Why can light "push" but not be "pushed?"

[swansont]

It is dropped.

I wonder if there is anyplace in this forum where I can challenge "length contraction" on macro-scale without continuing censorship. Just wondering.

 

You have 750 frikkin' posts. A large fraction of which were on this topic. That's some censorship.

 

The truth is that you beat it to death, and your only defense was basically a "that's not how it happens in the real world" application of philosophy. But this is a question of physics, not philosophy. As a question of physics, it is quite straightforward. If you apply the standards of science and the postulates of relativity, length contraction and time dilation are direct results. There is experimental confirmation of them. Conversely, rejecting these effects requires you to reject science.

 

The answer to your question is no, there is no longer any place in this forum where you can challenge length contraction. Numerous moderator notes should have made that clear. You can reread the lengthy threads already in place, because all of the answers are given in them, probably multiple times; this is part of the reason that no further discussion is possible.

[owl]

Owl is a long time relativity denier.

 

He has no real basis for this, other than he just can't accept it.

I will not allow such misrepresentation.

For the record, I am not a "relativity denier." I accept that GR is an improvement over Newtonian physics in calculating and predicting the movements of masses and light around other masses. The math and physics work well with the coordinates for space and time based on the GR model. I deny that mass curves something 'in the real world' called "spacetime."

 

I accept that the speed of light is constant as per SR. In fact I just learned more about its particulars by comparing different frames of reference in this thread and hearing the answers.

I deny that the length contraction part of SR makes planets change shape, earth's atmosphere get thinner, or the distance between planets and the sun or between stars get shorter, as it might *appear* from relativistic frames.

 

All of the above acceptance and denial is based on rational, reasonable thinking and what 'scientific realism' calls 'naive realism.'

If the claim that a flattened earth is just as valid as a nearly spherical earth is based on the length contraction part of relativity as 'scientific realism', then I remain a 'naive realist', insisting that earth keeps its nearly spherical shape no matter how it might appear from extreme frames of reference.

 

That is all. I am done now.

[Iggy]

In my experience the question usually goes something like this:

 

The muzzle velocity of a bullet fired from the front of a train plus the speed of the train gives the speed of the bullet compared to the train tracks.

 

However, the muzzle velocity of a laser fired from the front of the train plus the speed of the train doesn't give he speed of the laser compared to the tracks.

 

What gives? Why is light different?

 

DH pointed out the answer in post 11, and probably others as well, but being lost in so much obstinance maybe it could be repeated.

 

The first indented sentence is wrong. Simply adding one velocity to another doesn't give exactly the right answer. It gives very nearly the right answer at very slow speeds, but it gives increasingly bad results at increasing speeds.

 

The bullet and the laser both follow the correct velocity addition formula. It isn't that the bullet is Newtonian and the light acts different. What if the muzzle velocity of the bullet were 99% of the speed of light and it were shot from a ship going half the speed of light relative to earth? The combined velocity would hardly be 149% of the speed of light. As intuitive as it is, simple velocity addition doesn't work.

[swansont]

If the claim that a flattened earth is just as valid as a nearly spherical earth is based on the length contraction part of relativity as 'scientific realism', then I remain a 'naive realist', insisting that earth keeps its nearly spherical shape no matter how it might appear from extreme frames of reference.

 

For anyone following this other than owl, I will point out here that the emphasis is on naive. For one to insist on an intrinsic shape, one must adopt a preferred frame of reference in which that shape is measured, but from this postulate, many parts of physics simply fail to work the way we are used to, such as the laws of physics being the same in all frames of reference, or that measurement is not an illusion. One could investigate these new paths and see where they lead and then decide whether this is a viable approach to science. Or one can remain naive.

 

Put another way, relativity, like all of science, is not an a-la-carte menu. You don't get to pick and choose the parts you like and discard the rest.

[owl]

When I said at the end of my last post, "That is all. I am done now."

... that was a signal from the author of the thread that either it could be shut down now by a moderator... not unusual for my threads... or contributors could focus on specifics to which I am allowed to reply.

It clearly would not be fair to allow challenges to my last post, that I am not a "relativity denier," yet not allow my defense to each challenge, under my present gag rule restrictions.

 

Just one example; Swansont said:

For anyone following this other than owl, I will point out here that the emphasis is on naive. For one to insist on an intrinsic shape, one must adopt a preferred frame of reference in which that shape is measured...

 

"Intrinsic shape" means 'as it is' regardless of how it is observed or measured. As a "naive realist" I do not "... adopt a preferred frame of reference in which that shape is measured." ( I have a preference for being "at rest with" objects I observe and measure.)

 

I realize that naturally occurring shapes of objects like planets do not depend on relativity's "frames of reference" for their properties, including dimensions and distances between such objects, etc.

If the above reply violates (edit) 'my' gag rule, you can just ban me now and be done with it.

Edited June 23, 2012 by owl

[ACG52]

You don't get to pick and choose the parts you like and discard the rest.

 

He's been told that before, here and on other forums.

 

It does no good, he continues to misunderstand and deny relativity.

[owl]

 

Put another way, relativity, like all of science, is not an a-la-carte menu. You don't get to pick and choose the parts you like and discard the rest.

I take this to mean you believe that relativity is an all or nothing theory which is absolutely true in all respects and beyond all criticism.

Your additional phrase, "like all of science" is quite obscure in meaning. None of science can be criticized without all of it being rejected?

 

As to your second sentence, I don't need your permission to "pick and choose" the parts of relativity which I choose to criticize, as summarized above. And those parts do not invalidate my acceptance of GR's improved coordinate system for predicting the effects of gravity or SR's well established constancy of lightspeed.

[Iggy]

"Intrinsic shape" means 'as it is' regardless of how it is observed or measured.

It is sad to see a falsified world view turn into a religion. Earth has a secret shape that exists regardless of the shape we observe or measure earth to be. It is probably a triangle, but there is just no way of knowing.

 

One thing is sure... whatever the intrinsic shape is -- it is the same in every frame of reference, because that is the Newtonian expectation.

[ACG52]

I take this to mean you believe that relativity is an all or nothing theory which is absolutely true in all respects and beyond all criticism

 

The Theory of Relativity is not the words you use to describe it. It is the equations. You can't say 'this equation is valid and this one is not' because they all tie together.

 

If you are going to come up with a criticism of relativity, it has to be something more than 'I refuse to believe it' and 'that's not common sense'.

[owl]

Iggy:

...Blah, blah, blah...

As intuitive as it is, simple velocity addition doesn't work.

You're a little late in the game to come back to the bullet vs light illustration. And I'm the one who said that "there is no cumulative velocity for light."

 

Read the thread before you pop off.

 

My examples:

#4:

It's obvious with a bullet fired ahead from a moving gun, "pushing" it to its regular velocity plus the gun's velocity. But, of course that doesn't work for a light shone ahead of a high speed ship, as above.

#6:

My "bullet" example was intended to contrast cumulative velocity with the established fact that constant 'c' requires that there is no cumulative velocity for light shone ahead from a high speed ship.

#12:

I already said twice that my bullet example was an illustration of the difference between a mass gaining velocity as shot from a moving gun ("cumulative velocity") and the fact that light does not gain velocity in a similar manner.

[Iggy]

Iggy:

...Blah, blah, blah...

as intuitive as it is, simple velocity addition doesn't work

 

You're a little late in the game to come back to the bullet vs light illustration. And I'm the one who said that "there is no cumulative velocity for light."

 

Read the thread before you pop off.

 

My examples:

It's obvious with a bullet fired ahead from a moving gun, "pushing" it to its regular velocity plus the gun's velocity. But, of course that doesn't work for a light shone ahead of a high speed ship, as above.

DH was trying to tell you earlier and I'm trying to tell you now that you are mistaken.

 

Adding the muzzle velocity of the bullet to the velocity of the train doesn't give you the exact velocity of the bullet relative to the ground. That simple velocity addition (w=u+v) that you call "obvious" in your quote is called Galilean velocity addition, it is part of Newtonian mechanics, it is intuitive, and it is wrong.

 

To get the exact answer for the bullet and for the laser you have to use the correct velocity addition formula:

 

[math]w=\frac{u+v}{1+uv/c^2}[/math]

 

It is a little more complicated than simply adding u and v, but it gives the right answer in both situations. Your assumption that the velocity of light adds differently than the velocity of the bullet is mistaken.

 

EDIT:

 

physics faq for velocity addition: http://math.ucr.edu/home/baez/physics/Relativity/SR/velocity.html

Edited June 23, 2012 by Iggy

[swansont]

I take this to mean you believe that relativity is an all or nothing theory which is absolutely true in all respects and beyond all criticism.

Your additional phrase, "like all of science" is quite obscure in meaning. None of science can be criticized without all of it being rejected?

 

As to your second sentence, I don't need your permission to "pick and choose" the parts of relativity which I choose to criticize, as summarized above. And those parts do not invalidate my acceptance of GR's improved coordinate system for predicting the effects of gravity or SR's well established constancy of lightspeed.

 

I look back and I don't see where I said you can't criticize. I said reject. I don't believe they are the same thing.

 

The problem with a myopic rejection of parts of science, based on philosophy rather than empirical testing, is that many parts of science are interconnected. You reject one part and it has implications, some of which I've spelled out here. It's quite similar to creationism, where ideology causes rejection of some science, but ends up having an impact on pretty much all of science, because the basic principles that are rejected apply more broadly. That's the problem with forming a world view without checking with mother nature to see if she agrees with it. In science, that's an absolute requirement.

[hypervalent_iodine]

... you can just ban me now and be done with it.

 

Done and done.