101

Physics, Astronomy & Cosmology / Re: Do matter and antimatter interact gravitationally?

« on: 01/05/2016 18:01:14 »

Pmbphy, if i understand we assume that inertial mass is the same thing than gravitational mass, so antimatter should fall the same, right?

Right. That holds for all particles. There's no reason to expect a positron (the antiparticle of the electron) to fall at a different rate than anything else. However, if, for some bizarre reason, certain particles fell at different rates than 9.8 m/s^2 then general relativity would have to be modified.

I am sorry i do not understand the second part, what is arbitrary?

What is arbitrary is which particles are referred to as normal "particles" and which particles are referred to as "antiparticles." For instance the positron is said to be the antiparticle of the electron. It's also true that the electron is the antiparticle of the positron. So which particle is defined to be an "antiparticle" is completely arbitrary. The choices made as to which is which came about due to historical reasons only.

Here is the way that Dr. Matt Strassler explains it. From: https://profmattstrassler.com/articles-and-posts/particle-physics-basics/

There are many confusions about antiparticles. You cannot look at an object and say whether it is a particle or an anti-particle; you can only say X is an anti-particle of Y, and so Y is an anti-particle of X. You can’t say Y is the particle and X is the anti-particle, or vice versa.

I highly recommend reading the rest of what he wrote. It's quite educational and very well written.  Anyway, that is precisely what I meant when I said In fact there is no distinction between a particle and its antiparticle, this convention is arbitrary. Most people don't know about this.

Another common misbelief about antimatter is particle/antiparticle annihilation. It appears that most layman, even some professional physicists, believe that when a particle is near its antiparticle the two will annihilate and yield only photons. That's wrong.

102

Physics, Astronomy & Cosmology / Re: Do matter and antimatter interact gravitationally?

« on: 01/05/2016 12:16:49 »

Hello everyone, they are currently different experiments in the CERN to see how antimatter behave with the gravitational field of our Earth, i was thinking, what if they do not find any gravitational interaction between matter and antimatter?

That's quite an odd experiment. The inertial mass of a particle is identical to the mass of that particles antiparticle and since inertial mass equal gravitational mass there is no reason to believe that an antiparticle should fall at a rate which is different than its counter particle. In fact there is no distinction between a particle and its antiparticle, this convention is arbitrary. Which particle is referred to as the particle and which is referred to as the antiparticle is merely a matter of convention.

Would it be possible then that matter attracts matter, antimatter repulses antimatter, with no gravitational interaction between them.

No, because its not possible to consider a particle and determine if its an antiparticle or not. The only thing possible is to compare it with other particles and if one particle has all of its defining constants such as its mass, charge, spin, baryon number, etc. opposite to it then you have a particle/antiparticle pair. Which one you refer to as the antiparticle is arbitrary.

103

Physics, Astronomy & Cosmology / Re: What is a tensor?

« on: 25/04/2016 23:40:37 »

Could someone provide a practical description of tensors of first & second order, etc.?  Trying to get this relativity thing (A.R., Absolute Relativity is looking good) & i'm hitting a roadblock with my limited understanding of differential linear algebra.

Thanks in advance...

A tensor is typically defined in two equivalent ways. One way is what I refer to as the geometric definition. The second way is what I refer to as the analytic definition. I created two webpages to explain these in detail for each viewpoint.

Geometric definition: A tensor is defined as a multi-linear map from vectors and 1-forms to the set of real numbers. See:
www.newenglandphysics.org/physics_world/math_phy/05_tensors_via_geometric/tensor_via_geometric.htm

Analytic definition: An equivalent way of defining a tensor, one commonly used in relativity, is a set of numbers which transform from one system of coordinates to another by a certain transformation rule. See:
http://www.newenglandphysics.org/physics_world/math_phy/04_tensors_via_analytic/tensors_via_analytic.htm

104

Physics, Astronomy & Cosmology / Re: Do particles actually exist?

« on: 23/04/2016 01:23:15 »

We observe events compelled by fields; don't we?  Has anyone actually seen a particle?  Do we need duality or, are self-propigating waves enough?

Neither particles nor fields can be "seen".

I'll assume that you're speaking of elementary particles such as electrons, neutrinos, photons, etc. The term particle is often used to refer to objects whose dimensions are small enough to be considered negligible for the purpose at hand. E.g. we use the particle approximation when we calculate the orbits of planets and satellites.

In science we don't typically use the term exist. What we do is make observations and using logical induction formulate postulates from which we can generate theories. Starting with these postulates as premises we can then use logical deduction to arrive at proofs which can then be tested in the lab. If these observations are confirmed the lab then the we say that those postulates the postulates have gained support. Otherwise the postulates are either wrong. The theory then needs to be modified or tossed out.

The concept of particle that you're speaking of has an overwhelming amount of of experimental support. However there are those in the physics community who hold that particles don't exist and that only fields exist. I've seen this idea published in the American Journal of Physics, one of the most highly respected physics journals that there is. Then again another article in the same journal which holds that neither particles nor fields exist (what's a person to do? Lol!!)  The references for those articles are

There are no particles, only fields by Art Hobson, Am. J. Phys. 81, 211 (2013)
http://scitation.aip.org/content/aapt/journal/ajp/81/3/10.1119/1.4789885
You can download this from: http://arxiv.org/abs/1204.4616

There are no particles, and there are no fields by Robert J. Sciamanda, Am. J. Phys. 81, 645 (2013)
http://scitation.aip.org/content/aapt/journal/ajp/81/9/10.1119/1.4812316
physics.uark.edu/hobson/pubs/13.09.a.AJP.pdf

105

Physics, Astronomy & Cosmology / Re: What is the weight felt by a person in freely falling lift ?

« on: 22/04/2016 15:52:16 »

It's zero []  But I don't know how scientifically.Can someone explain this to me?

The weight of an object can be and is defined in two ways;

1) the force due to gravity on a body
2) the force required to hold a body at rest, i.e. to prevent it from falling, in a gravitational field.

Let's use the second definition since most of us think that way. When you're in free fall there are no forces other than gravity acting on your body. The force of gravity is not something you can feel when you're in free fall because it causes every single particle in your body to fall at exactly the same rate. In your frame of reference, i.e. the frame in free fall, there is, for all practical purposes, no gravitational field. In fact in general relativity there really isn't a gravitational field in a free fall frame. It's said to have been transformed away.

Was that helpful?  []

106

Physics, Astronomy & Cosmology / Re: How does earth exert same acceleration on all kinds of objects ?

« on: 21/04/2016 06:06:25 »

Would it hurt to tell H.S. students that in Newtonian theory this is a coincidence; gravitational mass & inertial mass are equal for some as yet unknown reason: in G.R., inertial mass & gravitational mass are asserted to be equal, indistinguishable; they could handle that, eh?

Sure. Of course they can handle it. Never make the mistake that high school students aren't smart. When they ask questions like this it's to learn the answer. That means they're climbing out of a state of ignorance using their inherent intelligence.

By the way. This isn't true just in Newtonian mechanics but also in GR. In both theories its an experimental fact. It's the reason why particles move on geodesics.

107

Physics, Astronomy & Cosmology / Re: Why don't an atom's electrons fall into the nucleus and stick to the protons?

« on: 08/11/2015 09:06:55 »

Well that was unexpected and interesting.

After this post became inactive I found a webpage which explains it wonderfully. It's not as if I don't know the answer to the question but other people are so much better at explaining things to other people. Here's that page:
http://www.chem1.com/acad/webtut/atomic/WhyTheElectron.html

What's on that page you have you have

108

Physics, Astronomy & Cosmology / Re: Can a photon be length contracted?

« on: 05/11/2015 13:53:14 »

Can the concept of length contraction be applied to photons? If not then why not?

In addition to the above comments you should also take note that no elementary particle that has a non-zero proper mass undergoes Lorentz contraction because it has no dimensions because its radius is zero and L/gamma = L for all point particles having non-zero proper mass.

109

Just Chat! / Re: What do we think of the medals next to your name?

« on: 30/10/2015 15:46:11 »

I like it.

110

Physics, Astronomy & Cosmology / Re: What is the largest possible rest mass of the photon?

« on: 30/10/2015 15:41:56 »

The largest possible mass which is consistent with the experimental data that we have is 4x10^-51 kg. This is the value stated in Classical Electrodynamics - 3rd Ed. by J. D. Jackson, page 7.

111

Physics, Astronomy & Cosmology / Re: Is intergalactic space magnetised?

« on: 28/10/2015 03:41:02 »

But surely the only reason that charged particles will move is if there is an electro-magnetic or electro-static force pulling them forward.

I don't understand this comment. You're acting like there has to be a force on a particle in order to make it move. Surely you're aware of Newton's first law. See: https://en.wikipedia.org/wiki/Newton%27s_laws_of_motion#Newton.27s_first_law

The first law states that if the net force (the vector sum of all forces acting on an object) is zero, then the velocity of the object is constant.

That means that if a body is in motion then it will stay in motion unless acted upon by a force.

Regarding galactic magnetic fields: I was quite surprised to find this online. See: http://www.scholarpedia.org/article/Galactic_magnetic_fields

Magnetic fields are a major agent in the interstellar medium (ISM) of spiral, barred, irregular and dwarf galaxies. They contribute significantly to the total pressure which balances the ISM against gravity. They may affect the gas flows in spiral arms, around bars and in galaxy halos. Magnetic fields are essential for the onset of star formation as they enable the removal of angular momentum from the protostellar cloud during its collapse.

Thanks for asking this question. Otherwise I'd never have know about this! I love it when I'm properly proved wrong. []

112

Physics, Astronomy & Cosmology / Re: Could you become a God by traveling at the speed of light?

« on: 27/10/2015 11:16:57 »

... and what you mentioned about space being god i tried to look that over but i couldn't find a reference for it could you provide me with a reference please thanks for your comment i found it to be refreshing  []

It's well known by Einstein historians and those who are knowledgeable of Einstein's religious beliefs that he was a pantheist. Pantheism is defined here: https://en.wikipedia.org/wiki/Pantheism

Pantheism is the belief that the Universe (or nature as the totality of everything) is identical with divinity,[1] or that everything composes an all-encompassing, immanent god.[2] Pantheists thus do not believe in a distinct personal or anthropomorphic god.

So in a very small way "the box" is partially correct.

113

Physics, Astronomy & Cosmology / Re: Could you become a God by traveling at the speed of light?

« on: 25/10/2015 09:21:56 »

Not only is your theory wrong but you posted it in a place where you're not supposed to post "new/personal" theories. There's an entire subforum whose purpose is just that. Go to:
http://www.thenakedscientists.com/forum/index.php?board=18.0

114

Physics, Astronomy & Cosmology / Re: Is gravitational motion perpetual?

« on: 24/10/2015 18:23:46 »

The question is a little misleading. If we have a perfect sphere with a perfectly frictionless surface and set in motion an object along this surface would its inertia be changed by gravity.

What do you man by its inertial changing? Inertia refers to the mass of a body so I can't see how a body sliding along the surface of a sphere would change. What made you think it would?

That is would gravity eventually stop the motion of the object? Take the mass of the sphere as being the same as that of the earth.

In general relativity one can show that the system will emit gravitational waves which carry off energy and thus the motion will eventually cease. But that would take an extremely long time to happen. However using Newtonian gravity there is no reason that motion will ever change.

115

Physics, Astronomy & Cosmology / Re: Is intergalactic space magnetised?

« on: 23/10/2015 16:02:18 »

Where is your proof that galaxies are not magnetised.  All the evidence surely is that they are?

I don't like answering these kinds of questions anymore because almost always it is not that worthwhile to pursue ideas like these.

First of all it's not meaningful to speak of space as being magnetized in the sense that you used it here. See:
http://www.thefreedictionary.com/magnetized

Magnetized: to make magnetic.

You seem to be saying that the entire galaxy is a magnet which we know to be false.

In the second place, you're quite wrong in that (1) there is no evidence for the existence of such magnetization and (2) like Chris explained you can't have magnetization with nothing which is causing it to magnetize. Not to mention that it would also destroy the symmetry of space. I.e. if there is a magnetic field everywhere then in what direction is it pointing?

Think about it. If the galaxy was magnetized then everywhere you go, even in your bedroom, there would be a magnetic field other than that of the Earth's since the magnetic field around the Earth has been measured we know that the only field there is due to the Earth itself. Solar winds are streams of charged particles. If the universe was magnetized then no solar wind would ever reach the Earth. Those particles would go into orbit around the Sun, loose energy and then spiral back into the Sun. The existence of the Van Alan belt proves this not to be the case.

Regarding your request about proving that "galaxies are not magnetized" you should know that the science of physics is not about proving things. It's about running experiments and making observations to confirm things are as theorized. If not then the theory is wrong, etc.

See The science of physics is not about "proving" anything by Alan Guth at:
http://www.newenglandphysics.org/common_misconceptions/DSC_0002.MOV

And dark matter isn't just found in galaxies, its been hypothesized to be everywhere in the universe. See:
https://en.wikipedia.org/wiki/Dark_matter

Dark matter is a hypothetical kind of matter that cannot be seen with telescopes but would account for most of the matter in the universe.
....
Structure formation (https://en.wikipedia.org/wiki/Dark_matter#Structure_formation)

Dark matter is crucial to the Big Bang model of cosmology as a component which corresponds directly to measurements of the parameters associated with Friedmann cosmology solutions to general relativity. In particular, measurements of the cosmic microwave background anisotropies correspond to a cosmology where much of the matter interacts with photons more weakly than the known forces that couple light interactions to baryonic matter. Likewise, a significant amount of non-baryonic, cold matter is necessary to explain the large-scale structure of the universe.

116

Physics, Astronomy & Cosmology / Re: Is intergalactic space magnetised?

« on: 23/10/2015 09:54:10 »

If space is magnetised then the stars inside a galaxy will all rotate in a uniform pattern. Have just read an article by BryanG that demonstrates that even old galaxies are magnetise as is proven by the fact that light passing through them is polarized. 
If this is the case then stars will be forced to rotate magnetically and the need for dark matter will disappear.  See  http://dunlap.utoronto.ca/~bgaensler/papers/stories/301Gaensler-3.pdf

That idea is badly flawed. Even if space was magnetized, which it isn't, then it wouldn't cause a stars orbital speed to increase. It wouldn't even cause its rotational speed to increase.

117

Physics, Astronomy & Cosmology / Re: If an object is moving through space and no force is applied, where does it go?

« on: 19/10/2015 03:35:00 »

Hi all, is it true that an object set into motion in outer space will travel in a straight line until a force alters it's direction? If the object never meets another force where will it end up?

Simple. Just apply Newton's First Law. A body which is at rest remains at rest and a body which is motion will remain in motion unless its affected by by an external force.

118

Physics, Astronomy & Cosmology / Re: Are there more stars in the Universe than grains of sand on Earth?

« on: 18/10/2015 00:11:23 »

Hi all,  a friend told me that there was more stars in the universe than there are grains of sand on the whole planet! Is this correct? If that were true just how many planets and moons would we be talking about?

If the universe is flat then yes, that's true. If it's not true then it might still be true, I don't know.

119

New Theories / Re: what causes gravity??

« on: 13/10/2015 10:34:26 »

Hi Kenyonm. Welcome to the forum!  []

The earth hasn't always been spinning, its rotation is relative to it's size, so as it grew in it's beginning stages, the rotation increased until the earth solidified and its mass became static.

The Earth used to rotate faster than it does now. Tidal forces caused by the moon is causing the rate of rotation to slow down.

Why does it rotate ?

If it didn't, the forces in the unviverse would pull it apart and it would spread out like compressed gas does when it is released into air.

There are no forces in the universe which would pull the Earth apart. The only force acting on the Earth are gravitational forces from other bodies. They can basically be ignored since they're pretty small. The force on the Earth by its own forces hold it together. In fact that's what gives the Earth the shape of a sphere. But it  wouldn't be pulled apart by other forces in the universe.

The rest of the milky way, our galaxy, is pulling the earth in ever changing directions as the concentrations of stars in the galaxy line up to concentrate the pull in all directions unevenly.

The magnitude of those forces on the Earth are so small that they can be neglected for all intents and purposes.

Now to the subject of gravity.

Speaking of which. Sir Arthur Eddington wrote the following about Einstein's theory of gravity, i.e. General Relativity

The purpose of Einstein's new theory has often been misunderstood, and it is criticized as a attempt to explain gravity. The theory does not offer any explanation of gravitation; that lies outside its scope, and does not even hint at a possible mechanism. It is true that we have introduced a definite hypothesis as to the relation between gravity and a distortion in space; but if that explains anything, it explains not gravitation, but space, i.e. the scaffolding constructed from our measures. - A.S. Eddington, Nature, March 14, 1918, page 36

We were once fish and existed as fish do without any gravitational force on us. The word Gravity is a word we have come up with for something we do not understand, when we do fully understand it we will not call it this anymore.

That's quite wrong. We call it gravity because we merely needed to give the phenomena a name like we do with everything else in nature.

..., when we do fully understand it we will not call it this anymore.

That has never been true. I.e. there has never been a phenomena which was given a name and then given another name when we "fully understood" it. In fact there will never be a time in the future where we can say that we know everything about something, i.e. we will never "fully understand" anything. That's not one of the abilities in science.

See something which is closely related at: ttp://www.newenglandphysics.org/common_misconceptions/DSC_0002.MOV

So newtons law does not follow here, the gravitational force on the fish mass x the acceleration due to gravity g. This = 0  g=0 when the density of the object is the same as the medium.

You're wrong. Newton's law of gravitation always applies in its domain of applicability such as is the case here. There is a force of gravity acting on the fish and another force exerted on the fish due to the water pressure surrounding the fish. The forces cancel out.

etc.

120

Physics, Astronomy & Cosmology / Re: Does Einstein's equation E=MC^2 negate the idea of no travel faster than light?

« on: 05/03/2015 15:05:08 »

PmbPhy, do you have any ideas on how we can warp space time?

Matter curved spacetime.

This is a forum for free thought right?

Yes. So long as this is what you think that means: http://en.wikipedia.org/wiki/Freethought