# What happens if you change the fine-structure constant?

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1. Apr 2, 2015

### Brian Sweet

I've read online that the fine-structure constant (alpha) is at a sort of "goldilocks value" for life generation; if it were 4% lower, stars would not produce carbon or oxygen in their fusion, and if it were greater than 0.1, fusion simply wouldn't occur. These are interesting facts, but can anyone tell me what else might change if alpha were at a higher or lower value? Say, a ten percent increase or decrease? Would it affect the speed of light, gravity, atomic bonds, or other fundamental forces?

The alpha constant interests me because it is linked to so many other constants in physics. Originally I wanted to know about the Heisenberg uncertainty principle and how it might be affected by a change in the Planck constant, but most answers from physicists online said that changing Planck's constant is essentially meaningless because it has units, so to change its definition one must change the alpha constant. Even more fascinating is the idea in several articles I read that the alpha constant might be changable over time and space, so asking what would happen isn't a purely hypothetical exercise.

Thoughts?

2. Apr 3, 2015

### Staff: Mentor

No. Actually, our definition of length comes from the speed of light - you cannot change the speed of light, all you could do is making things smaller or larger (or faster/slower). The size of objects depends on the fine-structure constant. A larger fine-structure constant would make the electrons bind more tightly to nuclei, make atoms smaller (which also makes macroscopic objects smaller) and increase chemical binding energies. The opposite direction would have the opposite effects.

There is no known relation between fine-structure constant and gravity.

Changing values of constants that are not dimensionless is meaningless, right. All you can do to change physics is changing the value of dimensionless constants. There are 19 of them in the Standard Model (not including neutrino masses and mixing).

3. Apr 3, 2015

### Brian Sweet

A follow up-question: there's an equation that links the alpha constant to e, c, and Planck's reduced constant, so if it were possible to keep two of those variables constant (say, e and c) while changing alpha, would that produce a meaningful change in the "value" of Planck's constant?

4. Apr 3, 2015

### Staff: Mentor

The question "what stays constant" depends on your unit system then, and unit systems are arbitrary.

5. Apr 3, 2015

### Khashishi

It's not a question of possibility. We can choose which dimensional constants to hold constant and which ones to change. The choice is completely arbitrary. The idea of a dimensionless constant is that these are the only constants that are not arbitrarily defined by us.

Ponder for a moment if it is possible to detect a change in the speed of light. Well, what are we measuring the speed of light against? Are we measuring in meters per second? We would need some way of specifying what a meter is without making use of the speed of light, because that would be circular. The official definition of a meter is "the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second." So you see the problem here?

6. Apr 3, 2015

### Brian Sweet

So you're saying that the change in a dimensional constant (like c) would be undetectable to us because they define their own units?

That much makes sense. I guess my point of confusion is that the fine-structure constant is a ratio (thus, dimensionless), so if you change its value, you can mathematically satisfy the equation by changing one or more values on the other side of the equation. But you're saying that such a change would be arbitrary because of our unit systems, correct?

7. Apr 3, 2015

### Staff: Mentor

Right.
Right. Only the dimensionless product has physical relevance.

8. Apr 3, 2015

### Brian Sweet

Okay, thanks for clearing that up!

I'm trying to get a handle on the concept for a story idea: specifically, the idea that future technology could alter the alpha constant within a given field. From what I understand now, changing the alpha constant in an area would shrink/enlarge the atoms within it, right? I'm assuming that, at some point, the bonding energy would either become too weak to form atoms at all or so strong that they collapse. Am I way off on this assumption?

Also, since Planck's constant IS a component of the ratio, would a change in alpha affect quantum behavior in physics?

9. Apr 3, 2015

### Khashishi

When we make measurements things with dimensions, we do so in terms of some standard values, like a meter, or a second. This works well in practice, because these standard values are mostly not changing, so we know a meter is a meter is a meter, and if something measured 1 meter yesterday and 2 meters today, we know it doubled in length.

But when we start talking hypothetically about other universes, and varying fundamental constants, we can no longer rely on standard values like the meter, because everything in the universe is intertwined, and we can't say what a "meter" is in a universe which is totally different. People often ask something like: what would a universe be like where the speed of light is 1km/s. What does that question even mean? Does that mean a universe which is exactly just like ours, except that a meter is a much longer quantity? Or the same universe in which a second is defined as much longer? That's probably not what they meant when they asked the question, but there's no way to interpret what they did mean, since we can't exactly take a meter stick from our universe and use it to measure the other universe.

We can only make comparisons between prospective universes by taking ratios of the fundamental constants such that the units all cancel out, as in the case of the fine structure constant.

10. Apr 3, 2015

### Staff: Mentor

Hmm, then it is tricky to define how the boundary works like. I think the easiest way is to assume the electric charges of all particles change (in SI units).
For science fiction, it is certainly fine to say that the size of atoms changes. Regular bound states should exist for every value, but if they are too weak they will break up easily.
A variable planck constant would have weird effects I guess.

11. Apr 3, 2015

### Brian Sweet

In my case, I'm not referring to a hypothetical second universe, I'm trying to explore the possibility of a field or region within our own universe where the value of alpha is different. We already have data that suggests that the alpha constant has risen by a tiny fraction of a percent over the past six billion years, and even that it varies spatially across the universe. It's nothing significant at this point, but potentially interesting.

This is pretty much the crux of my question, and it might be something I just have to decide (it is science FICTION after all): working out what happens when something crosses into a region with an altered alpha constant, or what happens when the alpha constant changes over time in a given region. Definitely something to think about...

12. Apr 3, 2015

### Staff: Mentor

"Not significant" is the important point here. Thousands of measurements are done, and all of them have statistical fluctuations. Seeing some of them a bit away from the expected value is completely natural.