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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         

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Just Chat! / Re: Do you think sports is science?

« on: 26/06/2019 11:12:02 »

Seems to involve psychology. You cannot listen to a commentary for 5 minutes without a commentator telling us what a particular participant "must" be thinking - or the team "they mustn't sit back on their lead" .

The manager is some kind of high priest in the process "what did he tell them at half time?".

Some of us hated sport (even whilst enjoying playing it). Perhaps it shows? 

(Used to skive off for a trip into town half way through the cross country runs .)


edit What this thread is doing in "Physics, Astronomy & Cosmology"  have no idea.

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

« on: 21/06/2019 13:04:39 »

Is "Space" distinct from "nothingness"? (and the Vacuum)

My attempt:
A vacuum is when you have removed all the baryonic matter from a volume of space.
- You have to work very hard to ge a "good" vacuum, as atoms are always boiling off the container walls and seals.

If you really want nothing, you would need to remove light (not entirely possible above absolute zero), neutrinos (not possible with any shielding we can imagine), and Dark Matter (we don't even know what it is, let alone imagine a way to keep it out).

OK so are we better just (re)starting from the position that a vacuum is not only impractical to create but that it is a misnomer  and that we can only really talk about relative densities of whatever we are considering?

My first introduction to this idea of a vacuum was the "Nature abhors a vacuum"  saying which made such perfect sense to me at the time.(with its seeming relevance  to both physical and political events)

Time to cast "vacuums" into the bin of history?

"Nothingness" is clearly also a contentious subject (I think Odysseus  got the better of one of his opponents with his "My name is  Nobody "   repartee).

I don't think we need to pick at that scab for now ;-)

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

« on: 21/06/2019 00:41:54 »

Could you give me an example?

Well some have said that a Field is a set of measurements but others have said "no a Field is a thing in its own right".
From my lowly position in this "field" of knowledge ,I am not in a position to adjudicate.

However , in my question which you have addressed I accept I was treating Fields as objects in their own right.

So ,to give you the example I had(based on that possibly flawed understanding) it would go like this;

Suppose we have a charge in one location then it will have its own Electric Field .
Now ,if we have another separate  charge  it will also have its own Electric Field.
These two electric Fields will (per my understanding) interact with each other  and it will be  (again as I anticipate) possible to view the two separate Fields as one "conglomerate"

Any particles associated with this "combination Field" can (again in my possibly very flawed understanding) be attributed to either Field of both (actually,I would guess to both.)

Extrapolate to all the Electric Fields in the Universe and we have one Electric Field (to rule over all ;-)  )

I took the Electric Field as an example. I assume the same might apply to any of the other kinds of Fields there are ...

Now that is what I had in mind (you did ask)

I hope not to be too embarrassed by your reply

Oh and thanks for looking at the other thread I mentioned.

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

« on: 20/06/2019 14:59:41 »

That all depends on one's definition of 'object'.  The word seems to be an abstract one with no physical meaning.  It simply means this collection of <whatever> being considered/treated as a unit

Probably how I was using it ..It seems like a "one size fits all" description. A Field might also be an object , I suppose(and everything is part of the Field(s) isn't it?

So Fields do merge don't they and particles might be "one object" if they are all excitations of the one (combination of) Fields

.Hope I am not talking gibbonish ;-)

btw My last (unanswered thread) was "Does the Universe expand into itself?"

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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)?

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Physics, Astronomy & Cosmology / Re: Do Matter Waves collapse when bumping into any large object?

« on: 17/06/2019 10:44:54 »

Is it possible to say as an approximation how the  complexity of the mathematics of quantum mechanics  compares with that of GR?

I have heard that GR is number crunched to produce prediction and is extremely lengthy. Does the same apply to QM?

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New Theories / Re: How will buckyballs fired at a double slit behave?

« on: 16/06/2019 12:10:11 »

Anyone who remembers "The Fly" will recall the problems of reassembling atoms in their original order. Indeed the fact that a double slit transfer redistributes stuff into a transform of the slit convoluted with the incident beam, suggests that the probability of recombination in a recpognisable order is even less than Eddington implied. But that classic film ignored the fundamental conservation of matter - the fly could not be more massive than the original, nor could Bart Simpson, in the famous spoof remake, get any smaller.   So no long finger, unless some orther bit is sacrificed..

Perhaps just musing ,but is there a definition of "order" in the way you have just used it that applies to quantum mechanics in a way that is different (or the same as) to the way it is used in classical mechanics?

I imagine there might be spatial order and temporal order -or is there a fusion between the two?

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New Theories / Re: How will buckyballs fired at a double slit behave?

« on: 16/06/2019 10:36:26 »

Eddington pointed out about 100 years ago that if a student of physics fell through an intact floor and rematerialised in the room below, he would not consider it a miracle but merely one of the less probable solutions to a multivariable equation.

Alas, this obvious and profound observation seems not to have reached the elementary school syllabus yet, though it is plain that the regular contributors here understand it.  What baffles me is why those who don't, frequently accuse us of sharing their delusions.

Is there a (exponentially remote) chance that the  student rematerializes slightly lacking in physical integrity  ?

Say ,for example with a finger slightly longer?

Are there some scenarios that might be impossible no matter how remotely possible?

Edit : is it a reasonable observation that any body, alive or inanimate , goes through spacetime "shedding" countless parts of itself from one moment to the next as  "quantum components"  disappear  for their own quantum reasons leaving the persisting macro body to sail on in its new overall state regardless of what is happening to that body at the macro level?

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New Theories / Re: How will buckyballs fired at a double slit behave?

« on: 15/06/2019 09:50:17 »

Can you even give an example of something that exists that doesn't have mass/energy? Even space-time contains mass/energy in the form of vacuum fluctuations.

Is that just because (or connected to the fact that) any measurement of mass/energy  is relative to a reference frame and all reference frames' location  are uncertain in the real world?

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Physics, Astronomy & Cosmology / Re: How do you introduce new food flavours?

« on: 12/06/2019 15:34:00 »

Ironic that there should be spam in a link about healthy eating...

Hope we are not being corny here.

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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.....?

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

« on: 09/06/2019 15:18:09 »

I said it would move to a lower orbit because it would be colliding with all that mass, which might slow it down and cause it to fall.

As a nonsense thought experiment, (nonsense because the premise breaks all conservation laws), you're saying that suddenly there is this 2xEarth where Earth was, moving for the moment in the same trajectory.  For the most part, this is equivalent to dropping a large and small rock from the tower of Pisa.  They still fall at the same rate since on the grand scheme of things, they're both pebbles, as the Earth is a pebble in relation to the sun.

If you put something actually big where Earth is (like another star rivaling the sun), then the orbit would change as the object is large enough to significantly pull the sun away from where it would otherwise be.  The orbital radius would drop.  Likewise, if I dropped a moon mass from the Pisa tower, it would get to the ground in a bit less time than would the rocks, not because its acceleration is higher, but because the moon is massive enough to pull the Earth up to meet it partway.

Thanks.  So ,if an object moving in space was to eject some of its more massive components  in a symmetrical (and instantaneous)  way so as not to disturb its direction of travel it would not speed up as a consequence  ?

I had (wrongly) understood that to be the case  from what you said at the end of your first reply to the OP.

("More likely, the meteors will come from all directions and add pretty much no net momentum to Earth, in which case it will drop to a lower orbit since a larger mass with the same momentum will move slower, and slowing makes an orbital thing drop to a lower orbit")

Your clarification  seems to show that I misunderstood that scenario.

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

« on: 09/06/2019 10:03:30 »

More likely, the meteors will come from all directions and add pretty much no net momentum to Earth, in which case it will drop to a lower orbit since a larger mass with the same momentum will move slower, and slowing makes an orbital thing drop to a lower orbit.

Would that be a good science fiction  idea (to go along with warp drive etc)?

The "Mass Attenuator" would provide the means for accelerating massive objects up to light speed,wherupon the Uncertainty Shift would  move the craft into Tachyonic Overdrive. (Warp Drive would be for directional control perhaps)

Actually ,when I said the Earth could double in mass I meant instantly as a thought experiment.

You say it would move to a lower orbit . So the increase in spacetime curvature  would not counteract that to any degree?
 

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

« on: 08/06/2019 23:53:50 »

The important diagram is the one below (1.2) which shows why, in 2D, the distance s (or Δs) doesn’t change with a change of coordinates. You really don’t need to go beyond (1.3) which is the spacetime interval and is really only 1.2 in 4D

OK ,well I got that ,then .Yes that was interesting and perhaps a bit of an eye opener for me to see   those  2d rotations ( change of coordinate systems) which seem similar to those boosts in Minkowski diagrams.

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

« on: 08/06/2019 13:35:48 »

8 light minutes is a distance (a space interval) ie the distance light would travel in 8mins.
8mins is a time interval.
Spacetime interval is different and is special because all observers agree what it should be. It is related to Pythagoras’s theorem and can be used to calculate a distance in different coordinates and get the same answer. This link shows how it works https://ned.ipac.caltech.edu/level5/March01/Carroll3/Carroll1.html far better than I can try to explain here.
Remember, a major part of relativity is about how we view things from different coordinates.

That is heavy going(I am getting confused about the double subscripts in (1.8 ) and can't really carry on further   with that fly in the ointment (I have come across that usage before but it is nothing like second nature and I can't see what Caroll's  "μ" refers to -seems a bit like it came out of the blue)

Just on that 8 light.minutes , what might be a figure  or formula for the emission of a photon  and its reception on the Earth that might  be expressed as a spacetime interval?

What would ,for example a rocket progressing along the Sun-Earth axis measure "our" 8 light.minutes as and how would they calculate it (I had assumed everyone might agree on that number but now I am starting to expect/suspect that they will not.

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

« on: 08/06/2019 01:34:01 »

The 8 light minutes is not a spacetime interval?

Are you sure?

Is it  not a measure of the interval between the emission of the light from the Sun and it's  detection on the Earth?

I was actually wondering what would happen to that 8 light minute interval (whether it is a spacetime interval or just spacial) if the mass was doubled instantly (magically perhaps as a thought experiment)

What would the new distance be ?

Would it be stable ? Would it increase or decrease (I think you said it would increase as Earth would drop to a lower orbit)

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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?

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

« on: 06/06/2019 12:24:33 »

Energy times speed isn't a transmission rate.  Speed of transmission would be energy per second, which is known as 'power'.  Are you talking about something other than frame dependent power?

I think you are right (I was very unclear/muddled  about that).

Suppose we have a "power sensor" moving away from a power source at a relative speed approaching c...

Would it reading not drop to  zero  (as a limit and not simply as a function of increasing distance-as a result of the Doppler effect)?

Is there a "propagation of energy" in that scenario which is also dropping towards zero?

And conversely if  the sensor approaches the source  at a relative speed approaching c ,does this "speed of propagation of energy" approach  infinity?(Does it increase with both decreasing distance AND  increasing speed  or is it just the former as you said in your reply?)

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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)?