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Physics, Astronomy & Cosmology / Re: Does gravity attract masses in space, or does it curve space between them?

« on: 26/05/2020 11:24:09 »

[That is interesting.Could you expand on that at all?
How would a uniform gravitational field manifest its quality of producing no spacetime curvature?

There is no spacetime curvature in a uniform gravitational field. It's a myth that all gravity is a curvature in spacetime. Curved spacetime is the same thing as tidal forces and a uniform gravitational field has no tidal forces.

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Physics, Astronomy & Cosmology / Re: Do the electrons that generate an electric current come from the wire's atoms?

« on: 13/01/2020 18:09:40 »

Rakesh reached out with a couple of questions on electric current:
What is the speed of electric current? When elections flow - do they come out from the atoms and flow as electric current? Is it not true that when electrons come out from atoms, light and energy is released? So why don't electric wires change their color?
Can you help?

The electrons in a conductor exist in sea of electrons. They aren't bound to particular atoms.

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Physics, Astronomy & Cosmology / Re: Is earth moving at close to the speed of light?

« on: 25/04/2019 08:59:42 »

Since motion is relative then in some frames of reference we can be considered to be moving close to the speed of light. Are we actually moving at close to the speed of light?

The question is incomplete. You need to ask "are we moving near the speed of light in as measured in frame S." where S is specified by the person asking the question. In our frame (sitting on earth) the answer is no.

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New Theories / Re: Can a photon be visualized ?

« on: 10/04/2019 12:39:19 »

Can you confirm c is the same for everyone under GR and SR relatively speaking. I am not aware of any experiments indicating c is variable in a gravitational field.

Experiments in the 1960's by Irwin Shapiro confirmed what Einstein predicted, i.e. that c is variable in a non-inertial frame, i.e. a gravitational field.

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New Theories / Re: Can a photon be visualized ?

« on: 08/04/2019 01:16:34 »

Please correct where I am wrong.

Maxwells equations describe the classical view of electromagnetic waves.

A single photon can be viewed as a quantum particle.

Its not possible to state whether a photon is a particle or a wave unless you state how its observed. That's the essence of the wave-particle duality.

Note that the Schrodinger equation only holds for non-relativistic particles and photons are relativistic particles.

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Physics, Astronomy & Cosmology / Re: What is an "event" ?

« on: 19/03/2019 10:18:45 »

I am interested in anything you have to say, so if it is no bother if you have the Peebles text on Cosmology easily to hand, I would be interested to see what he has to say.

From Principles of Physical Cosmology by Peebles, page 6

The familiar name for this picture, the "big bang" cosmological model, is unfortunate because it suggests we are identifying an event that triggered the expansion of the universe, and it may suggest the event was an explosion in space. Both are wrong. ... If there were an instant, at a "big bang," when our universe started expanding, it is not in the cosmology as ow accepted, because no one has thought of a way to adduce objective physical evidence that such an event occurred.

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New Theories / Re: How do we measure the energy of a photon?

« on: 20/02/2019 00:34:22 »

You might find a discussion more to your taste in a forum devoted to New Age thinking or even metaphysics

Condescending! You asked me for my definition of energy. I gave it:).

The definition is on my website at
http://www.newenglandphysics.org/physics_world/cm/what_is_energy.htm

Its what Feynman used in his Lectures.

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Physics, Astronomy & Cosmology / Re: What field gives rise to the Van Der Waals forces?

« on: 17/02/2019 18:41:09 »

Since forces can be associated with fields I am wondering what this one is.

The electric field. Is caused by both intermolecular attraction and electron cloud repulsion. Best to look it up in a chemistry text for a solid description.

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Physics, Astronomy & Cosmology / Re: How many black holes are there in the Universe?

« on: 07/10/2018 03:01:48 »

There seems to be no controversy (in Science) with respect to the existence of the Black Hole. My question:

Is there more than one Black Hole in the Universe?

Sure. In fact in this galaxy alone there could be a million of them.

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Physics, Astronomy & Cosmology / Re: Can the vacuum be affected by gravity?

« on: 23/09/2018 05:04:15 »

Yes. Recall Hawking Radiation.

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Physics, Astronomy & Cosmology / Re: How can a universe start from nothing?

« on: 29/08/2018 13:38:20 »

Accelerating objects radiate.

Only charged particles radiate, unless you're talking about gravitational waves?

Place a charged particle on the floor so that its at rest. Now choose a frame in free fall. In that frame the charge is accelerating so it will radiate. But no radiation will be detected in the rest frame of the charge. Its relative.

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Physics, Astronomy & Cosmology / Re: How can a universe start from nothing?

« on: 26/08/2018 21:30:05 »

m×c² – 2×G×m×M/r = 0  (we have to count the gravitational term twice because each body exerts on the other, I think...)

I disagree. The potential energy is for the system of two particles in this case so you don't need the two.

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Physics, Astronomy & Cosmology / Re: Does hot air gain potential energy when it rises?

« on: 04/08/2018 20:53:35 »

Temperature is a form of kinetic energy (largely), and therefore we would expect a mass of warm air to cool as it rises, as the kinetic energy of its temperature gets exchanged for potential energy of its height (and this is typically what is observed).

Excellent response. My compliments to the chef!

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Physics, Astronomy & Cosmology / Re: Why is energy observer dependent?

« on: 24/06/2018 13:15:33 »

This states that L = V + U.

Correction. L = T - V, where T = Kinetic energy and V = Potential energy. If the potential is a velocity dependent one then the letter U is used. This is particularly important in electrodynamics.

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Physics, Astronomy & Cosmology / Re: Efficiency of light as energy source?

« on: 22/06/2018 10:02:07 »

Light already is energy.

Not very useful as electricity.

Light isn't energy. It has energy. Big difference.

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New Theories / Re: Was a white hole the source of the Big Bang?

« on: 10/06/2018 21:12:32 »

What part of differential geometry do you suspect I do not understand. I assume you talking about grads divs and curls

No. That's vector calculus. The basics of differential geometry are described here:
http://www.newenglandphysics.org/physics_world/ma/ma.htm

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Physics, Astronomy & Cosmology / Re: Is there such thing as inertial rotation?

« on: 07/06/2018 13:09:14 »

I pulled out my old undergrad text by Haliday and Resnik and looked it up to be certain. It is called "rotational inertia" and represented by I just like mass is represented by M. The cool think is that they have similar expressions for kinetic energy. In general I is a tensor.  But in many cases it can be written using a scalar. In that case the rotational kinetic energy = (1/2)I*omega^2   where omega is the angular speed. Look familiar?  Sort of like K= (1/2) M*v^2

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Physics, Astronomy & Cosmology / Re: Is there such thing as inertial rotation?

« on: 07/06/2018 01:05:59 »

So that unless acted on by an external force an object would continue rotating with a constant angular velocity.

Yes. It's referred to as rotational inertia and can be calculated. Look it up in Wikipedia.

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Physics, Astronomy & Cosmology / Re: If nothing is faster than light, how can we look back in time with a telescope?

« on: 25/05/2018 21:27:27 »

Thanks folks for the answer  to my original question.

I get the super nova example but not the- We don't "look back" to the big bang as if it happened a long distance away. In a sense it happened everywhere..... HELP!!!!

The term "big bang" is misleading. It makes it appear as if within the theory itself there is an event which started the universe expanding. There may have been such an event but we have no way to adduce it as of now.

About the big bang being everywhere: Space is not as simple a thing as you may have thought. The big bang is not a theory about something which exploded and sent material whooshing out from a specific point in space. Its about the notion that its space itself which is expanding. A commonly used analogy is to imagine a bunch of two dimensional beings who are sitting on the surface of a balloon and as he balloon expands and gets larger, each being on the surface sees the everyone else moving away from them. They might even conclude that where they sit the expansion started at their position because everything is moving a way from their location.

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Physics, Astronomy & Cosmology / Re: If nothing is faster than light, how can we look back in time with a telescope?

« on: 25/05/2018 10:11:14 »

This, from Stephen Whiston - @whizzer666 - on Twitter today:

"I have always not been able to reconcile the fact - nothing is faster then the speed of light - yet we look back to the big bang through our telescopes - honesty how does that work? Can you explain?"

Who can help with this?

We don't "look back" to the big bang as if it happened a long distance away. In a sense it happened everywhere.

As far as looking into the past we do it all the time. It takes light and sound a finite time to travel the two or three feet between two people having a conversation. In that sense we're communicating with others in the past. In fact most of what we actually experience occurred in the past.

Evan - The atomic mass becomes before the chemical symbol, not after it. I.e. What you wrote., i.e. Fe⁶⁰ should be written as ⁶⁰Fe.