seconds.

Energy emitted in T seconds = ET
Energy received in T seconds = (E – e) x (T)
Energy received in T + t seconds = ET

Energy from the emitted light will start to arrive at the destination at a point in time T1 commensurate with a speed of c from the receding source. However a quantity of Energy E emitted cannot accurately be said to have arrived at the destination until the same quantity of energy E has been absorbed at the destination at time T2 resulting in (by this definition) an effective speed of light less than c.

As an analogy a locomotive leaves station A and collects one mile of carriages in front of it on its way to station B. The first carriage being pushed by the locomotive may arrive at a station B at 09:00 but the locomotive doesn’t arrive until 09:03.

In conclusion red shifted light from a receding light source can be characterised in terms of the respective rates of energy transmitted and received as travelling at a speed less than c.

 

[Hartmann352]

I'm not sure I agree with Mr. Fairclear as his assumptions seem at first glance to be non-congruent with the cosmological model and Einstein's Second Postulate of Special Relativity*.

The red shift term refers to the human perception of longer wavelengths as red, which is at the section of the visible spectrum with the longest wavelengths. Examples of redshifting are a gamma ray perceived as an X-ray, or initially visible light perceived as radio waves. Just because an electro-magnetic signal is stretched to lower frequency and may take longer to receive does not mean that it is moving any less fast.

The opposite of a redshift is a blueshift, where wavelengths shorten and energy increases. Yet redshift is a more common term and sometimes a blueshift is referred to as negative redshift.

These two paradigms are often compared to both an oncoming and receding train whistle or the electronic siren on an emergency vehicle. As the sound approaches it seems to rise in pitch ( the blueshift) and as it recedes into the distance it falls in pitch (the redshift). The speed of sound doesn't change, but the oncoming sound is bunched together whereas the receding sound is stretched.

There are three main causes of redshifts in astronomy and cosmology:

1. Objects move apart (or closer together) in space. This is an example of the Doppler effect.
2. Space itself is expanding which causes objects to become separated without changing their positions in space. This is known as the cosmological redshift. All sufficiently distant light sources (generally more than a few million light years away) show a redshift corresponding to the rate of increase in their distance from Earth, known as Hubble's Law, after Edwin Hubble.
3. Gravitational redshift is a relativistic effect observed due to strong gravitational fields, which distort space-time and exert a force on light and other particles.

The notion of the universe expanding at a calculable rate was first derived from the general relativity equations in 1922 by Alexander Friedmann. Friedmann published a set of equations, now known as the Friedmann Equations, showing that the universe might expand, and presenting the expansion speed if that were shown to be the case. Then Georges Lamaitre, in a 1927 article, independently derived that the universe might be expanding, observed the proportionality between recessional velocity of and distance to remote bodies, and suggested an estimated value of the proportionality constant, which, when corrected by Edwin Hubble, became known as the Hubble constant. Moreover, two years later, Edwin Hubble confirmed the existence of cosmic expansion and determined a more accurate value for the constant that now bears his name. Hubble inferred the recession velocity of the objects from their redshifts, many of which were earlier measured and related to velocity by Vesto Slipher in 1917. Slipher had measured the first Doppler Shift of a "spiral nebula" (spiral nebula was the obsolete term for spiral galaxies), and soon discovered that almost all such nebulae were receding from Earth.

Though the Hubble constant

is roughly constant in the velocity-distance space at any given moment in time, the Hubble parameter

, which the current Hubble constant, varies with time and experimental exactitude, so the term 'constant' is sometimes thought of as a misnomer.

In the widely accepted cosmological model based on general relativity, redshift is mainly a result of the expansion of space: this means that the farther away a galaxy is from us, the more the space has expanded in the time since the light left that galaxy, so the more the light has been stretched, the more redshifted the light is, hence the faster it appears to be moving away from us. Because it is usually not known how luminous objects are, measuring the redshift is easier than more direct distance measurements, so redshift is sometimes in practice converted to a crude distance measurement using Hubble's law.

We find that, λ = c/ν, where c is constant and invariant, and the speed of light is independent of the relative motion of the source. If the frequency ν is lower, wavelenght λ is greater and you have red shift where the peaks of the light wave are merely stretched out. Thus the speed of light has not changed, only its wavelength.

Please also bear in mind that in 1997, Saul Perlmutter and his team were analyzing their 42 Type Ia supernovae, their selected and preferred standard candle**, thanks to his new use of charged couple devices (CCD's), at redshifts about z~0.5 and finding an odd result: the universe’s expansion was apparently dominated by a cosmological constant, or more generically a “dark energy” pervading all space, which indicated that the cosmological expansion was actually speeding up – which didn’t fit with known models of physics. They announced this startling evidence for a cosmological constant at the American Astronomical Society January 1998 meeting. Because both Perlmutter's team and Brian Rich’s team -including co-Laureate Adam Riess – independently announced matching results at conferences in the beginning of the year, by the end of the year most of the scientific community had accepted these extraordinary findings.

When Perlmutter et al started the project they thought that whatever answer they found would be exciting: if the universe were decelerating ever so slightly because of the small but long term effects of gravity they would know that the universe is finite and will end in a Big Crunch; if not then they could establish that the universe is likely infinite in space and time, and the inflation theory would have a successful prediction. Perlmutter's Team could not have imagined the actual outcome, a surprise that presents a new puzzle to fundamental physics. This is the sort of conclusion to a project that in turn initiates many new projects. Saul Perlmutter et al will now have the fun of trying to figure out what it is that causes the universe to accelerate. Since 1999, (he won the Nobel Prize in Physics in 2011) Perlmutter has been working with his colleagues on many new projects, including the development of a new space telescope that can make a much more precise measurement of the expansion history of the universe and on the frontiers of dark energy.

Still, the velocity of c remains the same, despite the predations of dark energy, out where the redshift is z~0.5.

* Second Postulate of Special Relativity - The speed of light c is a constant, independent of the relative motion of the source.

** Standard candle: a standard candle is a class of astrophysical objects, such as supernovae or variable stars, which have known luminosity, or a known luminosity curve over time, due to some characteristic quality possessed by the entire class of objects. Thus, if an extremely distant object can be identified as a standard candle then the absolute magnitude M (luminosity) of that object is known and can be known to great distances.

Additional reading:

• Hubble, E. P. (1937). The Observational Approach to Cosmology. Clarendon Press. LCCN 38011865.
• Kutner, M. (2003). Astronomy: A Physical Perspective. Cambridge University Press. ISBN 978-0-521-52927-3.
• Liddle, A. R. (2003). An Introduction to Modern Cosmology (2nd ed.). John Wiley & Sons. ISBN 978-0-470-84835-7.
• Freedman, W. L.; Madore, B. F. (2010). "The Hubble Constant". Annual Review of Astronomy and Astrophysics. 48: 673–710. arXiv:1004.1856. Bibcode:2010ARA&A..48..673F. doi:10.1146/annurev-astro-082708-101829.

External Links:
NASA's WMAP - Big Bang Expansion: the Hubble Constant
The Hubble Key Project
The Hubble Diagram Project
Coming to terms with different Hubble Constants (Forbes; 3 May 2019)
Merrifield, Michael (2009). "Hubble Constant"



.

 

[James Fairclear]

I'm not sure I agree with Mr. Fairclear as his assumptions seem at first glance to be non-congruent with the cosmological model and Einstein's Second Postulate of Special Relativity*.

The red shift term refers to the human perception of longer wavelengths as red, which is at the section of the visible spectrum with the longest wavelengths. Examples of redshifting are a gamma ray perceived as an X-ray, or initially visible light perceived as radio waves. Just because an electro-magnetic signal is stretched to lower frequency and may take longer to receive does not mean that it is moving any less fast.

The opposite of a redshift is a blueshift, where wavelengths shorten and energy increases. Yet redshift is a more common term and sometimes a blueshift is referred to as negative redshift.

These two paradigms are often compared to both an oncoming and receding train whistle or the electronic siren on an emergency vehicle. As the sound approaches it seems to rise in pitch ( the blueshift) and as it recedes into the distance it falls in pitch (the redshift). The speed of sound doesn't change, but the oncoming sound is bunched together whereas the receding sound is stretched.

There are three main causes of redshifts in astronomy and cosmology:

1. Objects move apart (or closer together) in space. This is an example of the Doppler effect.
2. Space itself is expanding which causes objects to become separated without changing their positions in space. This is known as the cosmological redshift. All sufficiently distant light sources (generally more than a few million light years away) show a redshift corresponding to the rate of increase in their distance from Earth, known as Hubble's Law, after Edwin Hubble.
3. Gravitational redshift is a relativistic effect observed due to strong gravitational fields, which distort space-time and exert a force on light and other particles.

The notion of the universe expanding at a calculable rate was first derived from the general relativity equations in 1922 by Alexander Friedmann. Friedmann published a set of equations, now known as the Friedmann Equations, showing that the universe might expand, and presenting the expansion speed if that were shown to be the case. Then Georges Lamaitre, in a 1927 article, independently derived that the universe might be expanding, observed the proportionality between recessional velocity of and distance to remote bodies, and suggested an estimated value of the proportionality constant, which, when corrected by Edwin Hubble, became known as the Hubble constant. Moreover, two years later, Edwin Hubble confirmed the existence of cosmic expansion and determined a more accurate value for the constant that now bears his name. Hubble inferred the recession velocity of the objects from their redshifts, many of which were earlier measured and related to velocity by Vesto Slipher in 1917. Slipher had measured the first Doppler Shift of a "spiral nebula" (spiral nebula was the obsolete term for spiral galaxies), and soon discovered that almost all such nebulae were receding from Earth.

Though the Hubble constant

is roughly constant in the velocity-distance space at any given moment in time, the Hubble parameter

, which the current Hubble constant, varies with time and experimental exactitude, so the term 'constant' is sometimes thought of as a misnomer.

In the widely accepted cosmological model based on general relativity, redshift is mainly a result of the expansion of space: this means that the farther away a galaxy is from us, the more the space has expanded in the time since the light left that galaxy, so the more the light has been stretched, the more redshifted the light is, hence the faster it appears to be moving away from us. Because it is usually not known how luminous objects are, measuring the redshift is easier than more direct distance measurements, so redshift is sometimes in practice converted to a crude distance measurement using Hubble's law.

We find that, λ = c/ν, where c is constant and invariant, and the speed of light is independent of the relative motion of the source. If the frequency ν is lower, wavelenght λ is greater and you have red shift where the peaks of the light wave are merely stretched out. Thus the speed of light has not changed, only its wavelength.

Please also bear in mind that in 1997, Saul Perlmutter and his team were analyzing their 42 Type Ia supernovae, their selected and preferred standard candle**, thanks to his new use of charged couple devices (CCD's), at redshifts about z~0.5 and finding an odd result: the universe’s expansion was apparently dominated by a cosmological constant, or more generically a “dark energy” pervading all space, which indicated that the cosmological expansion was actually speeding up – which didn’t fit with known models of physics. They announced this startling evidence for a cosmological constant at the American Astronomical Society January 1998 meeting. Because both Perlmutter's team and Brian Rich’s team -including co-Laureate Adam Riess – independently announced matching results at conferences in the beginning of the year, by the end of the year most of the scientific community had accepted these extraordinary findings.

When Perlmutter et al started the project they thought that whatever answer they found would be exciting: if the universe were decelerating ever so slightly because of the small but long term effects of gravity they would know that the universe is finite and will end in a Big Crunch; if not then they could establish that the universe is likely infinite in space and time, and the inflation theory would have a successful prediction. Perlmutter's Team could not have imagined the actual outcome, a surprise that presents a new puzzle to fundamental physics. This is the sort of conclusion to a project that in turn initiates many new projects. Saul Perlmutter et al will now have the fun of trying to figure out what it is that causes the universe to accelerate. Since 1999, (he won the Nobel Prize in Physics in 2011) Perlmutter has been working with his colleagues on many new projects, including the development of a new space telescope that can make a much more precise measurement of the expansion history of the universe and on the frontiers of dark energy.

Still, the velocity of c remains the same, despite the predations of dark energy, out where the redshift is z~0.5.

* Second Postulate of Special Relativity - The speed of light c is a constant, independent of the relative motion of the source.

** Standard candle: a standard candle is a class of astrophysical objects, such as supernovae or variable stars, which have known luminosity, or a known luminosity curve over time, due to some characteristic quality possessed by the entire class of objects. Thus, if an extremely distant object can be identified as a standard candle then the absolute magnitude M (luminosity) of that object is known and can be known to great distances.

Additional reading:

• Hubble, E. P. (1937). The Observational Approach to Cosmology. Clarendon Press. LCCN 38011865.
• Kutner, M. (2003). Astronomy: A Physical Perspective. Cambridge University Press. ISBN 978-0-521-52927-3.
• Liddle, A. R. (2003). An Introduction to Modern Cosmology (2nd ed.). John Wiley & Sons. ISBN 978-0-470-84835-7.
• Freedman, W. L.; Madore, B. F. (2010). "The Hubble Constant". Annual Review of Astronomy and Astrophysics. 48: 673–710. arXiv:1004.1856. Bibcode:2010ARA&A..48..673F. doi:10.1146/annurev-astro-082708-101829.

External Links:
NASA's WMAP - Big Bang Expansion: the Hubble Constant
The Hubble Key Project
The Hubble Diagram Project
Coming to terms with different Hubble Constants (Forbes; 3 May 2019)
Merrifield, Michael (2009). "Hubble Constant"



.

Thank you for your response.

Since making this point I have realised that my thinking was flawed at least within the context of my specific worked example! I am still thinking about this.

 

[Hayseed]

All the people that think they understand the constant velocity of light, are wrong. Maxwell and Einstein are wrong.

Local time, is a mathematical solution, for a wrongly assumed dynamic.

Maxwell's equations, at best, are close to describing a detected signal, not a propagated signal.

The Doppler effect applies to media waves. The affect is symmetric. In other words, if we put the train whistle at the station, and we are on the train......we will hear the same shift.

But if we try to do that with light.........we get a different affect. The affect of the movement depends on which end is moving. If the emitter is moving, it will affect the detector in a certain fashion. But if the detector is moving, it has a different affect.

This is because light is intermittent. It is NOT continuous and it does not alternate.

Let me draw you a picture of this motion. Draw a dot on some paper. Now draw a radius going east from dot and draw a radius going west from the dot. Make the radii about an inch long. This dot represents the end view of a dipole antenna. The radii represent how far the electric field extends from the antenna. The length of the radii, is set by the excitation duration. With a dipole, that duration is 1/2 period. For instance....if the transmitting frequency is 300MHz.....the WL(wavelength) is 1 meter. 1/2 WL is 1/2 meter long. The period is 3 nano seconds. 1/2 period is 1.5 nano seconds. And during that 1.5 nano seconds that electric radius grows out .5 meters away from antenna. The field will grow at about 1 foot(30cm) for each nanosecond of excitation. Now there are many, many radii around the dot, not just two. At the end of that 1/2 period, and that growth of 1 ft per nano second.......all of those radii are broken and cut. When that happens, all the radii fly out at c. A length, a duration of electrical disturbance is now flying thru space. That length, from the emitter does not change. No matter how fast the emitter is moving, the length of the emitted field does not change. The only thing that changes with emitter movement.......is the time of target impact, not the duration of impact, which comes from the emitted length. So, with the emitter moving, the only thing that changed is the impact timing, or what is called the phase.

We have fixed lengths, like arrows, emitted from a source, no matter the source velocity. When the emitter moves, the distance between source and target changes, causing a different time.....when that length arrives. Emission is instant and point source with location and time.

Absorption is completely different. This is why the relative velocity affect is not reciprocal, like sound or media waves. When that emitted length hits the RX antenna, it will induce a current for 1/2 period. And then, that induced current takes another 1/2 period to relax and react to that inducement. You will detect a full WL duration.

With the absorber movement.......the phase will change, because of a change in distance between antennas.........BUT, the absorber velocity can also change the detection duration, which will change the detected frequency. A frequency change can only be done with absorber movement. Because the frequency.....is the detected duration.

The emission is instant and takes no time. But absorption takes 1/2 period.....and any absorber movement during this time, may affect the detection time.

After the radii are emitted, it takes another 1/2 period to grow anther field to be emitted. During this time, there is nothing being emitted. During the time that the absorber is being relaxed, there is no wave induction.

This is not a complete explanation. There is also a magnetic field, and there is the current mechanics in the emitter and absorber.....in which most do not understand also. Current is greatly mis-understood too.

Media waves have a emission duration, light does not. Only absorption duration.

This is a description of the dynamic.......the mechanics will take further explanation, and you will need an true understanding of current dynamics. But only current mathematics is taught in our schools. This physicality of current is ignored. A fast changing current does not flow down a wire, it spins around the wire. It not only has a axial flow component, it has a radial flow component. We can separate and break the field from a charge.....with a quick flip of the charge.

One can prove what I have said with some electronic lab equipment. Instead of feeding a sine into feedpoint, feed a precision full wave rectified sine into feedpoint. You will see no difference in the received signal.

This should show you that a wave does not alternate, and that it is intermittent. Feed one precision half sine into feedpoint and watch them one at a time at the RXer.

Let's get back to reality.........with science.

The red-shift in starlight is far more likely because of gravity and not velocity. Gravity can change the frequency of oscillation, not because time changes, but because the distance of the oscillation changes. The tic rate of your clock changes, not the rate of time.

We exist in a mechanical universe. No math/information is needed. It's all automatic. No decisions are made. Only life has choice.

 

[Reeii Education]

Yes.
When light is travelling through matter, instead of a vacuum, its speed is slowed by a factor of the index of refraction, n, of the material. So light will travel more slowly though glass, air, water, etc than its vacuum speed, c.