What Properties Might Light of Millennia Past Have that Today's Doesn't?

Do you know me well enough to have a guess about what I may have considered?If you do some reading, you'll find that we've had any number of threads here in which we've discussed the ramifications of a changing speed of light. So no, you aren't asking any new questions.If you have an argument to make about properties in the light in the past, and how they may have been different than today, why don't you get to it? Don't worry about whether I can keep up.

No.

No, Limpy, the universe expanding could not be observed in principle. It's just an incoherent idea. Like velocity is getting brittle. These two notions do not make any sense together. It takes two entities to expand. The Universe is one and only. End of story.

No, Alfy, observations are consistent with an expanding universe. http://skyserver.sdss.org/dr1/en/astro/universe/universe.asp Not only is it expanding, the expansion is also accelerating Accelerating expansion of the universe - Wikipedia

The fine structure constant is dimensionless and can be defined in terms of the permeability of free space, the speed of light in a vacuum, the elementary charge and the reduced plank's constant.In a scheme of things where the fabric of space itself is changing by means of the zero point energy, all of the above terms are also changing and changing in a way that keeps the fine structure constant....constant. Since it can be constant with a changing speed of light, no need to conjure up ideas about carbon life being impossible.

Planck's constant, the speed of light and the permeability of free space all have units. So an alien race who measured things differently might not have these constants.For example humans traditionally measure Energy and Frequency using different units. However we know, from light for example, that Energy and frequency are really the same things and "should" be measured using the same units. A single units of frequency is "really" Joules and this is what Planck's constant records.Only dimensionless quantities have a real existence outside of our mismatch of units. Hence this whole discussion should only be about the fine-structure constant and not the speed of light, as it is the fundamental quantity. Edited by Son Goku, : Latex

The problem, as has been pointed out repeatedly, is that changing all of those other 'constants' does have ramifications for life in the universe and life on earth. But it seems that once the discussion turns to discussing those ramifications, and the fact that those changed constants lead to results we ought to be able to observe, you lose all interest in the discussion. It's as if Devil Woman had never been written.For example, are you seriously suggesting that changing the charge on a proton will have no affect on nuclear fusion? Aren't you going to have to change even more constants to get that to work out?

I've never really understood this argument. We might measure the speed of light in furlongs per fortnight. But we also would not expect anything regarding how the universe operates to change because we have done so. Or because we use the English system rather than the metric system, or because we use units based on the orbital rotation of Zormicron and the length of an Acron's nose. The values of those non-fundamental constants includes their units, and we can readily convert from any one set to another using well understood methods.

The basic point is that dimensionful constants can always be eliminated from equations of motion. Basically there is no way to distinguish, really, between a change in 'c' and a change in your units of distance. The only "real" change independent of your unit system, would be a change in the fine structure constant.Basically any change in units that alters physics can be fundamentally reduced to a change in the fine structure constant or other dimensionless constants. However there are variations of dimensionful constants that are indistinguishable from a change in units and hence have no physical meaning.

I appreciate your patience, but I am still struggling with this idea. I see a distinction between c being 3.0 * 10^8 in MKS units and being 6.0 * 10^8 in the same units, because that change would have an affect on matter/energy equivalency. On the other hand, the fact that c is also about 186,282 mi/sec does not have that same effect.In what sense are the two type of "changes" in the speed of light indistinguishable? Or alternatively where can I find these ideas presented?

I don't care how many times it has been repeated; it is merely your assertion and nothing more. All of the constants are derived from a deeper reality and they don't change alone but in tandem. This tandem change keeps all the ramifications that you insist would happen from happening. I lose interest because you guys have plugs in your ears and I hate all the inenvitable sarcasm that always comes in some people's posts and there is no one that can screen out those posts from my eyes and so I will blow up and get banned. Instead of getting banned, I post until I see the usual sarcasm and condension getting posted and then I scram and don't come back or I start reading other topics.

You think you can change the fundamental constants in ways that would change just one aspect of our universe, such as c, without changing anything else. It would be best if Son Goku or Cavediver would comment, but I think what people are trying to tell you is that that can't happen. If that's correct then I see no reason why you should just accept this answer without understanding why it is true. But acquiring that understanding might represent a considerable investment in time, and unless you do that you have no excuse for rejecting the answer. Don't get so angry that you forget about Report Discussion Problems Here 3.0.--Percy

Nobody has yet been able to find a set of changes, in tandem or not, that are consistent with observations. That includes you. For some specifics, here's physicist Steve Carlip on Barry Setterfield's "theory" and stars and planets:

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Here's the upshot. The minimum number N of nucleons (protons and neutrons) needed for a star to "ignite" goes as (a/a_G)^{3/2}. From point (1), Setterfield's a is constant; from point (4), his a_G goes as 1/c^2. Hence his N goes as c^3. The present value of N is a few percent of the number of nucleons in the Sun. Thus in Setterfield's model, an increase in c by a factor of a little more than 2 will turn off the Sun. Setterfield has various "fits'' of the rate of change of c, but by my reading this would have been about 1000 years ago. I think it would have been noticed.

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You get an even more dramatic dependence on c if you ask about the energy output, or luminosity, of a star. This goes as (a_G)^4 (see Barrow and Tipler, section 5.6), or, in Setterfield's model, c^{-8}. A 10% change in c would thus cut the luminosity of the Sun by a factor of two. Setterfield would have this happen in the past 600 or 700 years, I think. Again, it would have been noticed.

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You run into the same sort of problem if you look at the sizes of planets. A planet is in equilibrium when gravitational attraction, which changes in time according to Setterfield, balances repulsive forces, which don't. The radius of a planet depends on quantities that vary, in Setterfield's model, as (a_G)^{-1/2}(m_e)^{-1}, where m_e is the mass of an electron (see Barrow and Tipler, section 5.3). This varies, according to Setterfield, as c^3. Thus a 10% decrease in the speed of light -- in the past 700 years! -- would have meant about a 30% decrease in the radius of the Earth. Again, this would have been noticed.

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And here he is again, on various aspects:

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There is overwhelming evidence that the speed of light (c) has not changed substantially in a very long time.

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Let's start with the most precise. Atoms emit light at certain precise energies, which are determined by a constant called the fine structure constant, a (that should really be alpha, but ASCII doesn't do Greek). Now, a=e^2/hc, where e is the charge of an electron and h is Planck's constant. Changes in c would result in corresponding changes in a, which would in turn shift spectra. It's slightly more complicated than that (observed spectra are also affected by red shift, so you need to compare different spectral lines to extract the fine structure constant), but still fairly straightforward. Such observations give a limit on the change in c of less than about a part in 10^15 per year, over most of the history of the Universe.

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Now, you can try to get around this by suggesting that h or e also change, in exactly the right way to cancel changes in c. But that would mean that any clock based on electromagnetic interactions (quartz clocks, atomic clocks, etc.) would give the usual, unchanged speed of light; more on this below.

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Next, consider radioactive decay. For a period after the initial explosion of a supernova, much of the energy that emerges that we observe comes from the radioactive decays of cobalt-56 and cobalt-57. These decays can be identified because they emit gamma rays of very precise frequencies, which are easily detectable. We've looked at the decay rates from the most recent nearby supernova, SN1987A, and they're exactly the same as the ones we observe in the laboratory. But the decay rates go as c^4, so c cannot have changed significantly.

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Again, you can try to get around this by suggesting that some other constant -- in this case, the Fermi constant -- also changes, in exactly the right way to cancel changes in c. But that would mean that any clock based on weak interactions would give the usual, unchanged speed of light.

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Next, consider electron-positron annihilation. This process results in the emission of two gamma rays, with energies E=mc^2, where m is the electron mass. Changing c would change this energy. Observations of such annihilation radiation from fairly large distances -- the center of our galaxy, for example, which is about 30,000 light years away -- gives a limit on changes in c. It's much weaker than the limits from observing spectra, but it's still easily strong enough to exclude any "drastic" change.

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Again, you can try to get around this by suggesting that m also changes, in exactly the right way to cancel changes in c. But this would mean that any clocks based on such annihilation processes would give the usual, unchanged speed of light.

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Next, consider gravitational processes. Fusion in a star depends on a delicate balance between gravity and electromagnetism. A star must have a large enough mass to overcome the electric repulsion between protons, allowing them to get close enough to fuse; but a star that is too heavy becomes unstable against radiation pressure. A fairly easy calculation -- see Weisskopf, Science 187 (2/75) 605 for a beautiful explanation that uses only fairly elementary physics -- shows that a normal star must have between about 10^56 and 10^59 nucleons. But this number goes as c^3/2, so relatively small changes in c would, essentially, put out the stars. Things get even worse if you also have masses changing with time to keep the electron-positron annihilation energy consistent with observation; then you get a variation that goes as c^3 instead. It's even worse if you look at the luminosity rather than just the stability of stars. A 5% increase in c would dim the Sun enough to freeze the Earth's oceans, while a 12% decrease or so would boil the oceans. You run into the same problem if you look at the radii of planets, which depend on a balance between gravity and various repulsive atomic forces. This balance depends on the speed of light; changes in c by a few percent would change the radius of the Earth by a few percent (which would have been noticed!).

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Again, you can try escape by suggesting that something else -- in this case, Newton's gravitational constant -- also changes, in exactly the right way to cancel changes in c. But this would mean that any gravitational clocks would give the usual, unchanged speed of light.

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In short, a huge number of observations (I've given only a sample) rule out any significant changes in the speed of light. In each case, you can evade the conclusion only by postulating that other constants change in just the right way to cancel the effects. But in the end,that means that any *physical measurement* of c would show no change. Similarly, if you use this to argue for a young Earth, you end up with a theory in which the Earth is "young" but all possible measurements of its age give an "old" answer. The kindest thing I can say about that is that it requires one to use definitions of words like "young" and "old" that have little to do with their usual meanings. ("I'm only 24 minutes old, because what you call a year is what I call 30 seconds.")

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The takeaway is that you don't just claim "in tandem" and walk away. You have to do calculations and demonstrate that the changes you propose are in accordance with our observations. This isn't a simple task (Setterfield's been trying for decades and hasn't succeeded yet). And you have to know a lot of physics just to know what observations are relevant and must be addressed (as you can see from the above, the ramifications spread into areas you might not consider without the appropriate knowledge)Oh, and here's a link to one of Steve's articles on universal constants. Well worth reading, with a link to a significantly technical paper on the subject.

removed to avoid dogpileEdited by NoNukes, : Better explained by others.

No worries, it's an odd idea and I didn't explain it well. Let's take two universes with these two different values of c, but with the same value of alpha, the fine structure constant. It would turn out that the laws of physics work out exactly the same, except that in the universe with those laws of physics play out twice as fast. So what takes 2 units of time in the first universe takes 1 unit of time in the second universe.Hence it's just the same universe viewed using two different measurements of time. The units of one system are worth twice the units of another system.It's only if you changed alpha that you would get a universe that couldn't be understood as the same universe sped up or slowed down.A better example might be a world where the North-South distance along the Earth is measured using furlongs and the East-West distance using meters. Then in geographical calculations you'd always have a constant D = 0.005 furlongs/meter, when computing areas. You could ask what would happen if D changed value, but it is meaningless, it would just be a redefinition of the meter or the furlong (or both).