I Topic about physics axioms, theory, laws etc..

[Dale]

No. If you throw coin many times, it will lands on both sides.

That would be a different theory.

Staying with my theory that the coin always lands “tails”, how many throws would you require to show “tails” before you would consider my theory “proven”?

Clearly 1 experiment with “tails” did not satisfy you. How about if it landed “tails” 10 times, then would you say my theory was “proven”? How about 100? 1000? What is the exact minimum number of “tails” that you would require to “prove” my theory?

 

[jbriggs444]

No. If you throw coin many times, it will lands on both sides.

Not necessarily. The probability depends on how many times you throw.

If you measure torque, it will show the result T=Fxr absolutely every time..(if we neglect devices measurement error).
If the formula is not correct, bridges, houses, etc. would collapse on a regular basis.

That is not quite correct either. Torque, by itself is just a number. It has no physical consequences. If we have a force $\vec{F}$ applied to a moment arm of $\vec{r}$ then that force results in a torque $\tau$ given by $\vec{r} \times \vec{F}$. That is true. By definition.

We need to tie that number ($\tau$) to something physical if we are going to make a prediction.

We can do that. We can start by defining another number, angular momentum ($L$), as the sum of $\vec{r} \times \vec{p}$ across the incremental mass elements that make up an object.

We can can next assert that $\sum \tau = \frac{dL}{dt}$

Now for a continuously unmoving object we are in a position to predict that the sum of the torques on that object is zero. And for an object subject to a net torque, we can predict its angular acceleration.

Though we might need some more definitional axioms for "rigid object", "angular velocity" and "angular acceleration"

 

[user079622]

That would be a different theory.

Staying with my theory that the coin always lands “tails”, how many throws would you require to show “tails” before you would consider my theory “proven”?

Clearly 1 experiment with “tails” did not satisfy you. How about if it landed “tails” 10 times, then would you say my theory was “proven”? How about 100? 1000? What is the exact minimum number of “tails” that you would require to “prove” my theory?

Neither once, because I know from logic/experience that this experiment doesn't make sense. Experiment will shows that theory is wrong in first few throws.

So everything in Physics=maybe, I am disappointed by that fact, disappointed that everything what we learn is maybe wrong.

 

[jbriggs444]

I am disappointed by that fact, disappointed that everything what we learn is maybe wrong.

Welcome to the real world.

 

[fresh_42]

So everything in Physics=maybe, I am disappointed by that fact, disappointed that everything what we learn is maybe wrong.

I am totally satisfied with Newton when I start my car, although I know he was wrong.

 

[user079622]

Welcome to the real world.

Not necessarily. The probability depends on how many times you throw.

If coin is thrown every time with same initial condition(ex. machine) it will land always on same side. Determinism can't be fooled. Indeed from my pure logic, randomness can't exist, just appear to us to exist.(In my beliefs even in atomic world, now when we conclude that physics doesn't have to be correct, no one can't prove me that my belief is 100% wrong.)

I am totally satisfied with Newton when I start my car, although I know he was wrong.

Even if he was wrong, considering what he had at his disposal at the time, he discovered great things.
It seems Einstein is also wrong at atomic level.

 

[jbriggs444]

Indeed from my pure logic, randomness can't exist

You might be disheartened to learn that plain old Newtonian mechanics is not deterministic in all cases. John Baez points out some problems with the continuum model here.

 

[user079622]

You might be disheartened to learn that plain old Newtonian mechanics is not deterministic in all cases. John Baez points out some problems with the continuum model here.

Now I can always say, maybe he is wrong..

 

[Dale]

Neither once, because I know from logic/experience that this experiment doesn't make sense. Experiment will shows that theory is wrong in first few throws.

OK.

So now let’s change it. Now let’s suppose that we have just encountered a flubnubitz for the first time. Like a coin a flubnubitz has two sides but unlike a coin it feels somewhat asymmetrical. We accidentally drop it and it lands with a “tails”. I drop it 9 more times and each time it lands “tails”.

Based on my initial experience I make a theory that unlike coins, a flubnubitz always lands “tails”.

With my 10 experiments all showing “tails”, have I proved my theory? What about with 100 or 1000?

 

[user079622]

Experiment. A good summary is section 3 in the Experimental Basis of Special Relativity page.

Did Dayton Miller conduct Michelson-Morley experiments in 1930's, and find some difference in light speeds, and prove speed of light depend of source speed?
Is this true?
at 8:20

So now let’s change it. Now let’s suppose that we have just encountered a flubnubitz for the first time. Like a coin a flubnubitz has two sides but unlike a coin it feels somewhat asymmetrical. We accidentally drop it and it lands with a “tails”. I drop it 9 more times and each time it lands “tails”.

Based on my initial experience I make a theory that unlike coins, a flubnubitz always lands “tails”.

With my 10 experiments all showing “tails”, have I proved my theory? What about with 100 or 1000?

For same initial condition, object will land always on same side.
Yes, if you've never seen black swan, it doesn't mean it doesn't exist.

 

[jbriggs444]

Did Dayton Miller conduct Michelson-Morley experiments in 1930's, and find some difference in light speeds, and prove speed of light depend of source speed?

No. He did experiments. They were flawed. The results could not be reproduced.

A quick trip to Google pulls up this article.

Observations involving binary star systems put the kibosh on theories where light speed depends on the speed of the source.

 

[Ibix]

Did Dayton Miller conduct Michelson-Morley experiments in 1930's, and find some difference in light speeds, and prove speed of light depend of source speed?

He did conduct experiments and he did think he had found something like you say, but he was mistaken. See https://www.arxiv.org/abs/physics/0608238, which is linked from the excellent "Experimental basis of SR FAQ" that's stickied in the Relativity forum. From the abstract: In short, this is every experimenter's nightmare: [Miller] was unknowingly looking at statistically insignificant patterns in his systematic drift that mimicked the appearance of a real signal.

 

[user079622]

No. He did experiments. They were flawed. The results could not be reproduced.

A quick trip to Google pulls up this article.

Observations involving binary star systems put the kibosh on theories where light speed depends on the speed of the source.

Today with modern devices is confirmed that light dont depend on source speed?

In Michelson-Morley experiment what speed they use for Earth? earth is not moving just around sun, galaxy is also moving, etc etc so if aether is absolute stationary we dont know what is earth absolute speed?

 

[Dale]

Yes, if you've never seen black swan, it doesn't mean it doesn't exist.

And fundamentally that is why the scientific method can never be said to “prove” a theory true. It is an inherent limitation of the scientific method.

So everything in Physics=maybe, I am disappointed by that fact

One thing that may help you to be less disappointed is to know is that there are different degrees of maybe.

Suppose now that we have two competing theories of flubnubitz. My theory that they always come up "tails" and Bob's theory that they come up "tails" randomly with a 50% probability. After gathering 100 experimental trials and finding that they all were "tails" I cannot say that either theory is "proved". Maybe my theory is correct, but maybe Bob's theory is correct and we were just unlucky the first 100 trials. But the maybe for my theory is a lot more believable than the maybe for Bob's theory.

So although we have not "proven" either theory, we have learned about both theories. We have not eliminated uncertainty entirely, but we have reduced it substantially.

 

[Ibix]

In Michelson-Morley experiment what speed they use for Earth?

They didn't use a speed. They aimed to measure the change in speed relative to the ether over a year, and found a null result.

 

[fresh_42]

From the German Wikipedia:

The first proof that the speed of light is finite was achieved by the Danish astronomer Ole Rømer in 1676. He found seasonally fluctuating travel times for clock signals from Jupiter (entry of Jupiter's moon Io into Jupiter's shadow), while on this side, the Earth's rotation served as a stable time reference. He determined a travel time of 22 minutes for the diameter of the Earth's orbit. The correct value is shorter (16 minutes 38 seconds). Since Rømer did not know the diameter of the Earth's orbit, he could not provide a value for the speed of light. Christiaan Huygens did this two years later. He related Rømer's travel time to the diameter of the Earth's orbit around the Sun, which Cassini had accidentally determined almost correctly in 1673 (see solar parallax for the gradual improvement of this value), and arrived at a speed of light of 213,000 km/s.

The first earthly determination of the speed of light was achieved by Armand Fizeau using the gear method. In 1849, he sent light through a rotating gear to a mirror several kilometers away, which reflected it back through the gear. Depending on the speed of the gear, the reflected light, which had passed through a gap in the gear on its way there, either falls on a tooth or passes through a gap again, and only then can it be seen. Fizeau's value was 5% too high.

 

[A.T.]

So everything in Physics=maybe, I am disappointed by that fact,

If you want certainty, try religion.

 

[Jaime Rudas]

I always thought that everything we learned in school of physics is 100% correct. Now I see that math and physics is very different in that aspect..
Can I say math is absolute truth, physics is just best current approximation for reality?

Yes, in the sense that we can differentiate between two types of truth: logical truth and factual truth. In a given logical system, statements are considered true if, using the rules of the system, they can be deduced from the axioms and postulates. Factual truth consists of the complete correspondence between reality and our idea of it. Thus, it is possible to establish the truth of a logical statement, but, in general, it isn't possible to establish the truth of a factual statement (although it is possible to establish its falsity).

 

[Jaime Rudas]

Is this axioms?

• The laws of physics are the same in all inertial frames.
• The speed of light in vacuum is constant in all inertial frames.

In one sense, they are postulates of physical theories, which are logical systems. In another sense, they are factual hypotheses that can be verified.

 

[Herman Trivilino]

Is this axioms?

• The laws of physics are the same in all inertial frames.
• The speed of light in vacuum is constant in all inertial frames.

Einstein constructed his special theory of relativity in 1905 using these as postulates. His goal was to show the consequences of accepting these two experimental behaviors.

So, they are postulates subject to experimental and observational verification. Einstein himself was interested in any experimental endeavors that might show that the speed of light from a distant star showed any dependence on the motion of the star. He knew that if the postulres were in any way invalid it would mean his entire theory would have to be modified.

 

[dextercioby]

Building a physical theory - the job of a theoretical physicist - requires two things to start: a set of definitions and a set of postulates, i.e. statements that cannot be directly logically proven, but can and must be used to derive results in the form of theorems/statements. We say that a theory of physics has two different but equivalent formulations, if the postulates of one formulation can be thorems in the other and viceversa.

Here's a question: if we superficially say that the theory of special relativity (as known today after about 120 years) is summarized by the two postulates:

• The laws of physics are the same in all inertial frames.
• The speed of light in vacuum is constant in all inertial frames.

what is the set of definitions necessary in a book/university course to be explicitely formulated before stating these postulates, for these two statements (together with the definitions I am asking about) to "begin producing results" such as the proposition: "the length of an object is not absolute, but inertial frame-dependent"?

 

[user079622]

He did conduct experiments and he did think he had found something like you say, but he was mistaken. See https://www.arxiv.org/abs/physics/0608238, which is linked from the excellent "Experimental basis of SR FAQ" that's stickied in the Relativity forum. From the abstract: In short, this is every experimenter's nightmare: [Miller] was unknowingly looking at statistically insignificant patterns in his systematic drift that mimicked the appearance of a real signal.

Sound:
1. If sound source move toward me, I measure higher frequency and same speed of sound.
2. If I move toward sound source, I measure higher frequency and higher speed of sound(relative to me, even sound speed relative to medium stay constant).

Light (vacuum):
3. If light source move toward me, I measure higher frequency and speed c .
4. If I move toward light source, I measure higher frequency and speed c

Why in 4. speed is not higher(like in wave 2.)? Any logical explanation why this happen?

"If light speed depended on observer velocity, causality would break down"
Why would causality brake down, if light wave from some event didn't come to your eye retina, that doesn't mean that this event didn't happen?What has EM wave with causality?

 

[Ibix]

Why in 4. speed is not higher(like in wave 2.)?

Depends what you mean. Why there is a speed that is the same in all frames is not known. It just appears to be how the universe works - Einstein postulated it, worked out the implications, and found that they matched existing experimental results. However, you can answer why light travels at the invariant speed, which is because it is massless.

"If light speed depended on observer velocity, causality would break down"

On it's own that makes no sense. Please link to the context of that claim.

 

[user079622]

On it's own that makes no sense. Please link to the context of that claim.

There is tone of content if speed of light is not constant it will brake causality.
EM wave don't have nothing to do with causality.
Why would speed of causality be speed of light?

 

[Ibix]

There is tone of content if speed of light is not constant it will brake causality.

Please link to some, then. The video you posted looks to be about the tachyonic anti-telephone, which shows how faster than light communication allows paradoxes assuming special relativity is true - that is, assuming the speed of light is invariant for all inertial observers.

Why would speed of causality be speed of light?

You have this the wrong way round. A direct consequence of assuming that there is a finite invariant speed is that nothing can travel faster than that without causal paradoxes (which the tachyonic anti-telephone thought experiment shows). Note that I did not mention light at all. Separately, you can ask why light travels at that invariant speed, which I answered in my last post: because it's massless.

It's unfortunate that the invariant speed is still called the speed of light, because that's really an artefact of the historical development of the theory. It's perfectly possible to write down the theory of a universe in which light does not travel at the invariant speed - the photon ends up having mass and can be stopped like any other particle, and causality is unaffected. In fact, that theory is used as a test theory to test our belief that the photon is massless (its mass is indistinguishable from 0kg to 50-something decimal places, IIRC).

 

[Herman Trivilino]

Why in 4. speed is not higher(like in wave 2.)? Any logical explanation why this happen?

Because in 4 the speed is less than c.

Here's a geometric analogy. If you stack wedges 1 and 2 (see figure) you can make the slope of the upper surface of the stack steeper. (And you can continue this practice if you add another wedge 3.) If you keep adding wedges the upper surface is vertical, but you can't increase the slope further by adding additional wedges.

Why does adding wedges not make the slope get steeper when the upper surface is vertical (like it does when the slope of the upper surface is not vertical)? Any logical explanation why this happens?

 

[Herman Trivilino]

Why would speed of causality be speed of light?

This question is better phrased as why is there a fastest speed? And why is that the speed of causality and also the speed of light?

 

[hutchphd]

e, I am disappointed by that fact, disappointed that everything what we learn is maybe wrong.

You do not understand the unique genius of the scientific method, and therefore you do not understand anything much about physics. The fact that every fact we learn may be wrong is the entire point and power of hard science. It redounds to social as well as technological realms. Your disappointment illustrates this insufficient understanding which, alas, is widespread even among the "educated". Physics has little to do with a certain pile of facts.

 

[Herman Trivilino]

The fact that every fact we learn may be wrong is the entire point and power of hard science. It redounds to social as well as technological realms.

Failure to understand this is perhaps the greatest shortcoming of our society.

 

[user079622]

However, you can answer why light travels at the invariant speed, which is because it is massless.

Yes that make sense.
But why this is speed of causality?
Event happen before observer see this, event happen and doesn't care when you observed it.
For event, observer is irrelevant factor.

 

[Ibix]

But why this is speed of causality?

Nothing can travel faster so nothing can be affected earlier.

If there is a car accident, it's common for people to have other crashes because they're looking at the accident. The later crashes are caused by the first one. But if there is a car crash one light second away and you crash half a second later it cannot have been caused by the other accident because you can't have seen it at the time the accident happened. The invariance of the speed of light enforces that all frames will agree you couldn't have seen the crash yet at the time you crashed (or vice versa).

 

[Dale]

What has EM wave with causality?

EM waves can cause things.

If there is a finite invariant speed then anything massless travels at that invariant speed. If there is an invariant speed and causality then the invariant speed is the fastest speed at which any causal influence can travel. Light is the first massless thing that we understood, so it was the first thing we dealt with whose speed is the invariant speed. So we call the invariant speed the speed of light.

EM wave don't have nothing to do with causality.
Why would speed of causality be speed of light?

EM waves can cause things so of course they have something to do with causality.

The speed of causality is yet another term for the invariant speed. I don’t like that term because causality can also travel slower. But despite my opinion, it is a recognized term for the invariant speed

 

[user079622]

EM waves can cause things.

If there is a finite invariant speed then anything massless travels at that invariant speed. If there is an invariant speed and causality then the invariant speed is the fastest speed at which any causal influence can travel. Light is the first massless thing that we understood, so it was the first thing we dealt with whose speed is the invariant speed. So we call the invariant speed the speed of light.

EM waves can cause things so of course they have something to do with causality.

The speed of causality is yet another term for the invariant speed. I don’t like that term because causality can also travel slower. But despite my opinion, it is a recognized term for the invariant speed

Queen of UK become instantaneous queen of Australia.
The other thing is that people in Australia will have to wait a few milliseconds for information to reach them via TV.

 

[A.T.]

Queen of UK become instantaneous queen of Australia.

Instantaneous in which frame of reference?

The other thing is that people in Australia will have to wait a few milliseconds for information to reach them via TV.

Signal delay is removed in the usual simultaneity conventions.

 

[Ibix]

Queen of UK become instantaneous queen of Australia.

The late, great Sir Terry Pratchett hypothesised the existence of queons and kingons, particles that carry monarchy, and their antiparticle, the republicon. He notes that plans for an instantaneous communication device based on torturing a small king were interrupted by the bar closing.

Royalty is not a physical property that can be measured nor transmitted. It's a bunch of human made rules.

 

[WWGD]

I always thought that everything we learned in school of physics is 100% correct. Now I see that math and physics is very different in that aspect..
Can I say math is absolute truth, physics is just best current approximation for reality?

Depends on which Math you refer to, as it splits on every undecidable statement. Choice or no Choice, Archimedean axiom holds in Standard Model for Reals but not in other models such as the Hyperreals, etc.

 

[Dale]

Queen of UK become instantaneous queen of Australia.
The other thing is that people in Australia will have to wait a few milliseconds for information to reach them via TV.

And what physical measurement can her being queen of Australia cause in those milliseconds? Think about that carefully. What physical measurements can someone perform in Australia whose outcome depends on who is queen? What will be the outcome of those measurements be in those milliseconds?

She may instantaneously be queen of Australia, but that cannot cause any effect in Australia faster than light.

 

[fresh_42]

Queen of UK become instantaneous queen of Australia.
The other thing is that people in Australia will have to wait a few milliseconds for information to reach them via TV.

Reading a line in a book changes the information instantaneously, but the physical information that it changed is not instantaneous. We can only measure physical quantities. We do not have any information about what has or has not happened in that line before reading it. And this bit of information transfer takes time.

People in Australia actually never know whether they have a queen or a king in a given moment in time.

 

[Jaime Rudas]

Instantaneous in which frame of reference?

Westminster Abbey

 

[jbriggs444]

Westminster Abbey

Since the rest frame of Westminster Abbey is rotating, that leaves some remaining troubles with simultaneity.

 

[Jaime Rudas]

Since the rest frame of Westminster Abbey is rotating, that leaves some remaining troubles with simultaneity.

No, that's not true. Simultaneous events that occur in the same place remain simultaneous with respect to all reference frames, regardless of whether they are inertial or not or whether they rotate or not.

 

[jbriggs444]

No, that's not true. Simultaneous events that occur in the same place remain simultaneous with respect to all reference frames, regardless of whether they are inertial or not or whether they rotate or not.

We are not talking about events that occur in the same place. We are talking about an event occurring at Westminster Abbey (e.g. coronation) and a separate event occurring in Australia (the time there when the coronation is deemed to have taken place). Those two events are space-like separated.

We need a simultaneity convention for that. A rotating reference frame is a poor starting point for defining a simultaneity standard. A good choice would instead be an Earth-centered inertial frame.

 

[Dale]

A few recent posts about clearly non-physical things have been deleted. Thank you to those who wrote good information to correct some misconceptions.

Please remember, the topic of this thread is about axioms in physics. Relativity discussions belong in the relativity forum.

 

[WWGD]

I think a point that may be relevant here is that Mathematics isn't bound by Physical reality, as the Banach-Tarski Paradox whereby we can turn a ball B with volume V into two such balls with volume V each , through (relatively straighforward -- Mathematically) transformations, shows ; something that cannot be implemented physically.