# What if the speed of light was slower?

1. Dec 28, 2003

### TheDonk

If the maximum speed was say a 10th what it is, would it have any drastic changes in the universe?
I guess there would be more and bigger black holes and light would take longer to reach us, but what would be the main differences in the universe? Would it be much different?

2. Dec 28, 2003

### Staff: Mentor

C is one of those constants which if it were much different, would radically alter the structure of the universe. Just off the top of my head, since C is important to the matter/energy conversion going on in the sun (fusion), cutting C to 1/10 would decrease the output of the sun to 1/100 - assuming the rate of fusion is unchanged (it would change).

3. Dec 29, 2003

### Integral

Staff Emeritus
Find a copy of Mr. Tompkins in Wonderland by George Gamov.

4. Dec 31, 2003

### TheDonk

The real point of this question was to see if there wasn't much difference whether light was slower or not. This was because I wanted to ask this second question:
Instead of the universe expanding at an accelerating speed could it be that the maximum speed of light has been increasing?

5. Jan 4, 2004

### HallsofIvy

George Gamow wrote some children's books ("Mr. Tompkins in Wonderland" was one, I think) that are now available as "Mr. Tompkins in Paperback" from Amazon.com: https://www.amazon.com/exec/obidos/...2-6569112-3635366?v=glance&s=books&vi=reviews

in which he talked about what would happen if the speed of light were a few meters per second or if Plank's constant were very large.

Last edited by a moderator: May 1, 2017
6. Jan 4, 2004

### lethe

changing the speed of light would not change anything about the universe at all.

this is because the speed of light is a dimensionful number. if you were to change it, all you would do would change the size of the meter. but relative to this new meter, the universe would look exactly the same.

on the other hand, changing the fine structure constant, or changing the electron mass, would change the universe quite drastically.

usually when people talk about a variable speed of light, they are actually talking about a variable fine structure constant.

7. Jan 4, 2004

There is some evidence to suggest that the speed of light has indeed changed somewhat over the course of the universe's development.

8. Jan 4, 2004

### Integral

Staff Emeritus
I believe that this is a topic of current research. Some results say yes, others no. It is still undecided as far as I know.

9. Jan 4, 2004

### lethe

there is some evidence to suggest that the fine structure constant has changed.

as i said above, changes in the speed of light are inobservable since it is a dimensionful constant.

so i believe your statement is mistaken.

10. Jan 4, 2004

Lethe

Yes, you're quite right. I just re-read the articles about it. They say the observations suggest the FSC may have been a tad smaller a long time ago.

11. Jan 7, 2004

### HeyCharley

This concept is really interesting in that if you change the value of c slightly slower, this (obviously) means that c has increased. We've recently discovered, supposedly, that the universe is expanding, and in an accelerating fashion. If the extreme concepts of so-called "string" theory are to be applied, I wonder if C is a factor of the total lenght of the "string," which is expanding.

12. Jan 11, 2004

### Nereid

Staff Emeritus
observational evidence of changes in the FSC

While keeping an open mind and always searching for more and more stringent tests is 'a good thing', IMHO the observational data on changes in the fine structure constant (FSC) over cosmological time is overwhelmingly in favour of the hypothesis that it is, truly, constant.

AFAIK, there've been no reported new 'many multiplet method' determinations of changes in the FSC over cosmological time since January, 2003 (or any other observations of such changes). More specifically, nothing better (in the public domain) than the beautifully clear approach (and unambiguous result) of Bahcall, Steinhardt and Schlegel. If only all astronomical research were so straight-forward
http://arxiv.org/abs/astro-ph/0301507

13. Jan 12, 2004

### TheDonk

How could there be no difference if you changed the speed of light to, let's say 1 meter per second?

I also don't understand how it being a "dimensionful number" would make a difference because it's ratio with all the other constants would be different.

14. Jan 13, 2004

### lethe

if the speed of light were one meter per second, then atoms would be smaller, information would move more slowly across distances about the size of a meter, and a meter would seem extremely huge to us. how huge? in this hypothetical universe, a meter would seem as huge to the inhabitants of that universe as a light-second seems to us in this universe.

the geological processes that shape the earth wouldn t be able to cover distances on the order of meters, and the earth would be much smaller, but that would be OK, because the radius of the atoms that make up the earth would be much smaller.

in fact, if i replace the word meter with light-second, then i would be describing the same universe. all i did was change the units.

this is why changing a dimensionful number has no meaning. our units are defined in terms of the fundamental constants. change the fundamental constants, and you change the units. but you don t change the size and shape of the universe, you have only changed the name of your meter stick.

15. Jan 13, 2004

### TheDonk

Alright, all of that makes sense except one thing for me.
Why would the atoms become smaller?
Is it because it takes more energy for their subatomic parts to move around? If so, why does this show that the ratio of the atom's sizes would be exactly the same as the ratio between the light speeds.

16. Jan 15, 2004

### young e.

I think there would have less potential life on earth because in relativistic approach in explaining why is it that the sun keep on shining for billion of years it rely on einstiens energy equation. So if it happens then there will be less conversion of hydrogen into helium from the sun and the sun rays which sustains life on earth will be lesser so thats it.

17. Jan 19, 2004

### Nereid

Staff Emeritus
Universe changed if WHICH constants change?

So that's:
$$c$$ ("speed of light"): no change
$$\alpha$$ (fine structure constant): big change
$$e$$ (elementary charge): change (big?)

What about other 'fundamental physical constants'? As you find on the NIST site:
http://physics.nist.gov/cuu/Constants/index.html
particularly hbar, G, k

18. Jan 19, 2004

Staff Emeritus
Re: Universe changed if WHICH constants change?

But since the fine structure constant is a function of c and e:

$$\alpha = \frac{e^2}{hc}$$

any change in either would mean a change in $$\alpha$$

19. Jan 19, 2004

### Nereid

Staff Emeritus
Re: Re: Universe changed if WHICH constants change?

Thanks.

I'm interested to know which set of independent physical constants would make a big change in the universe - if different from what they are here and now.

lethe said "this is why changing a dimensionful number has no meaning. our units are defined in terms of the fundamental constants. change the fundamental constants, and you change the units. but you don t change the size and shape of the universe, you have only changed the name of your meter stick"

What are the constants that really matter?

20. Jan 19, 2004

### lethe

Re: Re: Re: Universe changed if WHICH constants change?

the dimensionless constants. this website has a list of the dimensionless constants. i think there are 26 of them, in the standard model.