[Kryptid]

Light travels at a constant velocity in a vacuum. Constant velocity doesn't involve a force.

[Michael Sally (OP)]

Light travels at a constant velocity in a vacuum. Constant velocity doesn't involve a force.

Light travels at a constant velocity  in a vacuum because of ?

Lights velocity is ?  Velocity being speed and direction .

Light requires a force to pass through glass and light requires a force to accelerate on exiting the glass .  How can you say a force isn't required when the physics involved requires a force ?

[Janus]

requires no force to continue on its way, per Newton's first law (which is admittedly more applicable to the rock than to light).

How do you explain light's acceleration when exiting a medium if there is no force involved ?

The problem here is that you trying to apply the same rules to light that you would apply to a massive object like a baseball.
But you can't because they are not the same type of thing.  To accelerate a baseball, you do have to apply a force to it, because a baseball has something called "proper" mass.  Light has no proper mass, and the rules that govern such things require that they have to travel at c in a vacuum. When light leaves a medium, it just begins to move at c naturally as it is required to.
The reason it take a force in order to accelerate a ball is because you need to change its kinetic energy.  So if a ball travels through something that reduces it speed it give up energy, and that energy has to be replaced to speed it up again.
The energy of light however is tied to its wavelength, the shorter the wavelength, the more energetic.
When light enters a medium it not only slows down, but it shortens its wavelength, the shortening of the wavelength offsets the lowering of speed.  When it exits, if speeds up and lengthens its wavelength.   Basically the light slows down in the medium without giving up energy, so nothing has to replace lost energy for it to speed back up again when it leaves.
Similarly, if you toss a baseball up into the air, it will lose KE as it climbs against gravity and slow down.
Light also loses energy climbing against gravity, but instead of slowing down, it lengthens it wavelength while continuing to travel at the same speed. (This is called gravitational red-shift because red light has the longest wavelength in the visible light spectrum.)

[Michael Sally (OP)]

Sorry for posting again before I received a reply but I thought it would help us all think about the question and physics involved if I drew a diagram of light passing through glass.


c-model.jpg (21 kB . 816x460 - viewed 2424 times)

On the diagram I have also added a force tag F which may or may not be the cause of lights speed . This is to be determined in discussion before any theoretical build , otherwise any presentation would just be speculation .

[Michael Sally (OP)]

requires no force to continue on its way, per Newton's first law (which is admittedly more applicable to the rock than to light).

How do you explain light's acceleration when exiting a medium if there is no force involved ?

The problem here is that you trying to apply the same rules to light that you would apply to a massive object like a baseball.
But you can't because they are not the same type of thing.  To accelerate a baseball, you do have to apply a force to it, because a baseball has something called "proper" mass.  Light has no proper mass, and the rules that govern such things require that they have to travel at c in a vacuum. When light leaves a medium, it just begins to move at c naturally as it is required to.
The reason it take a force in order to accelerate a ball is because you need to change its kinetic energy.  So if a ball travels through something that reduces it speed it give up energy, and that energy has to be replaced to speed it up again.
The energy of light however is tied to its wavelength, the shorter the wavelength, the more energetic.
When light enters a medium it not only slows down, but it shortens its wavelength, the shortening of the wavelength offsets the lowering of speed.  When it exits, if speeds up and lengthens its wavelength.   Basically the light slows down in the medium without giving up energy, so nothing has to replace lost energy for it to speed back up again when it leaves.
Similarly, if you toss a baseball up into the air, it will lose KE as it climbs against gravity and slow down.
Light also loses energy climbing against gravity, but instead of slowing down, it lengthens it wavelength while continuing to travel at the same speed. (This is called gravitational red-shift because red light has the longest wavelength in the visible light spectrum.)

Sorry I was posting as you made your post .

You say that when light exits a medium it naturally  speeds back up  to c . For anything to speed up it would require an ''engine'' , internal or external . 

A medium slows down light ! What of the medium slows down the light ?

Is it density or some sort of resistance force ?

For light to slow down in a medium the physics would require an opposing force .  If there was no ''engine'' involved , when the light exited the medium , the light  would retain the speed it had whilst  passing through the medium .

As Newton stated a body in motion will remain in motion unless acted upon by external forces .

Light cannot slow down passing through a medium then speed backup again without some form of force being involved .

Sorry I do not believe in magic .

[evan_au]

Is the speed of a light a consequence of ?

Maxwell's equations predicted the possibility of electromagnetic waves.
- Radio waves were discovered soon after, by Hertz and others
- It was also realized that visible light travelled at this speed too, so light must also be an electromagnetic wave

Maxwell's equations imply a speed of light in any material of 1/√(εμ), where:
- ε is the permittivity to electric fields in that material
- μ is the permeability to magnetic fields in that material
- ε and μ can be measured in the laboratory (in that material)
- This equation has some similarities to the equation for the speed of a sound wave in a guitar string.

So when electromagnetic waves (eg light) pass from one medium to another, the values of ε & μ change, and so the speed of light changes.
- This is what allows a camera lens to focus light, because the speed of light is lower in glass than in air
- if you like, entering the glass causes light to travel slower, and re-entering the air causes it to travel faster (ie the original speed)
- It doesn't require an external force to slow it down and then speed it up again.

When we talk about "the speed of light", we imply "speed of light in a vacuum", and we call that c
- Maxwell's equations imply a speed of light in a vacuum c = 1/√(ε₀μ₀)
- ε₀ is the permittivity to electric fields in a vacuum
- μ₀ is the permeability to magnetic fields in a vacuum
- ε₀ and μ₀ can be measured in the laboratory (in a vacuum)

See: https://en.wikipedia.org/wiki/Maxwell%27s_equations#Key_to_the_notation

There are some paradoxes implicit in Maxwell's equations.
- For example, how could every observer measure c = 1/√(ε₀μ₀), when those observers might be traveling at different speeds?
- This was later resolved by Einstein, who showed that while the speed c is the same for all observers, the units of speed (eg meters and seconds) are not the same for all observers.

[Kryptid]

Light travels at a constant velocity  in a vacuum because of ?

Newton's first law.

Lights velocity is ?  Velocity being speed and direction .

About 300,000 kilometers per second in whatever direction it happens to be traveling in.

Light requires a force to pass through glass

Citation needed.

[alancalverd]

No. It is a consequence of Maxwell's equations.

But Maxwell only worked out his equations in the 19th Century.

In all previous centuries, light was going at the same speed, without his equations.
So you surely can't claim that the speed of light is a "consequence" of Maxwell's equations.
That's the wrong way round.

What you should say is that Maxwell's mathematical equations are a "consequence" of the speed of light.

But, does that in any way explain why light goes at that particular speed?

The English language has only existed in recognisable form for about 1000 years, algebra about 1500 years, and differential calculus less than 300 years, so your logic implies that no physical phenomenon can be explained or described by the common tools of science.
Or that nothing happened in the universe before 1700, which is an oxymoron since "1700" presumes that something happened at "0" .
So let's adopt a more conventional interpretation of "consequence".

Maxwell showed that the speed of light is a consequence of well-characterised electromagnetic phenomena. A changing electric field generates a magnetic field and a changing magnetic field generates an electric field. The constants of proportionality define the speed of propagation of the resulting electromagnetic wave in any medium. 

[Michael Sally (OP)]

Is the speed of a light a consequence of ?

Maxwell's equations predicted the possibility of electromagnetic waves.
- Radio waves were discovered soon after, by Hertz and others
- It was also realized that visible light travelled at this speed too, so light must also be an electromagnetic wave

Maxwell's equations imply a speed of light in any material of 1/√(εμ), where:
- ε is the permittivity to electric fields in that material
- μ is the permeability to magnetic fields in that material
- ε and μ can be measured in the laboratory (in that material)
- This equation has some similarities to the equation for the speed of a sound wave in a guitar string.

So when electromagnetic waves (eg light) pass from one medium to another, the values of ε & μ change, and so the speed of light changes.
- This is what allows a camera lens to focus light, because the speed of light is lower in glass than in air
- if you like, entering the glass causes light to travel slower, and re-entering the air causes it to travel faster (ie the original speed)
- It doesn't require an external force to slow it down and then speed it up again.

When we talk about "the speed of light", we imply "speed of light in a vacuum", and we call that c
- Maxwell's equations imply a speed of light in a vacuum c = 1/√(ε₀μ₀)
- ε₀ is the permittivity to electric fields in a vacuum
- μ₀ is the permeability to magnetic fields in a vacuum
- ε₀ and μ₀ can be measured in the laboratory (in a vacuum)

See: https://en.wikipedia.org/wiki/Maxwell%27s_equations#Key_to_the_notation

There are some paradoxes implicit in Maxwell's equations.
- For example, how could every observer measure c = 1/√(ε₀μ₀), when those observers might be traveling at different speeds?
- This was later resolved by Einstein, who showed that while the speed c is the same for all observers, the units of speed (eg meters and seconds) are not the same for all observers.

Maxwell states the term free space and gives values of e0u0 for free space . Quite clearly when light passes through a medium which in example I gave glass , the e0u0 is greater of the glass than free space which applies a ''stopping force'' on lights travel . When the light leaves the medium to re-enter free space , the light then  accelerates to return to c .

This acceleration physically requires a force or the light would maintain the speed it traveled through the medium once it had exited the medium .

 Can we assume from Maxwell's work that light is more attractive to freespace than the volume of the glass block ?

If this wasn't  true , the light would not exit the glass block .

F=  ?

[Michael Sally (OP)]

Maxwell showed that the speed of light is a consequence of well-characterised electromagnetic phenomena. A changing electric field generates a magnetic field and a changing magnetic field generates an electric field. The constants of proportionality define the speed of propagation of the resulting electromagnetic wave in any medium.

Although Maxwell explains field properties , Maxwell didn't explain lights ''engine'' . An ''engine'' which I believe is an attractive force .

My thoughts in quest to discover this ''engine'' are now considering a freespace force .   

From our discussions , I now believe this free space force is something to do with  proportionality and the magnitude of energy . 

≠

[Bored chemist]

 Can we assume from Maxwell's work that light is more attractive to freespace than the volume of the glass block ?

If this wasn't  true , the light would not exit the glass block .

No.
Because, by the same (questionable) argument, it would mean that light couldn't enter the glass block.

[Michael Sally (OP)]

No.
Because, by the same (questionable) argument, it would mean that light couldn't enter the glass block.

Please explain how that means the light couldn't enter the glass block , I think your logic might be flawed in that statement .

I have drawn us another diagram to help us observe the process we are discussing .


cm2.jpg (24.29 kB . 816x460 - viewed 2328 times)

[Kryptid]

Well, that clenches it. I was suspicious that you were Thebox when I saw you posting those nonsensical diagrams, using sentence fragments as questions and claiming that light needs a force to propel it. Now that you've started posting meaningless equations to go with it all, you've given yourself away.

Why do you keep coming back? I recall you once posted a thread asking to be banned and promised not to come back as a sock puppet. So when you were finally banned, why didn't you keep your promise?

[Michael Sally (OP)]

Well, that clenches it. I was suspicious that you were Thebox when I saw you posting those nonsensical diagrams, using sentence fragments as questions and claiming that light needs a force to propel it. Now that you've started posting meaningless equations to go with it all, you've given yourself away.

Why do you keep coming back? I recall you once posted a thread asking to be banned and promised not to come back as a sock puppet. So when you were finally banned, why didn't you keep your promise?

Thebox ?

[Kryptid]

Yes, I am 100% convinced that you are Thebox. Under your "Starlight" sock account, you made the exact same argument about light having to be propelled by a force because it goes faster when exiting glass. I would ban you immediately, but I feel that my fellow moderators also need to be convinced before I do that.

[Michael Sally (OP)]

Yes, I am 100% convinced

You seem to be convinced of a lot of things including light not needing a force to accelerate when exiting a medium .

 I didn't make up any physics of lights nature and have kindly presented a detailed accurate diagram for discussion purposes . Also I have not insinuated any sort of propelled force , my question asks about an attractive force .

I was given an answer that gravity can affect light , could free space have a gravitational constant we have not considered before ?

[jeffreyH]

Oh LeBerx? Bonjour mon ami et qu'est-ce que tu es? Broer, hou op om kind te wees.

[Petrochemicals]

Is the speed of light a consequence of an external force  ?

I'll be honest I can't answer this without it being in new theories as at present know one knows.

There are theories about light being pre programmed and relating to space time, whether light travels through space or is merely ejected when a wave strikes an object.

Thank you for your honest answer but how can a question be a new theory ?

Shouldn't we firstly discuss the possibility of an external force and then discuss what this assumed force may be before finally trying to devise an experiment to test the assumptions ?

Then only if all the above satisfied , write a new theory ?

Light is wierd as hamdani yusuf of this forum  makes lots of posts about. I'm sure you have heard of the double slit.

https://en.m.wikipedia.org/wiki/Modern_physics

Being as questions such as this still remain unanswered light and space remain unexplained.

[evan_au]

ε₀μ₀ for free space ... the ε₀μ₀ of the glass

ε₀ & μ₀ refer specifically to a vacuum (the 0 means "nothing")
- Any other substance does not have the values ε₀ & μ₀, and the speed of electromagnetic radiation is less than c
- Although for air, ε & μ are quite close to ε₀ & μ₀, and the speed of light in air is just below c

Rather than quote specific values for ε & μ, it is often easier to compare them to ε₀ & μ₀ by quoting the ratio with ε₀ & μ₀ (in a particular substance). This gives us ε_r & μ_r, where r means "relative":
- ε_r = ε/ε₀
- μ_r = μ/μ₀

Similarly, rather than quote the speed of light in a particular substance (v), it is often more convenient to quote its ratio with the speed of light in a vacuum (c).
η = v/c is called the refractive index of the material.
In most materials, the refractive index varies with frequency (which is how we get rainbows).

You can find a list of refractive index(es)/indices here:
https://en.wikipedia.org/wiki/List_of_refractive_indices

Please explain how that means the light couldn't enter the glass block

Inability to think outside the box.... Jumbled equations with no consistency in units....

Definitely The Box!

[Bored chemist]

On a philosophical note, if we have a poster who behaves like TheBox, should we treat them the same way that we treated TheBox?