Is acceleration absolute and velocity not?

[prasanth.s]

Am new here
Lets limit our discussion to Classical Mechanics.

Any of the 'accelero-detectors' mentioned in a post above(simple pendulum, etc.) will work inside a spherical shell whirled around in a circle using a string(or inside a bus taking a turn). But will they work inside a satellite going around the earth?
Ans: No
Reason: Because it is in free fall
Natural follow-up question: So what? Why is that the reason?

This raises questions about which forces can be felt or detected(alternatively which accelerations are detectable)

My claim is that if you have a force acting on every point(mass) on a body producing same acceleration on each(like gravitational force except that g is constant throughout the body) then there is no way for the body to detect the force. It can only figure out if it is accelerating or not by observing its surroundings for RELATIVE accelerations.

And if there is type of force (theoretically-there may not be such a force falling into the list of four basic forces in nature) that can never be detected it means that ACCELERATION IS RELATIVE

 

[Mueiz]

is acceleration absolute..is it, cause velocity isn't.

In gravitational field it is absolute and equal zero in free-falling frames.
In the absence of gravitational field it is relative.

 

[Dale]

In gravitational field it is absolute and equal zero in free-falling frames.
In the absence of gravitational field it is relative.

But according to you there is always a gravitational field and therefore it is always absolute. Stop posting nonsense that even you don't believe has any physical meaning.

 

[Dale]

Am new here ... ACCELERATION IS RELATIVE

Hi prasanth.s, welcome to PF. Usually rather than responding to a post which is 6 years old it is better to start a new thread. That said, there are two kinds of acceleration that we can discuss, one is called "proper acceleration" and it is absolute, the other is called "coordinate acceleration" and it is relative. If you would like to discuss the difference I recommend a new thread.

 

[K^2]

what about rotation?

can an observer decide whether his or her frame of reference is rotating or not? can different observers agree?

You can set up a gravitational field that will make any local experiment confirm rotation without there actually being any rotation. Frame dragging can even simulate Coriolis Effect.

 

[Mueiz]

But according to you there is always a gravitational field and therefore it is always absolute. Stop posting nonsense that even you don't believe has any physical meaning.

If gravitational field has a physical meaning then the absence of gravitational field must also have a physical meaning..whether it exists or not this is another topic (ideal gas does not exist but has a physical meaning ).
It is a bad way in discussion to tell someone to stop posting.
This is an independant thread and I hope we will forget our previous discussions

 

[Dale]

If gravitational field has a physical meaning then the absence of gravitational field must also have a physical meaning.

No. If it is impossible, even in principle, to experimentally test your assertions about the absence of a gravitational field then the concept has no physical meaning. It is pure speculation with no basis in science.

It is a bad way in discussion to tell someone to stop posting.
This is an independant thread and I hope we will forget our previous discussions

I would be more than glad to forget our previous discussions if you would stop posting the same absurd claims again.

 

[Mueiz]

No. If it is impossible, even in principle, to experimentally test your assertions about the absence of a gravitational field then the concept has no physical meaning. It is pure speculation with no basis in science.

Tell me what is the experiments done to assert that the entropy of a system of zero temperature (which is impossible practically as stated by the third law of thermodynamics) is absolute and independant of other properties...not all scientific facts need to be experimentally tested to gain physical meaning.

 

[Mueiz]

I would be more than glad to forget our previous discussions if you would stop posting the same absurd claims again.

If you use logical arguments rather than prejudice and unreasonable rejection to covince me I will stop easly.

 

[Mueiz]

A rotating object is also accelerating absolutly, just spin real fast in a circle and see what your arms tend to do.

After reading this I made a quick Journey to a place which is very far from any star and spun real fast in the absence of gravitational field and saw that my arms was not affected
by this spinning .. in fact I was not sure whether I was spinning or not because there is no effect for spinning in the absence of gravitation nor there is a system to measure acceleration relative to it.

 

[Dale]

I made a quick Journey to a place which is very far from any star and spun real fast in the absence of gravitational field

That is very impressive, particularly since according to you there is no place in the universe which is far enough away when I asked you how far you had to go. And in fact you even asserted that your own gravitational field would be sufficient to violate this.

 

[Mueiz]

That is very impressive, particularly since according to you there is no place in the universe which is far enough away when I asked you how far you had to go. And in fact you even asserted that your own gravitational field would be sufficient to violate this.

This is a thought experiment and it is not neccesary to be possible practically
When you ask me how far I had to go you surely think of practical experiment so the answer must be nowhere ... if this is the way we deal with thought experiments then all thought experiments are incorrect because all of them contain idealization and practical impossibility

 

[Deric Boyle]

would like everyone's attention.The word 'invarint' is again ambigous like absolute. And may I ask why every body is bringing mathematical formalism to it. The birth of 'accelaration' took when human perceived object speeding past them so the real definition is 'how fast is something moving' but how do we define fast? We take something slow or say by observing it so. So you can see what I am writing that is the observer is INSEPARABLE.So, acceleration is never absolute but it relative.If not, then point me out something in universe which is at rest or from which everything, everything is moving away.
Thank you

 

[Deric Boyle]

Mueiz your GEDANKEN KUCHE is like anything.
Anways a problem for all, after getting inspired from Mueiz,
you are in a space where gravitation doesn't hold. Now there is a metre rod which your facing but far from your reach.You could only see it.
Now you both are roating for me but you don't know that you both are.All you see is the metre rod lying dead before you.Now nothing is given to you accept you yourself.
Now tell how can you find out that you are roating and in what direction with respect to metre rod?

 

[Dale]

This is a thought experiment and it is not neccesary to be possible practically

No, but it is necessary to be possible in principle, which yours is not.

When you ask me how far I had to go you surely think of practical experiment so the answer must be nowhere ... if this is the way we deal with thought experiments then all thought experiments are incorrect because all of them contain idealization and practical impossibility

Again, this is not an issue of practicality. You have declared that even the gravitational field of an accelerometer is sufficient to prevent the effect that you continue to assert. So the experiment is impossible even in principle since you cannot even in principle have a massless accelerometer.

Regarding the other idealizations that you have mentioned: ideal gasses and absolute zero. These are both unacheivable ideal states which we can approximate arbitrarily closely, and as we get arbitrarily close to the ideal state we get results which are arbitrarily close to the predictions of the ideal state. The ideal state is simply a limiting case.

Your situation is quite different. You are proposing that upon reaching your ideal state a radically new behavior will suddenly emerge, a behavior which is not even approximated if you are arbitrarily close to the ideal state. This is what makes your idea unscientific speculation. By design, it is unfalsifiable and makes no testable predictions, and does not even approximate the behavior of any experiment.

 

[Mueiz]

No, but it is necessary to be possible in principle, which yours is not.

Again, this is not an issue of practicality. You have declared that even the gravitational field of an accelerometer is sufficient to prevent the effect that you continue to assert. So the experiment is impossible even in principle since you cannot even in principle have a massless accelerometer.

Regarding the other idealizations that you have mentioned: ideal gasses and absolute zero. These are both unacheivable ideal states which we can approximate arbitrarily closely, and as we get arbitrarily close to the ideal state we get results which are arbitrarily close to the predictions of the ideal state. The ideal state is simply a limiting case.

The two cases is the same because in the case of absolute zero the thermometer must cause the temperature of the system to increase because there is no thermometer with absolute zero temperature just like the case of massless accelerometer.
The law of independance of entropy in absolute zero is also radical because entropy dependence on other properties of the system does not tend to zero when the temperature goes to absolute zero.(I am ready to open new thread in classical thermodynamics to prove this if you do not agree with me )

 

[Dale]

The two cases is the same because in the case of absolute zero the thermometer must cause the temperature of the system to increase because there is no thermometer with absolute zero temperature just like the case of massless accelerometer.

So what? You can make a thermometer with arbitrarily close to absolute zero temperature and you can get experimental results arbitrarily close to the results you would predict at absolute zero. In your case you can go arbitrarily far away from any significant source of gravitation and use arbitrarily small accelerometers and still not get experimental results even remotely close to the results you are predicting.

 

[Mueiz]

So what? You can make a thermometer with arbitrarily close to absolute zero temperature and you can get experimental results arbitrarily close to the results you would predict at absolute zero. In your case you can go arbitrarily far away from any significant source of gravitation and use arbitrarily small accelerometers and still not get experimental results even remotely close to the results you are predicting.

I said in my last post that the law of independace of entropy in absolute zero is also radical ... approximation is not the only way to know the laws of ideal cases there are the philosophical principles of science (simplicity,similarity,sufficiant reason etc.) and there are thought experiments and indirect experiments .. there is guessing !
In gravitational fied there is the special frame of the free-falling which gives the meaning of absolute acceleration ..while in zero gravitational field there is no free-falling.

 

[Dale]

In gravitational fied there is the special frame of the free-falling which gives the meaning of absolute acceleration ..while in zero gravitational field there is no free-falling.

Show me one piece of experimental evidence supporting this assertion even approximately.

 

[Mueiz]

Show me one piece of experimental evidence supporting this assertion even approximately.

I will show you ...please wait me until i find a good massless accelorometer

 

[Dale]

Once you find some experimental evidence even approximately supporting your claim feel free to come back and discuss. Until then, stop posting your unsupported personal theories. It is against the rules of PF.

 

[Mueiz]

Once you find some experimental evidence even approximately supporting your claim feel free to come back and discuss. Until then, stop posting your unsupported personal theories. It is against the rules of PF.

When you find that the rules of science do not sopport your unreasonable claims you seek help in the rules of PF which will not help you too.
What is your reply to my example of the law of entropy and to may statements that direct experiment is not the only method of science?!

 

[Dale]

When you find that the rules of science do not sopport your unreasonable claims you seek help in the rules of PF

The rules of science do not support your unreasonable claims either.

What you have is a Machian philosophical stance that you desparately wish to believe regardless of any evidence. You look around at the evidence and see that it does not support your preconcieved philosophy, so you invent a radically different behavior at an impossible idealized limit in order to rescue your philosophy and make it unfalsifiable.

What is your reply to my example of the law of entropy and to may statements that direct experiment is not the only method of science?!

Your attempt to sidetrack the discussion with thermodynamics is very off-topic and transparent. If you wish to have a discussion about thermodynamics you should start a new thread.

 

[Mueiz]

The two cases is the same ... entropy dependence on other properties of the system does not tend to zero when the temperature goes to absolute zero.(I am ready to open new thread in classical thermodynamics to prove this if you do not agree with me )

Meet me in a new thread' "Is the law of entropy radical or smooth ? " and after that let us come back again to the absolute acceleration .

 

[Dale]

The acceleration question is not related to thermodynamics and your introduction of the topic is merely a diversion.

 

[Mueiz]

The acceleration question is not related to thermodynamics and your introduction of the topic is merely a diversion.

I used the example of thermodynamics to confirm my statement ''that direct experiments are not the only method in physics '' which i used to defend using pure theoritical method to show that acceleration is relative in the absence of gravitational field'' but you posted your objection that i have to get an experimental prove.

 

[Dale]

Experiments are what distinguish science from philosophy or math.

 

[K^2]

Well, to be fair, experiments are fairly useless here. GR is tested to 12 decimal places. So we know that assumption of absolute acceleration is at least that good. But if we compare it to Mach's Principle, we need to see a significant enough fraction of the universe accelerate in order to actually see a difference greater than 10^-12. Galaxy collisions are a few orders of magnitude off. We're not going to get an experiment that distinguishes the two.

But GR works, unlike pretty much everything that has been suggested in its place. So for now, as far as physics goes, acceleration is absolute. Everything else is for philosophers and theologists to discuss.

 

[Mueiz]

Experiments are what distinguish science from philosophy or math.

If you said that my opinion was philosophy or math in the beginning of the discussion ,i might would have agreed with you , but instead you used very unkind words against my post
Ok anyhow if philosphy and math are not science this is only a terminological point .but what is clear and important is that pure theoretical thoughts have its great role in science generally .One of hundereds of examples is the (impossible) thought of Einstein of chasing the light wave which led him to SR

 

[Dale]

what is clear and important is that pure theoretical thoughts have its great role in science generally

Not unless they eventually lead to testable predictions.