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Why is special relativity still being taught?


jduff
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Just a observation. While I can see special relativity being known as a archaic incorrect form. Maybe historical reference? Something that might be useful to learn before general relativity? I do not see any benefit from it being taught in this day and age. Are there really scientists who still believe gravity is a force? ?!?

Edited by jduff
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I don't think special relativity is either archaic or incorrect. It is accurate for conditions where there is no (or little / constant) gravity. It is mathematically simple and easy to understand. General relativity requires advanced mathematics so it makes sense to teach SR to undergrads.

 

 

Are there really scientists who still believe gravity is a force?

 

I'm not sure how that is relevant as SR specifically excludes gravity (as a force or otherwise). However, Newtonian gravity is still used because (again) it is much simpler than GR and good enough in most cases.

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While I can see special relativity being known as a archaic incorrect form.

 

This is a gross misstatement of current understanding.

 

Special relativity holds well whenever we have very weak gravitational fields and so covers a wide range of phenomena. Importantly the standard model of particle physics has special relativity at its heart and this agrees with nature to a huge degree of accuracy.

 

 

Something that might be useful to learn before general relativity?

This is true, but under represents the importance of special relativity in understanding our Universe.

 

I do not see any benefit from it being taught in this day and age.

There are lots of reasons why special relativity is taught today. It agrees well with nature for a wide range of phenomena, but more than this it gives a not too difficult set-up in which some of the principals of what physics should be can be stated. In particular the whole notion of physics not really depending on how you chose to describe it.

 

If one goes on to study general relativity and or quantum field theory (including stings here) then a good understanding of special relativity is required. But not all physics students study these subjects and so the reasons above justify the inclusion of special relativity in an undergraduate course.

 

Are there really scientists who still believe gravity is a force? ?!?

Depends on what you mean exactly by a force. A test particle is accelerated while in a gravitational field and so we have a force. But if you look at the action of a test particle you see there is no external force term, and so gravity appears not as a force but a pseudo-force.

 

The difference is technical and so I consider gravity a force, just taking care with what I have said above.

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If one goes on to study general relativity and or quantum field theory (including stings here) then a good understanding of special relativity is required. But not all physics students study these subjects and so the reasons above justify the inclusion of special relativity in an undergraduate course.

 

 

Depends on what you mean exactly by a force. A test particle is accelerated while in a gravitational field and so we have a force. But if you look at the action of a test particle you see there is no external force term, and so gravity appears not as a force but a pseudo-force.

 

The difference is technical and so I consider gravity a force, just taking care with what I have said above.

So, exactly what do you mean by accelerated? If, lets say our current sun were to explode. Would the earth lose its gravitational field before we on(the observer) earth realized the sun had exploded?

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So, exactly what do you mean by accelerated? If, lets say our current sun were to explode. Would the earth lose its gravitational field before we on(the observer) earth realized the sun had exploded?

 

The earth's field would be unaffected. The sun's field at our location would remain intact as long as the mass remained spherically symmetric inside of our orbit. Thus, we would realize the sun exploded before our orbit was affected. That's all classical physics. No relativity involved.

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Without any details, I mean that the velocity of the particle is not constant.

So would this acceleration apply to a SOL particle, like a neutrino ect?

 

The earth's field would be unaffected. The sun's field at our location would remain intact as long as the mass remained spherically symmetric inside of our orbit. Thus, we would realize the sun exploded before our orbit was affected. That's all classical physics. No relativity involved.

The question was directed to Ajb, not you Swanson. If the question or statement was to be directed at you, I would quote you! Also if it was a general question it would not have a quote!

Edited by jduff
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jduff, on 29 Dec 2013 - 7:41 PM, said:

The question was directed to Ajb, not you Swanson. If the question or statement was to be directed at you, I would quote you! Also if it was a general question it would not have a quote!

That was very bad manners towards Swansont. He is more than able to answer your question. Since when was it a crime to respond to a post where somebody else was quoted?

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The question was directed to Ajb, not you Swanson. If the question or statement was to be directed at you, I would quote you! Also if it was a general question it would not have a quote!

Perhaps you aren't clear on how discussion boards function.

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That was very bad manners towards Swansont. He is more than able to answer your question. Since when was it a crime to respond to a post where somebody else was quoted?

You are perhaps right. Everyone that frequents this forum often knows Swansont is quite capable of answering most questions. The base of the argument was with ajb. So the question was directed on his statement. Which ajb still can answer!

 

Also, I do not view a poster here as greater or lesser than another poster. Regardless of a community's stature.Keep that in mind! Chastising, now that is amusing! This may perhaps help! http://forum-services-review.toptenreviews.com/25-forum-posting-etiquette-tips.html

 

Now if we can get back on topic!

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!

Moderator Note

 

jduff - fyg anyone can answer questions and enter the debate - this is a discussion board not a private chat room.

 

Try to avoid telling other members what they can or cannot say. Btw - We also have our own etiquette rules drawn up by one of our exalted admins.

 

(nb neutrinos do not travel at the SofL they are just a tiny but important bit slower as they have mass)

 

Please do not respond to this note within the thread.

 

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So would this acceleration apply to a SOL particle, like a neutrino ect?

Neutrinos have a very small mass and so never travel at the speed of light. But anyway, the acceleration will apply to photons for example. But we have to be a little careful here as we do not have a proper time for photons and so cannot parametrise their paths in the same way we can for massive particles. They do not follow straight lines, but rather the follow the next best thing- null geodesics.

Which ajb still can answer!

Swansont answered the question perfectly. I have nothing to add.

Edited by ajb
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Neutrinos have a very small mass and so never travel at the speed of light. But anyway, the acceleration will apply to photons for example. But we have to be a little careful here as we do not have a proper time for photons and so cannot parametrise their paths in the same way we can for massive particles. They do not follow straight lines, but rather the follow the next best thing- null geodesics.

 

Swansont answered the question perfectly. I have nothing to add.

Actually ajb, neutrinos have zero mass, they only retain mass after encountering it. There are a infinite amount of neutrinos in the universe that are SOL particles. The only reason those here and you apply neutrinos as having mass is due to this particular facet. Observable neutrinos have mass due to having encountered mass along its path. Which only is obvious. But everyone here fails to mention!

 

As to Swansont's response, he is partially correct. Except, that was not what I am looking at. Relativity does play a role and here is how. Space, Time, Mass.. Light in-particular. According to special relativity and using gravity as a force. Gravity would be faster than light. Which directly contradicts certain laws. Why the general theory of relativity was made by Einstein. As it corrects special relativity. As well as shows gravity is not a force.

Edited by jduff
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Neutrinos can't oscillate if they are massless.

 

According to GR, gravity signals propagate at c. SR does not address gravity, so any claim about gravity "according to SR" is misplaced. Regardless, however, if the mass of the sun remained spherically symmetric and within the orbital radius of the earth, we would feel no change in it, regardless of its propagation speed.

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Actually ajb, neutrinos have zero mass, they only retain mass after encountering it. There are a infinite amount of neutrinos in the universe that are SOL particles. The only reason those here and you apply neutrinos as having mass is due to this particular facet. Observable neutrinos have mass due to having encountered mass along its path. Which only is obvious. But everyone here fails to mention!

Can you give some reference here?

 

It is true that neutrino mass is an awkward thing in light of the standard model, but as Swansont states, without some mass we cannot have neutrino oscillation. Unless you are aware of some other models?

 

According to special relativity and using gravity as a force. Gravity would be faster than light. Which directly contradicts certain laws. Why the general theory of relativity was made by Einstein. As it corrects special relativity.

Okay, it is true that Newtonian gravity is a long range force and has instantaneous interactions. It is also true that GR tells us that small changes in the gravitational field propagate at the speed of light.

 

 

As well as shows gravity is not a force.

Right, within GR you can interpret gravity as a pseudo-force, which is directly related to there being no true inertial frames of reference.

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So, exactly what do you mean by accelerated? If, lets say our current sun were to explode. Would the earth lose its gravitational field before we on(the observer) earth realized the sun had exploded?

The Earth gravitational field is created by the Earth, so what happens to the Sun is irrelevant, your question makes no sense.

Moreover, if the Sun "exploded", the gravitational field of the resulting bits and pieces would still be there, so the gravitational field of the "exploded Sun" would be present.

If the Sun magically "disappeared", then , it would take about 8.3 minutes for the effect to be felt on Earth, since the gravitational waves propagate at the speed of light and it takes light about 8.3 minutes to propagate from the Sun to the Earth.

Edited by xyzt
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If the Sun magically "disappeared", then , it would take about 8.5 minutes for the effect to be felt on Earth, since the gravitational waves propagate at the speed of light and it takes light about 8.5 minutes to propagate from the Sun to the Earth.

 

There is no evidence that gravitational waves do exist. They have not been detected by devices.

Edited by Sensei
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There is no evidence that gravitational waves do exist. They have not been detected by devices.

This is because the sources (binary stars) are very weak. If the Sun "disappeared", the effects would be detectable : the Earth would continue on a tangent to the current elliptical trajectory, never to return to the same point, the passage of seasons would disappear.

Just a observation. While I can see special relativity being known as a archaic incorrect form. Maybe historical reference? Something that might be useful to learn before general relativity? I do not see any benefit from it being taught in this day and age. Are there really scientists who still believe gravity is a force? ?!?

SR is instrumental in the design of particle accelerators.

SR is instrumental in determining the amount of energy released in a nuclear reaction.

SR is instrumental in ....

Edited by xyzt
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Just a observation. While I can see special relativity being known as a archaic incorrect form. Maybe historical reference? Something that might be useful to learn before general relativity? I do not see any benefit from it being taught in this day and age. Are there really scientists who still believe gravity is a force? ?!?

 

Einstein did not think of gravity as a force, he thought of it as a distortion of space time due to the presence of mass.

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  • 3 weeks later...
a different observation

I can see that relatively close is almost yet not quite the same as same as. Thus I am wont to wonder why others simply will not. What's up with that? Really; how is it some still believe curvature is force and gravity is not? Be nice now.


ron

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What would the time dilation effect be in two hypothetical objects accelerating towards each other, at 99.999% c?

 

SR allows for an object to get as close as 99.99 % c thus , both object could be traveling through space at said speed?

Edited by Alan McDougall
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What would the time dilation effect be in two hypothetical objects accelerating towards each other, at 99.999% c?

 

You need to use the velocity addition formula: http://en.wikipedia.org/wiki/Velocity-addition_formula#Special_theory_of_relativity

 

Their relative speed would be about 99.999999995% the speed of light. I'll leave it to you to plug that into the Lorentz equation... (it is about 10,000, I think).

Edited by Strange
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