How do we know that physics works the same everywhere?

[TheSnack]

I'm very interested in many things, among them Astronomy. German TV broadcasts a very interesting show called Alpha Centauri, which deals with physics, especially astrophysics.
(If you can understand German, go to
http://www.br-online.de/alpha/centauri/archiv.html and watch some of the shows.)

The professor who does the show stated in one of them something to the effect of "physics works the same everywhere", something I have been told before. But never why?

So Physics-Dopers, why does physics work the same everywhere, and how do we know?

[muttrox]

We don't know for certain. It's an assumption. So far, it seems like a good one.

[CalMeacham]

Our observations are consistent with physics being the same everywhere. Until sometyhing satrongly suggests otherwise, it seems to be the most reasonable assumption. And it fits in with Occam's Razor.

A lot of interesting science fiction comes out of assuming that things are not the same everywhere. Read Poul Anderson's Brain Wave. Or Jack Chalker's "Well of Souls" novels. As far as I know, though, no one has seriously speculated on the laws of physics being different in different parts of space.


What would happen in the transition zones between regions where one set of rules held and where another set did?

[bryanmcc]

The fact that we can see stars billions of light-years away that appear to be following familiar laws of gravity, chemistry, and nuclear processes seems fairly indicitive that the laws are the same. I.e., the stuff we can see gazillions of miles away looks like its acting the same as stuff close by.

-b

[David Simmons]

Originally posted by TheSnack
I'm very interested in many things, among them Astronomy. German TV broadcasts a very interesting show called Alpha Centauri, which deals with physics, especially astrophysics.
(If you can understand German, go to
http://www.br-online.de/alpha/centauri/archiv.html and watch some of the shows.)

The professor who does the show stated in one of them something to the effect of "physics works the same everywhere", something I have been told before. But never why?

So Physics-Dopers, why does physics work the same everywhere, and how do we know?

Another poster mentioned that the light from astronomical objects from great distances appears to follow the same laws as in the laboratory here on earth.

An example is the spectrum of that light. In the laboratory, the light from hydrogen contains energy at a number of distinct wavelengths. This is the hydrogen spectrum. Light from the other galaxies contains energy at a number of distinct wavelengths. It turns out that if each wavength of that pattern from the galaxy is divided by the same number, say 1.35 as an example, all of the wavelengths from the galaxy are precisely the same as the wavelengths from hydrogen obtained in a laboratory here on earth. It is too much to assume that is a coincidence, because it happens over and over, with different dividing numbers, for galaxies all over the universe.

The explanation is that the galaxies are emitting the light from hydrogen and they are moving away from us so the wavelengths of the hydrogen spectrum is doppler shifted by the particular velocity of the different galaxies away from us. And the physics that produces the hydrogen spectrum here on earth is the same physics that produces the hydrogen spectrum in the distant galaxy.

[Urban Ranger]

If physics are not the same everywhere, Bad Things are very likely to happen. This Universe might not be stable or even exist.

Consider the speed of light. If the speed of light is faster somewhere and not so fast somewhere else, energy must be removed and added accordingly. How?

[smiling bandit]

Not neccessarily... the energy itself could simply be re-aligned at the point of difference. We're already postulating that physics would b different in different places, so why not?

[kniz]

Originally posted by smiling bandit
Not neccessarily... the energy itself could simply be re-aligned at the point of difference. We're already postulating that physics would b different in different places, so why not?

:confused: Ummm... CITE, please

[scotth]

About the only thing that is seriously being examined to work different far from here as close is gravity.

For the most part, as has been stated, every comparison of physical processes done in remote start match within our limits to measure them exactly the values we expect.

One of the solutions to the dark matter mystery that is being investigated is that gravity falls off at a lower than predicted rate when the gradient is very low. Technically, that doesn't mean that gravity works different somewhere else than here, it would really mean we don't understand gravity as completely as we thought. None the less, pretty interesting.

Status of that investigation, so far, a modification of Newtonian mechanics jives pretty good with observations, but so far it has been incompatible with relativity. This can mean a couple of things.

1) This theory is no good and there really is as much dark matter out there to account for galactic scale gravitational effects.
2) They just haven't hit upon the right way to do it yet.

Most people are leaning with the option 1. However, even the people most tightly in that camp think that this is a very good idea to persue. If for no other reason than to reliably rule it out. We are bound to learn something useful from it.

[JS Princeton]

The idea that the laws of physics are the same everywhere in the Universe is what precipitated the Newtonian Scientific Revolution. Before that people knew that apples fell to the ground and had been informed by Kepler and Galileo about the way in which heavenly bodies behaved, but until Newton, no one had really made the connection that these were consequences of the same physical processes.

Once Newton made that pronouncement, everything seemed to fall into place.

By the by, along with everywhere in the universe the laws of physics being the same also true is that for everywhen in the universe the laws are the same. This theory is falsifiable, so as soon as you discover some counter-evidence, give us a ring-a-ling.

[galrion]

I seem to recall an article in the New York Times a few months back that dealt with a similar topic. IIRC it theorized that the laws of physics towards the beginning of the universe were different and had changed over time to what they currently are. Does anyone else remember reading this? If they could change over time it could be that they are different in other places for some reason.

[scotth]

Originally posted by scotth
For the most part, as has been stated, every comparison of physical processes done in remote start match within our limits to measure them exactly the values we expect.


Wow, what was that supposed to mean.

I meant:

For the most part, every comparison of physical processes done in remote places match to the value we expect within the limits of our ability to measure. (In many instances, this is very precise indeed)

[muttrox]

Don't need a cite. It could be magic or the power of G-d. That's the whole OP.

[ZenBeam]

Consider the speed of light. If the speed of light is faster somewhere and not so fast somewhere else, energy must be removed and added accordingly. How?
This isn't a very satisfying argument. I could just as easily argue "Consider the speed of sound. If the speed of sound is faster somewhere and not so fast somewhere else, energy must be removed and added accordingly. How?".

People have looked into a time varying gravitational constant. I imagine spatially varying physics has been looked into also, if only to establish limits on how large of variation is possible without confilicting with observations. As others have mentioned, observations put pretty severe limits on possible variations.

[Squink]

The fine structure constant, involving e,h,c, appears to change (http://www.aip.org/enews/physnews/1999/split/pnu410-1.htm) over long time frames or astronomical distances.

[muttrox]

Most of these possibilities don't go to the OP. If the fine structure constant chagnes over time, it doesn't mean the laws of physics are different everywhere, it means our laws concerning the fine structure constant aren't general enough. If the exponent in gravitations equations is 1.999999993 instead of 2, it means our law is not accurate. It doesn't mean that gravity works differently in other places in the universe.

Consider pre-Einstein, you might think that the laws of physics didn't apply to Mercury. Post Einstein, you knew they did, but that our conception of those laws wasn't correct.

[TheSnack]

Thanks first of all for all the kind answers so far. Very interesting discussion! I suppose the main point of assuming physical processes to be the same everywhere is that if we assumed anything else, we might as well stop researching, since we wouldn't be able to establish the *other* physical processes. And if it works so far, that's fine.

I really have no reason to assume that the proposition is false, and I found Dave Simmons comments most helpful to answer my main question of "how do we know".

But thanks to all who responded!

[MercuryPenguin]

What about black holes? I seem to remember that normal physics don't apply inside of singularies.

[DrMatrix]

It depends upon what you mean by "normal physics". Relativity predicts black holes and the singularities at the center. Strange things happen inside the event horizon and some things take on unusual or undefined values at the singularity -- like the density being infinite. But this is all predicted by physics.

There is no "inside the singularity". The singularity is a point at the center of the event horizon.

[Chronos]

The physics that we know of breaks down at some point between the event horizon and the singularity of a black hole. That doesn't reflect on the laws of physics, though, it just reflects on our knowledge of those laws. Rest assured, the singularity of a black hole is happily following perfectly valid physical laws; we just don't know what those laws are, yet.

[AtomicDog]

Originally posted by muttrox
Don't need a cite. It could be magic or the power of G-d. That's the whole OP.

Then it is not physics or even science, and there's nothing to discuss.

[kniz]

Originally posted by muttrox
That's the whole OP.

Between which lines was it stated in the OP? :rolleyes:

[taggert]

Um, this assumes you know enough information about where you are and the forces acting on it. The laws are supposed to be the same, but that assume you have enough information. For example, if you watch water drain in Auckland or Oakland, you will see it swirl in different directions. If you know enough about your location, you can figure out why this is happening according to the laws of physics. That's why they call them laws of physics, not "suggestions of physics".

[pravnik]

Wait...isn't physics the science of discovery and not the sum total of knowledge gained to this point?

I think I need a definition of physics. Or better yet, science. Otherwise, saying physics works everywhere seems like a tautology, like saying "physics is physics".

[Shalmanese]

Originally posted by muttrox
Most of these possibilities don't go to the OP. If the fine structure constant chagnes over time, it doesn't mean the laws of physics are different everywhere, it means our laws concerning the fine structure constant aren't general enough. If the exponent in gravitations equations is 1.999999993 instead of 2, it means our law is not accurate. It doesn't mean that gravity works differently in other places in the universe.

Consider pre-Einstein, you might think that the laws of physics didn't apply to Mercury. Post Einstein, you knew they did, but that our conception of those laws wasn't correct.

Doesn't work that way, there is no such thing as a m^1.99993. The good thing about the fine structure constant is that it is dimensionless. It has the same value whether you are using microns, pounds and days or tons, micrograms and fortnights.

All the units cancel out in the end.

[pravnik]

I should add, I am not a physics guy. I got the beginners mind.

[smiling bandit]

Geez, I was half-joking, and half point out that at that point, you could just attribute it to the strange nature of the universe and go on about your business.

[muttrox]

Originally posted by Shalmanese


Doesn't work that way, there is no such thing as a m^1.99993. The good thing about the fine structure constant is that it is dimensionless.

Reread my post -- I used to examples, one referring to the fine structure constant, and one to gravitation, you are mixing the two.

[muttrox]

Originally posted by kniz


Between which lines was it stated in the OP? :rolleyes:

Ah, that would be the lines I apparently snorted before making snotty little posts. :smack:

What I was getting at ... The OP asked "How do we know?" We don't and we can't. For all we know, The Almighty has erected a miraculous barrier a light year out. Inside the barrier (us), he arranges it so we sense stuff that seems consistent with our laws of physics, but outside, it is really Heaven. Or Hell, or non-existent, or whatever.

I guess it was sort of nitpicky to point this out...

[Richard Pearse]

Originally posted by taggert
For example, if you watch water drain in Auckland or Oakland, you will see it swirl in different directions. If you know enough about your location, you can figure out why this is happening according to the laws of physics. That's why they call them laws of physics, not "suggestions of physics".

In the interests of stamping out ignorance, I should point out that you won't observe any consistant difference in draining water-swirl directions between Auckland and Oakland. The coriolis effect (which I assume you are alluding to) is not strong enough to make water drain in any particular direction.

Coriolis force (http://www.spartechsoftware.com/reeko/qanda.htm)



The Coriolis effect amounts to roughly 3/ 10,000,000 of the force of gravity, negligible to say the least in small events like toilet flushings. Other factors play a much larger part in drainage direction - small imperfections or shape distortions in the sink or tub, the micro movement of the water by outside disturbances such as the act of pouring the water in the drain (which, although undetectable by your eyes, may continue for several hours after the fact), and so on.

[AtomicDog]

Originally posted by pravnik
Wait...isn't physics the science of discovery and not the sum total of knowledge gained to this point?

I think I need a definition of physics. Or better yet, science. Otherwise, saying physics works everywhere seems like a tautology, like saying "physics is physics".


No, what I was saying is that once you add the supernatural (which is what muttrox was doing by factoring in magic and/or God), he takes the discussion outside of science's ability to analyze or predict. Magic isn't science.

[pravnik]

Sorry, AtomicDog, I didn't mean your post specifically. I guess I'm just saying that I don't understand the original statement by the german scientist in the OP when he says "physics is the same everywhere". I was thinking that physics is the tool physicists use to make observations about the universe, and not the universe itself. Sort of like saying, "you can't defeat logic, because you have to use logic to do it."

But I'm a layman and probably sticking my neck out too far, or publicly displaying my ignorance.

[pravnik]

Wait...I think I see. The same physics that works in the laboratory is in effect across the universe? If that's what's meant, :smack: I'm going to be quiet now.

[Chronos]

Um, why the pileup on smiling bandit? Urban Ranger pointed out that if, say, the speed of light changed in different places, that would violate the conservation of energy. smiling bandit just pointed out that that's not a problem, since we're considering the laws of physics changing anyway. That's a perfectly reasonable reply, and it stands on its own. How is a person supposed to find a cite for what the laws of physics would be if they weren't what they are?

[Liberal]

How is a person supposed to find a cite for what the laws of physics would be if they weren't what they are?That's easy. (http://soulinvitation.com/physicsofphi/PhysicsofPHI.html)

[Roadfood]

Originally posted by Urban Ranger
If physics are not the same everywhere, Bad Things are very likely to happen. This Universe might not be stable or even exist.

Consider the speed of light. If the speed of light is faster somewhere and not so fast somewhere else, energy must be removed and added accordingly. How?

Not if the law of conservation of energy is part of what's different.

I mean, you start out by saying, "If physics are not the same everywhere", and then you conclude with "energy must be removed and added accordingly." But that conclusion is only valid under currently accepted laws of physics. "If physics are not the same everywhere" then the law of conservation of energy might not hold, and therefore light might be able to change speed "at will", so to speak.

[VOW]

To Pravnik:

I think I need a definition of physics.

I saw this in a science lab at a college:

If it stinks, it's chemistry.
If it's green, it's biology.
If it doesn't work, it's physics.

Hope that helps.


~VOW