(Blake, FYI, the search terms I used for the board search were “Slow down speed of light” and “speed of light decrease.” It doesn’t want to search for ‘c’ of course. Just keeping you posted!)
What would the world be like if c were, say, 75 miles per hour? Would objects still cohere together the way they do under present circumstances or does their coherence depend on the actual value of c in some way? If objects would cohere, would it be easy to reach the speed of light (75 mph) or would physics now be such that it takes a huge amount of energy to accelerate to that speed? (Meaning everything in the 75mph universe would move very slowly compared to our own).
Well, it depends. The structure of our world is really dependent on the dimensionless constants, so if other natural constants (electron charge e, Planck’s constant h etc.) were to change in a compensating manner, there’d perhaps not be much of a difference.
Failing such compensation, though, for instance the fine structure constant α, which determines the strength of the electromagnetic interaction, will change its value, which, depending on the amount of change, may have disastrous consequences, such as stellar fusion being impossible etc. (Though I’m not certain it’s all that meaningful to consider the varying of α as a consequence of varying c…)
For an entertaining take on the matter, I suggest George Gamow’s Mr Tompkins series, the first instalment of which, Mr Tompkins in Wonderland, deals precisely with the question of how a world with a significantly lower speed of light would look like, and it seems it’s available in full here.
Personally, I wouldn’t even say it’s meaningful for c to change. You might as well ask “What would happen if the value of 1 were to increase?”. It certainly would be meaningful for the fine structure constant to change (whether it’s possible, we don’t know, but it’s meaningful). But personally, if the value of the fine structure constant were to change, I’d rather describe that as a change in the strength of the electromagnetic coupling, rather than as a change in c.
John Stith won the Nebula Award for Redshift Rendezvous, an sf novel set on board an alien starship with a series of levels, each having a different speed of light. The effects are meticulously worked out.
I am not a physicist. But I’ve read that there are some observed phenomena for which known science does not yet have an explanation. For example, there are methods for measuring the ages of distant stars and there are methods for measuring the age of the universe. But when these methods have been applied, scientists have found some stars appear to be older than the universe - an obviously impossible situation.
What I’ve read is that one theory for reconciling these numbers is that the speed of light may not be a universal constant. The measurement methods assumed that the speed of light has always been the same and is always now the same everywhere in the universe. But the premise is that the speed of light we’ve measured may be a “local” constant - billions of years in the past or billions of light years away, it might be different.
I believe that was due to a mismeasurement of the distance of those stars, which led to a misestimation of their true brightness, and a consequent miscalculation of their ages; here’s a webpage that examines that story in detail.
I don’t know about this being proposed as a resolution of the ‘old stars’ problem, but variable speed of light cosmologies indeed exist, mainly to address the problem of the uniformity of the microwave background – from all directions in the sky, the CMB is uniform to an extreme degree, indicating that the universe at the time the radiation was emitted must have been a highly uniform temperature; but in standard cosmology, there was no time for that – the different regions are too far away from each other to have had any causal interaction. How then could they have agreed on a temperature with one another?
However, if you postulate a speed of light that was higher in the past, then the problem goes away, as causal contact can be established over greater distances.
But, while this does pose a possible solution, it’s not widely accepted – the more common idea is that of inflation, in which the universe in its earliest stages underwent an exponential expansion, so that the entire universe was causally connected in the past, but then was ‘blown up’ to what we see now.
The “old stars” problem was due to a variety of errors, in astronomy, astrophysics, and cosmology. All of these errors have now been refined (mostly in astrophysics), and the problem has been resolved.
Tangentially related, Vernor Vinges “A Fire Upon the Deep” supposes a galaxy where the speed of light increases as you move away from the galactic centre (and there’s a bunch of other effects as well)… damn good read.
Thinking it out, they’d have the same amount of kenetic energy, and since kinetic energy needed for a speed is a function of that speed relative to c (it’s a lot of easier to accelerate from a relative dead stop than .9999 the speed of c).
My thinking is that’d mean the speed of everything in the universe would change, if c changed. Is that correct?
I was afraid of something like that, the whole everything moves the same speed relative c, but things move different speeds relative to me kind of ties my head in knots.
Let’s say units of distance covered over a time measured by the rate of change of a clock on earth. So a clock with some speed but not, in most reference frames, a speed near c, if that makes any sense.
Edit: further let’s say I’m setting right by the clock so it a speed of zero relative to me, and using it to measure the speed of other objects passing by. If that helps.
You need to specify your clock, and also how you’re specifying units of distance. Here, I’ll help you out by giving some examples:
1: Define a “meter” as the length of a particular rod of metal (one should also specify temperature and so on, and then you need a way of defining temperature, but we’ll gloss over that for the sake of simplicity). Now build a clock by putting a mirror at each end of that rod, and shooting a laser in between those mirrors. Define a “second” as the time that it takes for the laser beam to bounce back and forth 299792458 times.
Clearly, under this definition, the speed of light will always be 299792458 m/s, but that’s not very interesting.
2: Define a “meter” as the length of a particular metal rod. Now construct a clock by suspending a point mass from a massless suspension of length 1 meter, and set it oscillating at small angles in the Earth’s gravitational field (we have issues now with the point mass and the massless suspension, and we have to specify exactly where on Earth we mean, but again, these are details). Define a second as 1/2.00640929 times the time it takes this pendulum to make one complete oscillation.
OK, now it’s conceivable that when we repeat the experiment, we’ll find a different value for c in meters per second. But wait, you’ll say, maybe that just means that our units are changing. Maybe something happened to our metal rod, for instance, so our meter isn’t always the same length. Let’s take care of that.
3: Define a “meter” as the length of a metal rod consisting of a cylinder certain number of platinum atoms long and a certain number of platinum atoms in diameter. Now construct a clock and define a second as in 2.
OK, now we we’ve taken away some of the worry about our rod changing. If it changes the number of atoms, or if some of the platinum atoms are replaced with some other element, or whatever, we can just change it back before repeating the experiment. But we still have to take it on faith that the size of the platinum atom hasn’t changed. And we also have the possibility that the mass of the Earth is changing.
4: As 3, except now instead of using the Earth, we use a fixed number of protons, neutrons, and electrons to generate our gravitational field.
OK, but now, we have to deal with the possibility that the mass of the proton is changing.
We can continue like this for a long time, but suffice to say that, no matter what experiment you can come up with that purports to show the speed of light changing, one can always come up with something else that might be changing, and say that maybe your experiment is just showing that that something else is changing while c remains constant.
Sorry to have not read your whole post, but doesn’t “there is no meaning to the phrase ‘the value of c changes’” imply “there is no meaning to the phrase ‘c=x’” for any x?
No, it means our system defines c as = 1, and if you change it, the value of 1 is changed. Or c, but you can’t tell the difference.
Time is defined by vibrations of sub atomic level objects. Those vibrations take place over distances, at particular levels of energy. If c changes, is it the distance light travels that changes, or the magnitude of time that passed? You cannot tell. Might be the length those particles had to travel to vibrate, or the amount of energy present at the particular temperature you used. So, we define the second one way, and distance the other, as a standard, but in observation, we still cannot say which element changed.
I remember a few years ago a report that a certain observation of red shifted light indicated that either the strength of electron coupling was different by some miniscule fraction of a percent, or that light was slower by some proportional miniscule fraction of a percent over the multiple billions of years necessary for us to have observed it. Most of what I read about it since simply stated has said, naah, it’s a mistake in observation. Has to be, since if there had been a change in either at any time in the history of the universe, the observation would necessarily be a fundamental property of all observations of objects at that distance, or any distance greater.
