How do we know our laws of physics are correct?

  • #1
I was just curious to know, how do we know our laws of physics are correct? How do we know the laws about time or space aren't overruled (we say time flows forward, but how do we know that it cant skip back or flow backwards), because we just haven't seen it or can't perceive it?
 

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  • #2
Bandersnatch
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They make sufficiently accurate predictions to treat them as provisionally correct.
 
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  • #3
phyzguy
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Define "correct". We know our laws of physics are an accurate description of the universe because we have done a huge number of measurements and observations to validate them. Does your computer work? It was designed with our known laws of physics and wouldn't work if our physics models weren't reasonably accurate. How about your GPS tracker? Same comment. Do the space probes we launch toward the toward the planets actually arrive there? They wouldn't if our models were even slightly off. I could go on, but I think I've made my point.
 
  • #4
Define "correct". We know our laws of physics are an accurate description of the universe because we have done a huge number of measurements and observations to validate them. Does your computer work? It was designed with our known laws of physics and wouldn't work if our physics models weren't reasonably accurate. How about your GPS tracker? Same comment. Do the space probes we launch toward the toward the planets actually arrive there? They wouldn't if our models were even slightly off. I could go on, but I think I've made my point.

Well, by correct I mean, are they universally correct, and have they always been correct. Like can a law, let's pick a random one, the second law of thermodynamics, be overrules or proven wrong, yet we just haven't seen it been proven wrong yet. Apply this to bigger things like time itself, physicists say there is a flow to time, it always flows forward, how do we know that it can't flow backwards, or hell, skip forward or skip backwards, but we just haven't seen it yet?
 
  • #5
phyzguy
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Well, by correct I mean, are they universally correct, and have they always been correct. Like can a law, let's pick a random one, the second law of thermodynamics, be overrules or proven wrong, yet we just haven't seen it been proven wrong yet. Apply this to bigger things like time itself, physicists say there is a flow to time, it always flows forward, how do we know that it can't flow backwards, or hell, skip forward or skip backwards, but we just haven't seen it yet?

I would say we know that none of our laws of physics are "universally correct", if by this you mean that they apply exactly in every circumstance. All of our laws of physics have domains in which they are accurate to some verified level of accuracy, and domains in which they fail.
 
  • #6
Dale
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how do we know our laws of physics are correct?
We do experiments. If the result matches the prediction of the law then the law is correct in the experimentally tested domain.
 
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  • #7
I would say we know that none of our laws of physics are "universally correct", if by this you mean that they apply exactly in every circumstance. All of our laws of physics have domains in which they are accurate to some verified level of accuracy, and domains in which they fail.

When you say 'domains in where they fail' are you referring to extreme domains, like inside a black hole and stuff? But really what I meant was, how do we know laws that we assume are correct in a domain are just incorrect? Like how can we be sure time always flows forward? (I use time as it is an easy example and we experience it every day).
 
  • #8
phyzguy
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When you say 'domains in where they fail' are you referring to extreme domains, like inside a black hole and stuff? But really what I meant was, how do we know laws that we assume are correct in a domain are just incorrect? Like how can we be sure time always flows forward? (I use time as it is an easy example and we experience it every day).

I'm not sure what you are asking. I've never experienced time flowing backwards, and I don't think you or anyone else has either. If you are asking, "How do we know that are laws of physics that are valid today will still be valid in the future?", the answer is that we don't. It is a basic postulate of physics that the same laws of physics that we experience here on Earth at this time are valid throughout the universe and for all times. This postulate has been extraordinarily successful at describing what we see.
 
  • #9
I'm not sure what you are asking. I've never experienced time flowing backwards, and I don't think you or anyone else has either. If you are asking, "How do we know that are laws of physics that are valid today will still be valid in the future?", the answer is that we don't. It is a basic postulate of physics that the same laws of physics that we experience here on Earth at this time are valid throughout the universe and for all times. This postulate has been extraordinarily successful at describing what we see.
Yeah, that's what I meant, will the laws we see as correct today, be correct in the future? Like, Newtonian physics was proven wrong by Einstein. So, how do we know the same won't happen to our laws now?
 
  • #10
phyzguy
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Yeah, that's what I meant, will the laws we see as correct today, be correct in the future? Like, Newtonian physics was proven wrong by Einstein.

Newtonian physics was not "proven wrong". It is an excellent model of our universe within its domain of applicability and is used to great effect by millions of people every day. You should read the following insights article:

https://www.physicsforums.com/insights/classical-physics-is-wrong-fallacy/

So, how do we know the same won't happen to our laws now?

Our current laws of physics will almost certainly be improved upon in the future. We certainly expect (and hope!) that there will be better models in the future with greater accuracy and larger regimes of applicability.
 
  • #11
Newtonian physics was not "proven wrong". It is an excellent model of our universe within its domain of applicability and is used to great effect by millions of people every day. You should read the following insights article:

https://www.physicsforums.com/insights/classical-physics-is-wrong-fallacy/



Our current laws of physics will almost certainly be improved upon in the future. We certainly expect (and hope!) that there will be better models in the future with greater accuracy and larger regimes of applicability.

So basically, our laws of physics which we observe to be correct can't be wrong, just proved upon in the future. Its not like the second law of thermodynamics can suddenly be proven wrong in the future, but it could be improved from what it is. Would I be correct?
 
  • #13
Vanadium 50
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How do we know reindeer can't fly?
 
  • #15
jbriggs444
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So we can safely say all our current laws are correct?
What kind of confidence are you looking for? We bet our lives every day on things that we know with a good deal less reliability. How do you know that the brakes in your car still work today?

Our laws of physics are well tested within the regimes available for experimentation. That is as good as it gets.
 
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  • #16
Dale
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Like, Newtonian physics was proven wrong by Einstein. So, how do we know the same won't happen to our laws now?
Newtonian physics was not proven wrong by Einstein. Newtonian physics is part of relativity, specifically the v<<c part. So relativity can not prove it wrong.

All of the centuries of experimental evidence supporting Newtonian physics still holds in the respective domains of the experiments. That is why Newtonian physics is still taught in school. Newtonian physics is right, in the Newtonian domain.

So we can safely say all our current laws are correct?
Yes, they are all correct in the domain where they have been experimentally validated.

At this point your question has been answered repeatedly.
 
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  • #17
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If you cannot see the sun due to cloud, does it prove that its not there?

There is nothing like absolute truth.

You may say that if a car on ground in earth accelerates in forward direction, it will go back. You may develop the math as well. Stretch the fact to n dimensions or something. But in this space/domain will any car follow such law? At least in any space we know?

Any other observer will see that the car will always go forward. Hence your equation does not match with experiment thus incorrect.

This establishes that physics is RELATIVE, physical laws are developed for THIS DIMENSION only(we cannot develop physical equations without knowing data from other simension) EXPERIMENTS/OBSERVATIONS MUST MATCH EQUATIONS developed for a particular dimension.
Together with all DATA we prove that the laws are Correct.

Try this, if a is a natural number then a>0. Prove there exists an a<0.No one knowns the complete N set. There can be!

If you can't generate any counter example then it is implied that if a is in N then it is always greater 0.

Same for Physics, generate enough data/evidence to show that physical equations are incorrect,if you cannot then it is implied that laws are correct and you are wrong.
 
  • #18
sophiecentaur
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So we can safely say all our current laws are correct?
You are just re-stating your OP, slightly differently. Is there any reason, other than 'mischief' that is keeping you on this course? You are using the word "correct" in an imprecise way and there is no answer until you say exactly what you mean by it. In the terms of "Science", the laws are 'correct'. In your terms (as yet unspecified) they could be 'incorrect'. But what does that say about your terms?
If you have a problem with the scientific attitude then that is a separate issue. Many people feel excluded from the club of Science because they find the ultra careful and formal way the Laws are stated is too hard to follow. That's a personal problem for them and not a problem for 'Science'.
 
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  • #19
You are just re-stating your OP, slightly differently. Is there any reason, eight than 'mischief' that is keeping you on this course? You are using the word "correct" in an imprecise way and there is no answer until you say exactly what you mean by it. In the terms of "Science", the laws are 'correct'. In your terms (as yet unspecified) they could be 'incorrect'. But what does that say about your terms?
If you have a problem with the scientific attitude then that is a separate issue. Many people feel excluded from the club of Science because they find the ultra careful and formal way the Laws are stated is too hard to follow. That's a personal problem for them and not a problem for 'Science'.
Sorry, I meant correct as in, are they just correct for now, for what we know, and will they be proven incorrect in future when we get more knowledge, like how Newtonian physics, I thought was incorrect, but I was proven wrong, it was just improved upon.
 
  • #20
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Science because they find the ultra careful and formal way the Laws

Laws/Theorems must be precise, concise, independent of what is being defined and formal.

Science always has been and always will be a dense network of closely related ideas made simple through laws and equations.
This is the most simplification we can achieve and we should.

You cannot spell CAT without knowing what is C, A, T and how to make meaningful words with it.
 
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  • #21
sophiecentaur
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will they be proven incorrect
Now you have not identified what you mean by 'incorrect' either. If you're asking "will aeroplanes fall out of the sky and will computers stop working?" then clearly the answer is "no".
But no true Scientist will be surprised (or resentful) if a more comprehensive model for fundamental particles turns up.
I still cannot decide what your actual point is. If someone finds a phenomenon that can only be explained by time reversal then the Law about Time's Arrow will need to be modified but it won't affect how familiar things work. And no example has been found yet - which is very relevant to this discussion. :wink:
Perhaps you were looking for more Authority behind the so called Laws. That may be because the word "Law" was introduced when the way things behave was generally attributed to the agency of a divine being. The word is a legacy from earlier times and belief systems. A divine being could, presumably, change their mind and that could lead to planes falling out of the sky etc one day!!!!
 
  • #22
CWatters
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Stephen Hawking's book The Grand Design covers the OPs question. I'm about three quarters of the way through it and it's very readable.
 
  • #23
Stephen Hawking's book The Grand Design covers the OPs question. I'm about three quarters of the way through it and it's very readable.

What is stated in the book exactly?
 
  • #24
CWatters
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The first few chapters attempts to answer such questions. There isnt a yes/no answer. Full list of chapter headings..

1. The mystery of being
2. The rule of law
3. What is reality
4. Alternative histories
5. Theory of everything
6. Choosing our universe
7. The apparent miracle
8. The grand design

I'm sure there are full reviews on the web.

For me the most interesting thing so far was the experiment that appears to prove we can change the past (delayed choice double slit experiment).
 
  • #25
phyzguy
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It's a long slog, but if you really want an understanding of our physics models, their limitations, and how they relate to mathematics, I highly recommend Roger Penrose's "The Road to Reality".
 
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  • #26
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Rather than say, "Correct" it would be more precise to say that our current laws accurately describe physical phenomenon to an acceptable level of predictability. If I drop a rock anywhere on the Earth's surface, I have an expectation it will fall at an accelerated rate of close to 9.8 meters per second per second. I have a reasonable expectation that the speed of light between the Earth and the moon is going to be the same speed in a vacuum at any place 14 billion light years from here.

As said above, they are laws because they are repeatable and have been measured with the same results for decades, if not hundreds of years, and astronomical observations show them to be accurate up to billions of years in the past. That doesn't mean that we can't increase the accuracy of our measurements to additional decimal places. It doesn't mean that we can't discover at some later time that a single value constant we've been using might not be made up of multiple components. And that doesn't mean that we can't discover a better formula to describe a phenomenon than a current law. Newton's laws work just fine for me in everyday life. I don't need the level of precision to find out what fraction of a second I slow down driving to work at 55 mph. But that would be relevant if I were traveling to another star system at greater than half the speed of light, so I'd need relativistic laws to better describe things. Doesn't mean I can't use Newtonian mechanics to plan for an interstellar voyage; it's just the margin of error is a lot larger because the tool isn't really appropriate for that task.
 
  • #27
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I think Feynman's chess analogy would get to the heart of the OP's question:



If you don't want to watch the video:
Science is like observing a chess game when we don't know the rules. We deduce the rules by watching the game being played, for example that a given bishop is always on the same color square. This law then becomes refined when we learn that bishops only move diagonally, which explains the previous law, but in a more complete way. The previous law that bishops stay on the same color square is not wrong, just incomplete. Our collection of laws based on observation may not match the "official" (or "correct" as the OP is asking) rule book* for chess, but it would allow us to understand how it is played. In that use of the word "correct" the answer is that we can't know if it is correct. I think this is what the OP is driving at.

*Also see Paul Erdos' "straight from the book".
 
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  • #28
pinball1970
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It's a long slog, but if you really want an understanding of our physics models, their limitations, and how they relate to mathematics, I highly recommend Roger Penrose's "The Road to Reality".

Great book, my son pinched my copy when I was a third into it so I had not really got into the meaty stuff- I have to replace it.
 
  • #29
One comment I saw that had a big appeal to me:

"Science isn't the process of replacing wrong theories with right ones. Science is the process of replacing wrong theories with ones that are more subtly wrong."


Our process for science -- at least the well defined ones like physics -- makes it unlikely to have a total contradiction to a present rules. However I don't see any reason to doubt that we will replace theories with ones that need another decimal point or six to see the difference.

To me the more interesting question isn't "Are they correct" but rather "Are they complete?" And the answer to that is almost certainly "No"

Dark matter?

Shadow matter?

Exotic matter?

Dark Energy?

Resolution of Quantum Mechanics and General Relativity?
 
  • #30
Dale
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Science is the process of replacing wrong theories with ones that are more subtly wrong.
That is too pessimistic for me. How about “Science is the process of taking valid theories and extending them to new experimental domains”. That is both more positive and more accurate. After all, can you really say that relativity replaced Newtonian mechanics when Newtonian mechanics is still used more often? Isn’t it more accurate to say that it extended it?
 
  • #31
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Actually, we had a huge revolution recently, that concluded that the "Law of Conservation of Mass/Energy" is incorrect. The violation is that the universe seems to be expanding at an increasing rate. There is currently no way to reconcile this with the conservation law. An invisible source of mass/energy might work. But currently the understanding is that the expansion of the universe will increase its mass/energy by huge amounts--another few universes of mass wouldn't be enough to balance things. (The vacuum energy is more than enough.)

The second result is recent and much more subtle. https://physicsworld.com/a/dark-energy-emerges-when-energy-conservation-is-violated/ A QM model where energy is not conserved allows for the energy "lost" on a small scale to create the Cosmological Constant, even though the energy conservation violations are difficult or impossible to see on even a solar system scale.

Will a "Theory of Everything" eventually have a conservation law? Don't know. My guess is that just like adding mass as a result of nuclear physics, the true conservation law will have at least one more term.
 
  • #32
Drakkith
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Actually, we had a huge revolution recently, that concluded that the "Law of Conservation of Mass/Energy" is incorrect. The violation is that the universe seems to be expanding at an increasing rate. There is currently no way to reconcile this with the conservation law.

I'm not convinced. My understanding was that the issue simply wasn't settled yet and I haven't heard anything about a consensus on the subject.

The second result is recent and much more subtle. https://physicsworld.com/a/dark-energy-emerges-when-energy-conservation-is-violated/ A QM model where energy is not conserved allows for the energy "lost" on a small scale to create the Cosmological Constant, even though the energy conservation violations are difficult or impossible to see on even a solar system scale.

Note that this model is very speculative and currently has little to support it over other models.
 
  • #33
Dale
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Actually, we had a huge revolution recently, that concluded that the "Law of Conservation of Mass/Energy" is incorrect. The violation is that the universe seems to be expanding at an increasing rate.
Conservation of energy is valid at less than cosmological scales, as centuries of experimental evidence shows. None of the cosmological results change the non-cosmological evidence validating the conservation of energy.
 
  • #34
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There's a famous syllogism by Bertrand Russell:

Bread is a stone
Stones are nourishing
Therefore bread is nourishing

The syllogism is supposed to illustrate that a theory can be valid even though the premises themselves are false. So, the postulates of a theory may lead to predictions that are borne out by experiment even if the postulates are not 'correct' (in the universal way the OP refers to). There is no way to tell whether a theory is universally correct.
 
  • #35
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Science evolves. That's what makes it interesting after all. If we knew all the laws from the start of written history (some around 10000BC) it would just be so boring, there would be no evolution.

The evolution of science involves (in my opinion) taking laws that are approximately correct in some domains (the error of approximation is so small in these domains that cannot be experimentally tested, for example Galileo transformations are correct for all domains with velocities <5% of speed of light) and extending them to new domains where the error of approximation is much bigger. So we have to evolve the previous known laws in order to make the error of approximation again small in the new domains. But we cant be sure whether the newly evolved laws are again a very good approximation or they are the absolute correct laws of the universe, the newly evolved laws maybe someday will have to evolve again to match new experimental data from new domains.
 
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