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Physics, Astronomy & Cosmology / Re: Does a particle's weight increase with speed? More on relativistic mass.

« on: 23/07/2016 11:29:49 »

I came across a special relativity text which says A particle does not become heavier with increasing speed. Do you believe the author is correct?

I think it's wrong, on the particle there should be a greater force, proportional to the gamma factor. But maybe the author intended to refer to its mass and not to its weight (which kind of book is it? Is it a universitary text?)

What would you expect would happen to the magnitude of the gravitational field if the source of the field was moving?

Don't know, but is it really the same question as the particle's weight?

Authors who don't use and don't like the concept of relativistic mass make arguments such as the following which are from Appendix F in the text Special Relativity by T.M. Helliwell page 259. I'm going to paraphrase a bit to save myself some typing but the essence of what I'm quoting will not be changed. The author uses the symbol m_R to represent relativistic mass.

(i) By hiding √{1 - v²} in the mass, we may forget it is there. ...

(ii) One may get the mistaken impression that to go from classical to relativistic mechanics its only necessary to replay all masses by m_R. This certainly works for the momentum p = m_Rv, but it does not work, for example, for kinetic energy: The relativistic kinetic energy is not (1/2)m_Rv². And it works in Newton's second law F = ma only in the very special case where the force exerted on a particle is perpendicular to its velocity. In all other cases F != ma.

(iii) Relativity fundamentally serves to correct our notions about time and space. That is, it is really the dynamical equations dealing with motion, like energy and momentum, that ought to be changed, and not the properties of individual particles, like mass.

(iii) When relativity is cast in four-dimensional spacetime form, ...., the idea of relativistic mass is out of place and clumsy.

I agree with these three points and I would even add others, but I've already discussed about them in many other threads. All of this in SR only, however, even because I don't know anything of GR.

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Physics, Astronomy & Cosmology / Re: Can electricity travel faster than light?

« on: 21/07/2016 18:27:34 »

I know that if we switch on a torch on a train, the speed of light cannot be added to that of the train. What about speed of electricity on a wire? Can it be added to the train's speed?

It depends on
1) what you intend with "speed" (speed of what?)
2) what you intend with "electricity"

Just to make an example, the phase velocity of electromagnetic waves in a wave-guide can be greater than c. Even the group velocity of an electromagnetic wave, in a suitable medium, can be faster than c.
What instead must always be less then or equal c is signal velocity
http://www.mathpages.com/home/kmath210/kmath210.htm

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Physics, Astronomy & Cosmology / Re: Do Photons exist?

« on: 15/07/2016 13:22:36 »

There is a lot of science that is based around the Photon, does the Photon exist?

Here is described how to prove in laboratory that photons really exists, that is, it's described a definitive proof of their existence:

http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf

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Physics, Astronomy & Cosmology / Re: What determines the spectrum produced by hydrogen?

« on: 31/05/2016 12:45:53 »

Usually molecular transitions have much lower energy than atomic transitions, so if you excite with an electric discharge the ordinary molecular hydrogen, you will find line emissions of the atomic spectrum, together with line emissions of the molecular, but these last are almost in the infrared so if you look at the visible + UV part of the spectrum, you will find only atomic lines.

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Physics, Astronomy & Cosmology / Re: Will an object ''contract'' to a singularity at the ''speed'' of light?

« on: 31/05/2016 12:39:09 »

If an object could travel away from a light source at the near ''speed'' of light or the ''speed'' of light, the object would not gain any energy from the ''trailing light'' and without ''entropy'' gain the object would only have ''entropy'' loss and contract to a denser ''mass'' and become a ''cold'' object?

Sincerely I haven't understood all of what you are saying.
Anyway, *in this exact moment* I am travelling very near to light speed c, with respect to some very fast elementary particle, but I'm not a singularity at all...
If you don't have understood my answer you can ask.

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New Theories / Re: What is the speed of light really?

« on: 17/05/2016 07:42:30 »

There seems to be a lot of confusion about the speed of light. For instance some die hard Quantum Mechanics adherents, still believe that the speed of light follows Galilean transformations:

Depending on what you mean you could be wrong. If you mean that if, in the inertial frame S, a beam of light was moving from along the x-axis in the positive direction with speed c and another beam was moving along the same x-axis in the negative direction with speed c then their relative speed of the two beams is 2c. What SR states is that that will be the same in any inertial frame of reference.

This statement indicates such an extremely poor understanding of  special and general relativity, that it is quite depressing to realize that the most eager supporters of Quantum Mechanics, the ones who are willing to stand up for it no matter what, are the ones who do not realize that Quantum Mechanics does not claim to yield answers that satisfy ‘reality’.  This is true regardless of whether one is thinking in terms of multiple dimensions, or of the invariance of the speed of light in a vacuum. Supporters of the type I refer to will insist that it is not dimensions that are in question but “degrees of freeedom’. In the same  way these supporters will also argue about the speed of light being constant, in the terms quoted above, Apart from this they are extremely abusing and lofty in their self regard and disparaging of those who try to state the facts as they exist. He following are examples:

Quote from: McQueen
 This means that if they were 300,000 km apart, they would meet after 0.5 seconds and not  after 0.25 seconds as would have been the case had Galilean transformations  held good. This was extremely puzzling,

PmbPhyThat's because you have a misunderstanding of the invariance of c postulates of relativity.

Having pointed out this seeming unwillingness on the part of certain QM supporters to accept the fact that the very definition of Quantum Mechanics is that nothing can be defined in the classical sense of the term, it is time to return to the question of what does the term speed of light as constant mean ?

I had demonstrated  earlier by mathematical examples , how the speed of sound is invariant in a given medium provided the medium does not undergo a change:
For instance take the example of two cars; car (a) at 60 kmh and car (b) at 30 kmh  approaching each other from opposite directions at a distance of 10 Km. Their combined speed would be 60kmh + 30 kmh = 90 kmh. This can easily be verified by calculating at what point the two cars would meet if they maintain the same constant speeds. Since the distance between them is 10 Km, it will take 10/90 = 0.111 hours for the two cars(a) and (b) to meet. During this time Car (s) would have travelled 3.33 Km and  car (a) would have traveled = 6.6666 Km  Thus the time taken for  the two cars meet is the time calculated according to their combined velocities 60 kmh and 30 kmh = 90 kmh.  The same kind of relationship holds true in general for any two bodies moving with respect to each other.  If two people (a) and (b) are walking towards each other from an initial starting distance of 1 km and their speeds respectively are 5 kmh and 3 kmh, then their speed with respect  to each other is 8 kmh and to verify this it is found that if they continue to maintain these same speeds that they will meet after 7.5 minutes, during this time (a) would have travelled 0.625 Km, and (b) would have travelled  0.375 Km. making a total of 1 Km.

 Yet coming back to the first example take car (a) travelling at 60 kmh is 1 km distant from car (b) travelling at 30kmh. Suppose that at this time car(a) activates a siren and also suppose that the speed of sound is  340m/s . At what time will the sound reach car(b) supposing that car(a) and car(b) continue to approach each other at the same speeds.  Would Galilean transformations apply and the combined speed with which car(a) and car(b) together with siren sound be 16.6m/s + 340m/s + 8.3m/s = 365m/s approx and they would meet at 1000/365 = 2.75 seconds. The answer is NO. Because the speed of sound is invariant in a medium it means that it does not obey Galilean transformations, thus the time taken for the sound of the siren to reach car (b) would be 1000/340 = 2.95 secs. During this time car (b) would have travelled 24.5 m approx.  This is a completely unexpected result, until one realizes that light also exhibits such invariance:

That is, if two beams of light were approaching each other  they would not follow Galilean transformations and have a combined speed of 600,000 km per second but each beam of light would have a constant speed of 300,000 km per second. This means that if they were 300,000 km apart, they would meet after 0.5 seconds and not  after 0.25 seconds as would have been the case had Galilean transformations  held good.

 The natural conclusion that one comes to on witnessing this circumstance, is, that the invariance that light demonstrates as it travels through a vacuum could very well be because it is travelling through a medium whose presence has thus far managed to elude us. The point being that this ( to some) is a more acceptable explanation than to believe in time dilation or the fact that objects shrink as they approach close to the speeds of light. The irony being that these physical properties may very well manifest themselves, even if a medium (aether) for light to travel through does exist. But they would manifest themselves not because the speed of light is a constant but because an aether exists.

Which movie have you seen recently?

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Physics, Astronomy & Cosmology / Re: Why does an interference pattern occur when electrons are fired one at time in t

« on: 28/04/2016 12:53:49 »

I know that is what most, if not all, physicists hold to be the case. However I myself would never speak of it in such terms. The reason for my position is that such a self-interference of a single particle with itself cannot be observed. It's not even clear to me what it means in practice. I know that it sounds nice and comfortable to speak of it that way but I have my reasons to disagree, and I hold that these reasons are strong. Here's my reasoning. Take a single particle and fire it at a double slit screen such as the one in Young's double slit experiment. The particle will strike the screen at one single location. In that experiment there is no evidence of a particle interfering with itself. If we have a large ensemble of identical setups there will be a pattern which emerges when we compare the results from all experiments. That does not imply that the particle interferes with itself.

I agree.

So why is there a pattern? What determines the geometry of the pattern? There's a pattern because the double slit is in reality a potential well. The shape of the potential well determines what the wave function will be.

You mean the potential is infinite on all the first screen's points excepting on the slits' points where it is zero?

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Physics, Astronomy & Cosmology / Re: Can gravity really interact with itself?

« on: 19/03/2016 11:37:15 »

According to GR, there isn't any gravitational field.

I am no expert (and I can't read German), but I heard that Einstein originally produced General Relativity as a gravitational field theory, inspired by Maxwell's electromagnetic field theory.

The geometric interpretation and application of Riemann Geometry came soon after, when people realized that Einstein's equations were similar to those developed for quite different purposes - which opened up a new set of mathematical tools which could be applied to General Relativity.

Perhaps the analytical advantages of the geometric interpretation have overshadowed the original field theory?

I only know that Einstein tried a lot but at the end, only the geometrization of spacetime worked, all the other methods didn't.

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Physics, Astronomy & Cosmology / Re: Can gravity really interact with itself?

« on: 19/03/2016 11:22:36 »

Not so fast lightarrow...
GR is a theory of gravity.  We do in fact observe there to be gravitational fields,

No. Where would you observe such "gravitational fields" if you use GR?

and, to say so, how do you then explain the GR 'field equations'.  What 'field' are they equating?

It's just a name. IIRC, Einstein initially  called them "equations of the gravitational field" but then he realized it was wrong and so changed the name in "field equations of gravity" or something alike.

The Maxwell equations are a description of the electromagnetic fields and cannot be linked to gravity via GR.

And what does it relate with what I wrote about GR?

What are you saying here?  Are you stating that GR constitutes an incorrect description of gravity? 

?
It's writing "gravitational field" which is wrong in GR because is to interprete GR in an incorrect way.

That by stating a phenomenon that we know exists as non existent, that GR just 'fixes' the fact of the existence of a gravitational field by simply ignoring it?

You're wrong. The existence of a "gravitational field" is not a "fact", is just "a theory-dependent interpretation".
According to newtonian theory, gravity is a field, according to GR is not.

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Physics, Astronomy & Cosmology / Re: Can gravity really interact with itself?

« on: 14/03/2016 17:17:43 »

I have seen it stated that since the gravitational field has energy it can produce gravity just like mass does. Is this necessarily true?

According to GR, there isn't any gravitational field.
Fixed.  []


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Physics, Astronomy & Cosmology / Re: Why are superconductors both attracted and repelled by a magnet?

« on: 12/03/2016 12:47:03 »

I saw a terrific demonstration the other day by a superconductor physicist whom we were recording for the programme next week; she had a circle of powerful magnets arranged around the outer edge of a large disc resembling a coffee table top.

Above this ring of magnets she placed a small puck (2 inch by 2 inch) of a copper oxide based superconductor cooled to -200C. The puck hovered about 2cm above the table top and, when given a push, followed the path of the magnets, in a circular path.

This is relatively simple to explain, because the superconductor generates a magnetic field that opposes the field applied by the magnets and this keeps it suspended.

But, the next thing she did was to turn the table upside down so now the puck was hanging under the table and following the same circular path.

If the magnetic effect was purely a repulsive one, the puck would have fallen to the floor. Instead it hangs there; so it seems to be both attracted and repelled from the surface at the same time.

How?

I'm not sure because I should think a little bit more about it so this is my answer version 1.0  []
When you make the superconductor (SC) puck approach the disk of magnets from the above, an induced current is formed on the first, because of Lenz's law this current is such to create a magnetic field on the SC puck which is (perfectly) opposite to the other field generated from the magnets, as you wrote.

But what would happen if, in this situation, you tried to pull up the puck?
Exactly for the same reason, inside the puck would be generated a current which generates a magnetic field in the opposite sense with respect as before, which would make the puck be attracted, this time, from the magnets, showing a resistance to be pulled up.

When the puck+magnets are upside down, the puck's weight pulls it downward and this, for what I wrote, generates a resistance to fall, that is a magnetic force which prevents it to fall down.

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Physics, Astronomy & Cosmology / Re: gravitational waves: sould we be skeptic about their practical importance?

« on: 01/03/2016 13:24:27 »

The importance is that they have been detected albeit as a unique coincidence of two black holes merging and the engineering science to build a detector being implemented exactly 1.3 billion years later.

No, it's not such a coincidence: the detectors were built after precise calculations (made also from Kip Thorne, if I remember correctly) about the statistical number of such events in the radius of action of the detector itself, they found those devices would have a non zero probability to detect such kind of events in a year.

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Physics, Astronomy & Cosmology / Re: gravitational waves: sould we be skeptic about their practical importance?

« on: 01/03/2016 13:17:24 »

Could it allow us to detect rogue black holes, which are thought to be drifting through space, invisible to us?

Could it allow us to detect alien spaceships using curvature propulsion?  [] [] []

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Physics, Astronomy & Cosmology / Re: Can 2 photons be in the same place at once?

« on: 29/02/2016 11:47:10 »

It's as stating that an ant on Earth and another on Pluto follow the same path since they are both in the solar system...

I would rather say that an ant in an ant tunnel, and another ant in the same tunnel follow the same path because they are both in the same tunnel.

But stating that the entire wavefunction of the photons (which don't have a wavefunction  []) is spread inside all of the tunnel/optical fiber it's exactly the same as stating that the photons don't have a precise location at all. If you want to talk about them as "localized corpuscles" then you have to treat them as points with zero dimensions, because when they are detected they don't have any measurable non-zero extension.
But if they are points, then they are infinitelly smaller than any finite diametre of an optical fiber. This is the sense of the comment I made in my previous post. It's analogous to the path of an electron in a bubble chamber: the existence of such a path doesn't mean that the electron have a precise trajectory, since the path's transversal dimensions are much greater than the electron's (almost point-like) dimensions.

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Physics, Astronomy & Cosmology / Re: Can 2 photons be in the same place at once?

« on: 27/02/2016 08:00:19 »

Could they even travel an identical path simultaneously?

The core of single-mode optical fiber is just wide enough for an infra-red photon to pass along the center. So all photons follow the same path through the fiber.

It's as stating that an ant on Earth and another on Pluto follow the same path since they are both in the solar system...

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Physics, Astronomy & Cosmology / Re: Can 2 photons be in the same place at once?

« on: 26/02/2016 08:34:15 »

Since photons are considered massless does this mean that 2 of them can occupy the same space at the same time? Could they even travel an identical path simultaneously?

Two photons can have the same exact location on a detector only, because from source to detector they don't have an exact location at all.

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Physics, Astronomy & Cosmology / Re: Does pi stand for "perfectly incomplete" ?

« on: 09/02/2016 18:56:47 »

About the number π: it's *a number* (a real number, more precisely irrational) as it is sqrt(2), for example, and so it has no need to be defined in terms of geometry (about the ratio of diameter to circumference of a circle: it's the number π only in euclidean geometry; in other geometries that ratio is other numbers) and has with physics the same relation that has any other number, excepting the fact it's more used than others.

π could be defined as other real numbers (like the number "e") are defined, with an infinite series, e.g.:

π = sqrt(12)∑{k=0, k=∞} (-3)^-k/(2k+1)

https://en.wikipedia.org/wiki/Approximations_of_%CF%80

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Physics, Astronomy & Cosmology / Re: Does pi stand for "perfectly incomplete" ?

« on: 09/02/2016 18:33:56 »

pi=perfectly incomplete
even a perfect circle has no symmetry:  3.14159265359... ∞
the uncertainty principle in physics and godel’s incompleteness theorem in math is a reflection of pi itself,
...

Just a question: did you take phrases at chance and pasted them together?

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Physics, Astronomy & Cosmology / Re: Photons and the Speed of Light.

« on: 04/01/2016 16:26:05 »

Oh, I've heard some people say, photons have energy, but no mass. But that is ridiculous. Einstein showed energy is mass. And mass is energy. So there.

No way! Einstein *has not* showed that. He has showed that a body which has energy E in a frame of reference where it doesn't move has also mass m related to it:
E_{(measured in a frame where body doesn't move)} = mc²

You are just the billionth person which has been deceived about it from popular books.  []

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Physics, Astronomy & Cosmology / Re: What's the difference between general and special relativity?

« on: 11/12/2015 13:07:17 »

Lightarrow,

So, for example, in absence of massive objects or others which can warp spacetime, we can use SR even to treat accelerating spaceships,

We can't use SR to teat accelerating spaceships.

Guess why I have specified that? Because your is a common mistake.

SR works with non-accelerating reference frames. Constant velocities. As such it is a good way to demonstrate and explain relativistic effects.

And were I wrote that you have to work in the accelerated reference frame? You have a spaceship accelerating with respect to an inertial reference frame and you make your computations in that inertial frame.

Real life situations are a bit more complicated than that and that's where General Relativity is used.

But you can't invoke the equivalence principle in the sense that spacetime does not become warped only because you are in an accelerating (instead that inertial) frame: the spacetime stays the same (if that is what you intended to say).

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