# As the Universe is expanding

....why aren't the laws of physics changing ?

Gravity for example works on a formula dealing with the inverse square of distances. If those distances are changing, why isn't the law of gravity changing ? Or indeed everything.

Anybody have a simple answer ? Ta.

## Answers and Replies

If they were constantly changing, they wouldn't be very good 'laws' now would they?

The distances aren't changing - at least not enough to make a difference.

Regardless, why do the laws need to change? They allow for changing distances and given observations agree with them, there's nothing wrong with them.

Distance changes, gravity changes - it's only if the distance changed but gravity didn't that you'd need to amend the law.

russ_watters
Mentor
When the number you plug into a formula changes, that doesn't imply that the formula is changing.

Thanks, I kinda understand what you're saying.

But I'm still puzzled. Is it true that our 'laws' are intrinsically linked to the physical properties of what we call 'space-time' ?

So if you 'fast forward' the universe another 14 billion odd years to a point where (presumably) it will be much 'larger' and less dense.. will the same laws still hold ? Seeing as the 'fabric' they are (again presumably) based on will have radically changed ?

Basically, do the same laws still hold no matter what macroscopic scale is involved ? And can we prove it one way or the other ?

Ah, this a question about the variability of Alpha isn't it ?

So I'll take it as a 'we don't know yet'. Cheers.

It's amazing how many people come here, ask a question and then ignore the answers given

True, but then if Alpha does vary (which seems to be in doubt at the moment) then the standard answers given are pretty moot in the first place aren't they ?

How hard is it to say 'we don't actually know for sure' or 'it's under investigation' ?

And why do people get so worked up about it. Sheesh.

Is it true that our 'laws' are intrinsically linked to the physical properties of what we call 'space-time' ?

They are based on observations. The laws agree with our observations.
So if you 'fast forward' the universe another 14 billion odd years to a point where (presumably) it will be much 'larger' and less dense.. will the same laws still hold ? Seeing as the 'fabric' they are (again presumably) based on will have radically changed ?

I don't see why not. It wouldn't be difficult to simulate.
Basically, do the same laws still hold no matter what macroscopic scale is involved ? And can we prove it one way or the other ?

As far as current observations go, yes.
True, but then if Alpha does vary (which seems to be in doubt at the moment) then the standard answers given are pretty moot in the first place aren't they ?

How hard is it to say 'we don't actually know for sure' or 'it's under investigation' ?

And why do people get so worked up about it. Sheesh.

Your initial question has absolutely nothing to do with this. You asked why the laws aren't changing, the answers were given.

Current observations agree with the laws as they stand. This answers your question.

I tried looking up the variation in alpha and couldn't find anything useful - can you cite a source for it so I can read?

Sure, I had no idea btw that this was some sort of point of debate when I asked the question ( I am not any sort of physicist, it just seemed like a reasonable question from an observers point of view).

Here is an article on some research which seems to cast doubt on the invariability of Alpha- http://www.economist.com/node/16930866?story_id=16930866&fsrc=nwl

The reason I asked is because as the article points out, the implications would no doubt be interesting.

BruceW
Homework Helper
Interesting article. In my opinion, a law of physics is always obeyed, so if it was found that the fine structure constant varied, then I would say that the fine structure constant is technically a parameter, not a constant.

For example:
Two of the basic forces (electromagnetism and the weak nuclear force) were combined as one force when the universe was much younger. So in some sense you could say the laws have changed. But on the other hand, you could say that in the conditions of the early universe, those two forces acted the same.

The fine structure constant is not a law, it is a constant. Changing the fundamental constants WILL change the physics.

But you asked do the laws change, and the answer, is clearly no.

The problem with saying something is finely tuned is that every measurement of every quantity is APPROXIMATE. So we already know that there is a +- associated with our measurement. Therefore according to present knowledge it clearly can be varied by this +- amount and still not affect anything.

So you can change the fine structure constant, albeit by not very much, and nothing will happen to our universe.

The laws of physics are universal...thats y they are LAWS...if they wud have changed with time then the laws are actually of no news...on the other hand as far gravity is cocerned...we still have not understood this force completely...man scientists are working on the so called MOND theory which does change the law gravity wen u take into account large distances...but then this is again just a hypothesis without any concrete observational support...so the case may be that gravity does change with distance and may be with time too...

A law is just a theory.

It just happens that at the time they were made, terminology called them laws.

A law is just a theory.

It just happens that at the time they were made, terminology called them laws.

A law is a law, a theory is a theory. A theory will never become a law, a law will never become a theory.

To quote DrGreg who gives a nice explanation:
You have a misunderstanding over the use of the terms "law" and "theory". In physics, they mean pretty much the same thing, and it's just an artefact of history that we refer to Newton's "laws" but Einstein's "theories". Both are mathematical models of reality, but Einstein's model works better, in more diverse situations, than Newton's. Einstein's theory therefore supersedes Newton's so-called "laws" which are now seen as approximations which work well in many situations but break down when you push them too far.

And I'll say he is wrong.

A scientific law is a observation that always occurs when under the same conditions. That's where you have Ohm's Law, Newton's Law, Hooke's Law, Snell's Law... They don't try to explain anything, they just state what happens.

A scientific theory tries to understand these laws and give an explanation for why they happen.

Neither supercedes each other.

From dictionary.com:
Scientific Law: a phenomenon of nature that has been proven to invariably occur whenever certain conditions exist or are met; also, a formal statement about such a phenomenon

Scientific Theory: a theory that explains scientific observations

Just google it. Everywhere gives this definition of scientific law and observation.

Fair enough, good show old chap.

....why aren't the laws of physics changing ?

Gravity for example works on a formula dealing with the inverse square of distances. If those distances are changing, why isn't the law of gravity changing ? Or indeed everything.

Anybody have a simple answer ? Ta.

Dark Matter and Dark Energy are the gap fillers, Gravity does not need other celestial objects near by to function the same because of those two forces.

The fine structure constant is not a law, it is a constant. Changing the fundamental constants WILL change the physics.

But you asked do the laws change, and the answer, is clearly no.

The problem with saying something is finely tuned is that every measurement of every quantity is APPROXIMATE. So we already know that there is a +- associated with our measurement. Therefore according to present knowledge it clearly can be varied by this +- amount and still not affect anything.

So you can change the fine structure constant, albeit by not very much, and nothing will happen to our universe.

Thank you. That makes more sense.

So, in theory, would it be possible to have a different universe with the same physical laws but containing vastly more matter/energy ? Say with ten times the matter/energy density of our Universe ?

I'm not asking if life would be possible, just if such a vastly more dense universe would be possible? And would it still follow the same 'laws' (assuming all the fundamental forces acted on it in a similar matter) ?

I'm just trying to establish a line of reasoning here. And this is a fundamental point.