## Expansion speeding up

Got a beginners' question? No matter how elementary, our friendly forum community and magazine writers will answer it.

### Re: Expansion speeding up

Gfamily2 wrote:You've not said how you think this red shift is measured. Please explain this first.

Now, why do you say that gas and dust would slow down light ?

How much does the light slow down by - lots or just a little? Typically, how much slower do you think light slows down, and does the light get progressively slower and slower, or does it just slow down when it enters the 'gas and dust'? How would you prove this?

How are the 'slowing down' and the 'red shift' related?

On your first point about how the "Red-shift" is measured, well it's done with glass prisms.
The glass slows down the light. Hydrogen gas does the same thing. And as hydrogen gas is everywhere in the Universe, so it gives a Universal background Red-shift.

The extent of the Red-shift, depends only on variations in the density of the gas. Just as telescopes work, by employing variations in the the density of air and glass.

On your second point, about why light is slowed down by gas and dust, well obviously it's because the photons of light hit the gas and dust molecules, which obstruct the photons' progress. If the photons were travelling through a pure vacuum, they'd go unhindered at the speed of light. The gas and dust slows them down.
david48

Posts: 173
Joined: Mon Feb 13, 2012 7:13 pm

### Re: Expansion speeding up

david48 wrote:
Gfamily2 wrote:You've not said how you think this red shift is measured. Please explain this first.

Now, why do you say that gas and dust would slow down light ?

How much does the light slow down by - lots or just a little? Typically, how much slower do you think light slows down, and does the light get progressively slower and slower, or does it just slow down when it enters the 'gas and dust'? How would you prove this?

How are the 'slowing down' and the 'red shift' related?

On your first point about how the "Red-shift" is measured, well it's done with glass prisms.
The glass slows down the light. Hydrogen gas does the same thing. And as hydrogen gas is everywhere in the Universe, so it gives a Universal background Red-shift.

The extent of the Red-shift, depends only on variations in the density of the gas. Just as telescopes work, by employing variations in the the density of air and glass.

On your second point, about why light is slowed down by gas and dust, well obviously it's because the photons of light hit the gas and dust molecules, which obstruct the photons' progress. If the photons were travelling through a pure vacuum, they'd go unhindered at the speed of light. The gas and dust slows them down.

Start again - How is the red shift measured? Give a full answer, one that gives a measurement in terms of units of something scientific.

When you say "the glass slows down the light. Hydrogen gas does the same" does this mean that looking through a pane of glass should make the light look red? Does it? Why not?
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
(Not a moderator)
Gfamily2

Posts: 517
Joined: Thu Jun 25, 2015 10:38 pm

### Re: Expansion speeding up

Gfamily2 wrote:
david48 wrote:
Gfamily2 wrote:You've not said how you think this red shift is measured. Please explain this first.

Now, why do you say that gas and dust would slow down light ?

How much does the light slow down by - lots or just a little? Typically, how much slower do you think light slows down, and does the light get progressively slower and slower, or does it just slow down when it enters the 'gas and dust'? How would you prove this?

How are the 'slowing down' and the 'red shift' related?

On your first point about how the "Red-shift" is measured, well it's done with glass prisms.
The glass slows down the light. Hydrogen gas does the same thing. And as hydrogen gas is everywhere in the Universe, so it gives a Universal background Red-shift.

The extent of the Red-shift, depends only on variations in the density of the gas. Just as telescopes work, by employing variations in the the density of air and glass.

On your second point, about why light is slowed down by gas and dust, well obviously it's because the photons of light hit the gas and dust molecules, which obstruct the photons' progress. If the photons were travelling through a pure vacuum, they'd go unhindered at the speed of light. The gas and dust slows them down.

Start again - How is the red shift measured? Give a full answer, one that gives a measurement in terms of units of something scientific.

When you say "the glass slows down the light. Hydrogen gas does the same" does this mean that looking through a pane of glass should make the light look red? Does it? Why not?

1. Could you please clarify your request for Red-Shift to be measured in terms of "units of something scientific", as I'm not sure what that means!

2. As regards the pane of glass, glass certainly can alter colours, when it's in a spherical shape. Such as a spherical glass telescope lens. That produces chromatic aberration, ie red and blue colours that aren't real. The colours are generated by the medium of the spherical glass. And the Universe is supposed to be spherical. So couldn't it also produce through the medium of hydrogen gas, a kind of chromatic aberration, ie a "Red-shift", that equally isn't real?
david48

Posts: 173
Joined: Mon Feb 13, 2012 7:13 pm

### Re: Expansion speeding up

1. Could you please clarify your request for Red-Shift to be measured in terms of "units of something scientific", as I'm not sure what that means!

Yes, I was beginning to come to the same conclusion.
"units of something scientific" means "something that means something to science".

So, when we're looking at distant galaxies, what do YOU think astronomers do when they're looking for a red shift? That's what I mean when I as for something measured in "units of something scientific"? What do YOU think they are they measuring when they measure the red shift ?

If you don't know that (and it looks like you don't even know what the question means), what makes you think you are in any position to come up with an alternative explanation - when you don't even know anything about what the existing explanation means?
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
(Not a moderator)
Gfamily2

Posts: 517
Joined: Thu Jun 25, 2015 10:38 pm

### Re: Expansion speeding up

2. As regards the pane of glass, glass certainly can alter colours, when it's in a spherical shape. Such as a spherical glass telescope lens. That produces chromatic aberration, ie red and blue colours that aren't real.The colours are generated by the medium of the spherical glass.

Right, so you don't understand the cause of chromatic aberration either. Newton would despair - he understood. Unless you think you have a new explanation for chromatic aberration too.
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
(Not a moderator)
Gfamily2

Posts: 517
Joined: Thu Jun 25, 2015 10:38 pm

### Re: Expansion speeding up

Gfamily2 wrote:
2. As regards the pane of glass, glass certainly can alter colours, when it's in a spherical shape. Such as a spherical glass telescope lens. That produces chromatic aberration, ie red and blue colours that aren't real.The colours are generated by the medium of the spherical glass.

Right, so you don't understand the cause of chromatic aberration either. Newton would despair - he understood. Unless you think you have a new explanation for chromatic aberration too.

Well that's not actually true. Newton didn't really understand chromatic aberration.

He thought that the aberration was the inevitable result of light getting refracted by passing through glass. And that, crucially, it didn't matter what kind of different glass was involved, ie whether it was crown-glass or flint-glass.

That's why he gave up on refractors, and invented his Newtonian reflecting telescope.

Of course Newton was dead wrong. A refracting telescope with a properly computed compound OG , consisting of different crown-glass and flint-glass elements, can largely cancel out the chromatic aberration, and produce an achromatic image. The image is even better, and more colour-free, if a the OG is a triplet, as in modern "apochromatic" refractors.

I've always thought that Newton's failure to recognise the true cause of chromatic aberration, was a major and surprising blunder on his part, which retarded the progress of telescopic astronomy for about 100 years.
david48

Posts: 173
Joined: Mon Feb 13, 2012 7:13 pm

### Re: Expansion speeding up

david48 wrote:
Gfamily2 wrote:
2. As regards the pane of glass, glass certainly can alter colours, when it's in a spherical shape. Such as a spherical glass telescope lens. That produces chromatic aberration, ie red and blue colours that aren't real.The colours are generated by the medium of the spherical glass.

Right, so you don't understand the cause of chromatic aberration either. Newton would despair - he understood. Unless you think you have a new explanation for chromatic aberration too.

Well that's not actually true. Newton didn't really understand chromatic aberration.

He thought that the aberration was the inevitable result of light getting refracted by passing through glass. And that, crucially, it didn't matter what kind of different glass was involved, ie whether it was crown-glass or flint-glass.

That's why he gave up on refractors, and invented his Newtonian reflecting telescope.

Of course Newton was dead wrong. A refracting telescope with a properly computed compound OG , consisting of different crown-glass and flint-glass elements, can largely cancel out the chromatic aberration, and produce an achromatic image. The image is even better, and more colour-free, if a the OG is a triplet, as in modern "apochromatic" refractors.

I've always thought that Newton's failure to recognise the true cause of chromatic aberration, was a major and surprising blunder on his part, which retarded the progress of telescopic astronomy for about 100 years.

Easy to have 20-20 hindsight isn't it
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
(Not a moderator)
Gfamily2

Posts: 517
Joined: Thu Jun 25, 2015 10:38 pm

### Re: Expansion speeding up

Yes, Gfamily, as you say, it's easy to have 20/20 hindsight. Such hindsight can even lead us to falsely imagine that we were always right!

As an example of this, I'd like to quote two passages from a Patrick Moore book: his "Guide to Mars". This book went through many editions. In my home library, I have two editions. One published in 1960, the other in 1977.

They both contain a discussion of the so-called "Wave of Darkening" on Mars. This was a supposed seasonal cycle on Mars, which spread from the polar caps to the equator, and made the surface become darker as the Martian "Spring" progressed. The darkening was attributed to new vegetation, sprouting up as the ice-caps melted in the Spring, releasing water to fertilise the vegetation. That was the supposed effect.

OK. Now in the 1960 book, written before the Mariner-9 space-probe arrived at Mars, Moore wrote:

There can be absolutely no doubt that the effect is real...as the Wave of Darkening spreads towards the equator, alterations take place... Syrtis Major darkening perceptibly... alterations occur so regularly that they can be predicted... dark areas spreading...these changes are intimately connected with melting of the polar caps...

But in the 1977 book, written after Mariner-9 had arrived at Mars, and busted his views, Moore writes:

About the "Wave of Darkening" - I do not believe in it, and I never have.

Oh yeah?
david48

Posts: 173
Joined: Mon Feb 13, 2012 7:13 pm

### Re: Expansion speeding up

That's all very well - but what about your proposition that the red shift we see for distant galaxies is caused by clouds of hydrogen? Your proposition seems to imply that they are all EXACTLY aligned so that we only see the 'red' chromatic aberration caused by your proposed lenses of intergalactic gas You say yourself that your cheap refractor views sometimes gave a red fringe and sometimes a blue fringe. Why on Earth would we only ever see the blue?

Also - do you have any reference for a telescope that has a 'spherical glass telescope lens' - that would be a wonder indeed. Feel free to tell me of any telescope with a spherical objective lens.

I'd also be interested in how exactly Newton's views 'retarded the progress of telescopic astronomy for about 100 years'. Do tell.
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
(Not a moderator)
Gfamily2

Posts: 517
Joined: Thu Jun 25, 2015 10:38 pm

### Re: Expansion speeding up

Thanks Gfamily. Your posts are extremely valuable, in that they stimulate thinking. Which is what Science needs - clear thinking.

1. About the red-shift displayed in the spectra of distant galaxies, being caused by clouds of hydrogen gas. I've already explained in previous posts, that this is most likely caused simply by our having to view them through the gas. . The gas makes the light appear red-shifted.
Just as fog can cause terrestrial white lights to look yellowish, ie red-shifted, when viewed through the fog.

2. About the spherical lenses in telescopes, well obviously the lenses are not literally "spherical". (Although a very high-power Huyghenian eyepiece can have an eyelens which is so steeply curved as to be almost hemispherical). I mean that lenses are generally ground with surfaces generated from sections of a sphere. And are not "parabolised" like good telescope primary mirrors are. Of course these days, some expensive binoculars, do contain "aspheric" lenses, but these are difficult to produce. In general, telescope lenses have sphere-based surfaces.

3. About my claim that Newton retarded telescope progress by 100 years, on consideration I concede this may have been an exaggeration. I should have said 50 years. The first achromatic telescope OG's were made in the 1720's, almost contemporaneous with Newton's lifetime. But because of his immense prestige as a scientist, in declaring them impossible, they didn't catch on until the second-half of the 18th Century.
So I think 50 years retardation is more accurate
david48

Posts: 173
Joined: Mon Feb 13, 2012 7:13 pm

PreviousNext