1

Famous Scientists, Doctors and Inventors / Will I post a link for some new Feynman videos here?

« on: 02/04/2021 17:00:38 »

http://www.thescienceforum.com/links/50272-newly-presented-feynman-lectures.html

I like them a lot  since they are good quality and maybe this is a good place to post a link to them?

https://www.feynmanlectures.caltech.edu/

2

Physics, Astronomy & Cosmology / How does mass-energy curve spacetime?

« on: 19/02/2021 04:24:43 »

I am fairly sure,based on what I have heard that the answer is that we do not yet know the answer to this.

However ,are there any serious ideas as to what the actual mechanism might be ?

I imagine it might be somehow based on  fields  since that seems to be the predominant area of theory concerning very small object's,which may be the level where spacetime curvature occurs.

But I have extremely little insight into this area.

Are there any theories or hypotheses that could make some sort of sense to a layman?

3

Physics, Astronomy & Cosmology / What happens to the spacetime interval between two events as they approach a BH?

« on: 17/02/2021 16:13:28 »

....or any similar object that curves spacetime?

ie how does the r/t ratio in the s^2= ct^2-r^2  formula change?

Edit :I don't mean the same event ,of course .I mean  identical events whose spacetime intervals are measured as they approach the source of gravity.(Perhaps  light reflecting between two mirrors would do - or two hypothetical events involving massive objects)

Reedit: the event pairs  are causally connected.

4

Physics, Astronomy & Cosmology / Are there any serious ideas floating around about Wormholes?

« on: 21/12/2020 14:38:31 »

I have heard that they could be a consequence of intense gravitational environments where the spacetime curvature "shears" in some way.

Are there any coherent ideas going the rounds as to what consequences might follow if this idea had any firm basis and was able to be verified in some way?

What might observers of the sky be on the look out for example?

Something enormous?. Something tiny ? In between?

5

Physics, Astronomy & Cosmology / What is the smallest theoretical magnet?

« on: 14/12/2020 01:16:48 »

I see that a single atom can be described as a magnet,

https://phys.org/news/2017-03-ibm-world-smallest-magnet.amp


Is it possible to go smaller?

What if two (or 3?) individual  electrons interact with each other?

Do they create a magnetic field?

Can one group of electrons be considered as a "magnet" to the other ,single electron?

Does the interaction of 2 or more electrons always (ever?) produce em radiation?

6

Physics, Astronomy & Cosmology / How does light move in a vacuum?

« on: 27/11/2020 15:54:34 »

I understand that em waves propagate as disturbances in the em field (correct?)as an expanding sphere centred on the point of emission.

What is the actual mechanism that causes this propagation effect?(I "know" that the electric field  creates a magnetic field and vice versa)

Is it connected to the action and reaction effect that allows rockets to move in a vacuum?

Is it valid to ask what happens if there is no pre-existing em field for the  wave to propagate through?

Would that be nonsensical ?

7

Physics, Astronomy & Cosmology / What is a small classical example of em radiation?

« on: 22/06/2020 14:24:01 »

 I am trying to find an example of an extremely small electric charge moving wrt to  a magnetized conductor and causing  a photon to be created.

I understand that this can be seen as a classical or as a quantum phenomenon and so I would like to understand it classically in as microscopic a way as possible and then to try and understand it in the Quantum explanation (although I anticipate this as  being very challenging  for me)

8

Physics, Astronomy & Cosmology / Is the equivalence principle only approximately correct?

« on: 11/01/2020 00:44:27 »

I have been reading E's Popular Exposition of SR and  GR (it is for the layman and so I may be reading too much into what may be relatively simplistic scenarios) and the following "objection" to his closed room experiment occurred to me.
The gist of his argument seems to be that an observer in a sealed container  will not be able to tell if he or she is being accelerated or experiencing gravity.

However  ,if the propulsion is being caused by a rope tugging a hook in the centre of the ceiling it would be possible by  examining the ceiling to verify that the force is in fact being directed at that particular area (the room cannot be 100% rigid) and so it is possible to distinguish between a gravitational  effect vs acceleration.

If the room was vanishingly small (Or completely rigid) this would indeed  then be impossible.

Am I right or just being pedantic? (Or misunderstanding the scenario in the round?)

9

Physics, Astronomy & Cosmology / When did gravity begin?

« on: 14/12/2019 00:45:14 »

Did the first (and only?)  gravity field start very soon after the BB?

Was it "kick started" by the Higgs field?

10

Physics, Astronomy & Cosmology / Is the vacuum synonymous with the absence of a medium?

« on: 06/11/2019 00:46:19 »

Is that all the vacuum is?
And are there mediums that have properties that are closer to those of a vacuum than others?

If you "rarify" any medium does it approach a vacuum as a limit?

So a vacuum in that sense is ** a kind of medium ,especially since it is said that it is probably not empty?

** Well at least  is not the opposite of a medium

11

Physics, Astronomy & Cosmology / Can we say that we "fall through spacetime"?

« on: 30/10/2019 11:22:15 »

If we can say this ,I am intrigued by the notion of "falling".

When we "fall" towards Earth (or any massive body) are we also "falling through local spacetime"?
Also,do we also fall through spacetime  when no massive bodies affect our movement?

Would  this concept apply to the twin "paradox"? Do both twins "fall" through the same spacetime interval but follow ("fall through"?) different paths?

Could  two hosepipes  with ends that meet at beginning and end serve as anything like a useful analogy?

12

Physics, Astronomy & Cosmology / Does the invariance of c have a role in the theories around Inflation/Expansion?

« on: 29/09/2019 15:25:15 »

I suppose I am really thinking of Inflation as it seems more fundamental.

How far back in the "genesis" of U does Inflation attempt to go and does it involve a role for c?

13

Physics, Astronomy & Cosmology / Special Relativity without Light

« on: 19/09/2019 17:00:32 »

https://arxiv.org/pdf/physics/0302045.pdf

I have been working my way through this approach for a while now (have come back to it 3 or 4 times ) and am getting stuck at this point

Using Eqs. (9) and (10), we obtain
X(x2 + h, t, v) − X(x2, t, v) = X(x1 + h, t, v) − X(x1, t, v). (11)

Dividing both sides by h and taking the limit h → 0, we obtain ∂X /∂x ¦ x2 = ∂X/ ∂x¦ x1   (12)

Apologies for the poor formatting ,copy and paste  comes up short here.


Can anyone help me through this tricky bit?
The author says he is dividing by h  but the result of the partial differentiation (that is what he is doing?) seems to be a division by x .

My partial differentiation skills are rusty and it would take me a lot of work to bring them up to scratch...

What about the article as a whole?Does anyone find it interesting?

He goes on to say that   "Thus, the function X(x, t, v) must be a linear function of x"

Can anyone clarify that particular point as well?

14

Physics, Astronomy & Cosmology / Can we talk about a "Speed of Causality"?

« on: 01/07/2019 11:39:44 »

I am guessing that we can't and that "speed" comes into the equation when the method of effecting change or exchanging information   is taken into account.

Causality itself seems to me to be perhaps  more fundamental than the maximum speed limit in a vacuum and perhaps all that can be said (well by me) is that it goes in one direction ?(even that with apparent caveats since there may be a non zero possibility that it may not on occasion)

(Is there even a non zero possibility that it doesn't even move at all on occasion? )

edit the part  I have underlined in red  I am on reflection very unsure of  and think that I may just have misremembered it.

Perhaps all I have heard is that the direction of time  may be immaterial at the quantum level         

15

Physics, Astronomy & Cosmology / Is "Space" distinct from "nothingness"? (and the Vacuum)

« on: 20/06/2019 14:00:15 »

Is it possible to say that the expanding/evolving universe creates "space"  as a function of itself but that it expands "into" nothingness?

Also (separately but because these two thoughts occurred to me around the same time) is it possible for two objects to assimilate and become one object (I understand "objects" may be embedded in and part of  the various fields)?

16

Physics, Astronomy & Cosmology / Does the Universe expand into itself?

« on: 12/06/2019 00:48:30 »

I appreciate that there is no theory that explains anything before T^-43 secs into the supposed "beginning" of the Universe  but perhaps I can make the possibly unwarranted assumption that it "started" practically infinitely small,broke into 2 asymmetric  parts  and somehow continued interacting with itself and (from our vantage point) got larger and larger.

So ,with that (possibly very wrongly) assumed can I ask whether  it is fairly well understood that this Universe was not expanding "into" anything  but it was just simply expanding "into or out of itself"?

If that is the understanding ,might that imply that (and I know GR does not apply pre T^-43secs)  spacetime curvature was practically infinite in the "beginning" and has flattened progressively ever since (being completely flat now as far as we can tell except in local regions)?

A  kind of add on question I have is whether there could be any regions of the Universe where spacetime curvature could be negative.....?

17

Physics, Astronomy & Cosmology / What if the Earth was twice as massive?

« on: 08/06/2019 00:46:35 »

....but the same volume.....

I am wondering how many light minutes we would be from the Sun.

It is 8 light minutes now,isn't it?

Would this distance (Is it the same as the spacetime interval btw?) change (decrease?) as a result of the Earth's increased mass  ? Or would it only change when a new orbit was attained?

18

Physics, Astronomy & Cosmology / Is there a speed of propagation of energy?

« on: 06/06/2019 02:44:55 »

I appreciate that the speed of a massless object in a vacuum is invariant (c) but ,with em radiation the frequency  does depend on the frame of reference.

If one approaches the source the intensity of the radiation increases.

Can one say that the energy used to create the radiation at source is transmitted more quickly to the observer in this frame of reference than it  would be to an observer in a frame of reference  that was moving away from the source?

Can we talk about a speed of transmission of energy  ( units being expressed as energy x distance per second perhaps)?

19

Physics, Astronomy & Cosmology / What causes relative motion?

« on: 02/06/2019 17:34:50 »

Does "relative motion" only apply to classical objects or does the concept apply also in quantum mechanics?

Suppose we have a classical object (or an aggregation of  "quantum objects"-I understand they are modelled as excitations in a field) does anything  external have to happen  to cause these constituent parts to move in relation to each other  or is their initial configuration  enough to set this process in motion ?(no pun intended)

If no external intervention is required is there a correlation between the energetic content of the initial configuration and the resulting relative speeds of the constituent parts?

20

Physics, Astronomy & Cosmology / Is spacetime always understood in relation to the speed of light (em radiation)?

« on: 18/05/2019 13:06:11 »

I have been told (forget the context) not to get fixated on light in relativity ,that It is more fundamental than that.

My question is whether we can show the union between space and time in other ways (physically ,perhaps rather than mathematically but that would be good too)

Do we have to go to the quantum realm to  find processes where em radiation  is not a consideration ?

Is spacetime an equally valid concept in quantum physics as it is in Classical physics?

Is it more or less assumed that the classical forces  are more or less branches of one same force?