Spacetime is the medium!

Aug 31, 2021
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I often contemplate about Universe. My newest insights are as follow:

Spacetime must be medium because it supports stuff. Nothing is falling nowhere and it probably has internal structure, armature of sort, in the form of underlying quantum field. But it is also a special medium which does not interact with light. Matter can reflect, refract or absorb photons. None of that is happening in the intergalactic vacuum and the temperature is near absolute zero. Why matter interacts with light? Because of the electron and photon synchronicity: if there is no frequency correspondence the photon will reflect in the case of a non-black body or be absorbed in the case of the black body. If there is partial correspondence photon will pass through the matter and refract. Actually, I am not sure does original photon passes or its energy is carried across among adjacent electrons, carried I believe. Light refracts because of electron orbit change due to the energy excitation. Intergalactic vacuum does not interact with light but supports stuff like a cushion.

Now think about dark matter briefly: it has gravity but it can not be seen. Maybe there is no electrons. Just protons and neutrons without electrons. Or some special state of electron or like-electron.

Dark matter is intermediate.

What can comprise intergalactic vacuum since there is no gravity meaning no matter no dark matter? Only 1 particle in 1 cubic meter and the rest is zero-point energy. Maybe powdered quarks mixed in the solution? I doubt. Nothing. There is nothing except underlying quantum field acting as an armature together with allocating mass. Hence the photons travel undisturbed for billions of years through the Universe and we can observe the cosmic past with our telescopes.
 
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Jan 4, 2022
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spacetime is the is like a viscous liquid with low viscosity ,as you said the spacetime is medium for start and stop of any events in the universe and switchinfg into different field universe or multiverse too .interaction is only when the absolute temperature is reached .untill then its non-interactive or we say inert medium.its time that drags space in time . hence things go forward and spacetime is flexible or elasticity is in entropy. we observe spacetime squeezing the celestial bodies to keep them in space along with expansion of the bodies flying apart.
 
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Catastrophe

"There never was a good war, or a bad peace."
"spacetime is the is like a viscous liquid with low viscosity"

Two participants here seem to be suggesting that spacetime has properties.
That is the crux of my question.

I am pleased to see the interest, but I would like to ask how many people, in their heart of hearts, still believe that spacetime has sufficient substance, in its own right, to expand and drag massive objects (stars, galaxies et cetera) along with it?

I have no firm opinion on this. I can see all the evidence. I can see some of the 'fudge factors' but I can also see some of the areas of reservations.

Is spacetime real, or just a useful imaginary crutch?

Cat :)
 
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Is spacetime real, or just a useful imaginary crutch?
Yeah, it's a weird duck, admittedly.

Before Einstein was willing to put GR on the table, he knew he needed multiple lines of objective evidence to get people to realize nothing but his equations could match what is, or isn't, observed. It was going to be a hard sell for many other scientists.

For years, astronomers searched for the illusive planet Vulcan that had to be orbiting near the Sun -- so it was very hard to see in the glare -- but was the only possible explanation for the odd orbital behavior of Mercury.

When Einstein first applied his equations to the Mercury orbit problem, he nailed it. Vulcan vanished. [He said he had heart palpitations for days due to the excitement.]

But he wanted two more solutions to the problems others could not resolve.

Solar astronomers had shown that the wavelength of sunlight was a little too red to make sense. GR solved this nicely.

The final test was in trying to get astronomers to measure the bending of light around a star that was positioned very close to the Sun during an eclipse. Given the angular distance from the Sun, its light must bend a certain amount. Eddington's solar images during the 1919 eclipse demonstrated that the angular difference was about 2x that of Newton's equations, which happen to match Einstein's equations. It was this event that made Einstein a household name.

GR has been tried and tested in so many ways and has been accurate to the deepest degree possible so that it falls into the category an equipment salesman once used to describe the used roller he was selling me, "It's jam-up, jelly tight, armor plated and bullet proof!" :)
 
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Catastrophe

"There never was a good war, or a bad peace."
Helio, I am very much aware of the strength of GR.

What worries me is comments like this:

"spacetime is the is like a viscous liquid with low viscosity" [sic]

There seems to be an undercurrent of aether - hence my question.

I was not suggesting that it was the first choice of cutting edge cosmologists.

I don't know the answer. Admittedly, it is counter intuitive that 'imaginary' depressions in a solely mathematical framework can 'drag around' not inconsiderable masses like galaxies - so I can see the problem.

And no answers seem to be forthcoming about the Michaelson-Morley experiment, or the potential 'drag' of light in viscous media, let alone groups of galaxies.

Cat :
 
I’m more and more respectful of spacetime, so it’s becoming less and less imaginary. It’s physical enough to force light to propagate at only one speed, and it directs effortlessly the path for all orbits. Yet its motion is truly enigmatic due to time’s influence, apparently.
 
Jan 4, 2022
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in the spacetime continuum , space and time has to be parallel and not interlaced or perpendicular . as to . create a gravity tense . we need the two entities as parallel . its not that reperesentation of a tray ( your GRID) . waving in with masses in and...out?possibily the thought of grid in tray and wave formation of gravity representation must change ..As we see gravity is not generated by a mass body ,but when a mass body is squezed in to the space-time space-time generates a gravity in force to crunch the mass body and stabilize it into the orbit or path .
 

Catastrophe

"There never was a good war, or a bad peace."
Helio,
"so it’s becoming less and less imaginary"
I am tending to agree with you.
But the whole idea is haunted by Michelson-Morley.
For me, the whole subject i "work in progress".

Cat :)
 
Helio,
"so it’s becoming less and less imaginary"
I am tending to agree with you.
But the whole idea is haunted by Michelson-Morley.
For me, the whole subject i "work in progress".
The Michelson-Morley result set-up SR for Einstein because c became invariant, serving as the only explanation.

Time dilation becomes simple math once c is fixed for all reference frames.

Gravity took Einstein 10 years to integrate. I read today (a. zee) that the solution for GR involves 10 equations. For the simple linear example, 3 of them = 1; 4 of them = 0; 3 of them = -1. Not “back of the napkin” stuff. :)

iphone
 

Catastrophe

"There never was a good war, or a bad peace."
Helio,
But the whole idea is haunted by Michelson-Morley.
Maybe not the best phraseology on my part.
What I meant was that, more and more, there seems to be (on the part of some people) the need to fill spacetime with something (as aether with M&M) from a viscous fluid to other variants on aether.

Cat :)
 
Ok. Yeah, the M&M experiment revealed that light is completely independent of the aether. Some argue that this proved that there is no aether, which is not correct. Given the strong support for virtual particles popping in and out, and that 95% of the mass/energy of the universe is stuff we can't see, perhaps aether is not a bad word for it.

The question not asked is what flow does it have? The only flow seems to be that of the Hubble Flow (i.e. expansion), which is tiny locally. But even this has no impact on light's super-fixed speed.
 

Catastrophe

"There never was a good war, or a bad peace."
Helio,
perhaps aether is not a bad word for it.
That is very interesting. Does this mean that there is something for light in? Please forgive my lack of understanding in this area. I am unsure as to whether or not light needs some medium to vibrate in?

Cat :)
 
That is very interesting. Does this mean that there is something for light in? Please forgive my lack of understanding in this area. I am unsure as to whether or not light needs some medium to vibrate in?
That's a good question!

I think it is like you and I being within the Earth's magnetic field, but essentially unaffected by it. Light goes from point A to point B, which are in space, but light is not influenced by space itself, at least not in the conventional sense.

However, I read from our author, a. zee, that light travels from A to B not by taking the shortest distance but by taking the shortest time. I found that interesting. He used the analogy of a lifeguard (Feynmann for some reason. :)) who must save a drowning woman by running down the pier and jumping in to save her. If he simply jumps in from the beach, the slower swimming speed, vs. running, will not be the fastest route. If he runs all the way down the pier to be perpendicular to her, then this too won't be the fastest. The fastest will be to jump somewhere along the pier that produces the fastest time for both legs (running and swimming). This happens to match how light bends in, say, water (i.e. refraction). I'm not sure if this is the best model (fastest time) for light since I've seen wavefronts produce the same result, but it is definitely intriguing.

[He never included the pier but simply used the beach, which is impossible so his simplicity fails, IMO.]
 

Catastrophe

"There never was a good war, or a bad peace."
I am not too sure I understand the analogy. If you include the pier, then the quickest time must be very close to the perpendicular. is it not a compromise between the time saved in jumping, being faster than running, assuming that the time in the air is directly towards the woman, and the slightly further distance swimming? So the shortest time would be jumping very close indeed to the perpendicular. Or have I got it all wrong? :(

Cat :)
 
I am not too sure I understand the analogy. If you include the pier, then the quickest time must be very close to the perpendicular. is it not a compromise between the time saved in jumping, being faster than running, assuming that the time in the air is directly towards the woman, and the slightly further distance swimming? So the shortest time would be jumping very close indeed to the perpendicular. Or have I got it all wrong? :(
Yes. I played with it, without having to use WD40 to release my prior knowledge of calculus, and found the following:

Swimmer distance = 82 meters: 80 meters down the pier, 18 meters out from the pier.
Speed running = 8 mps; speed swimming = 2 mps.
Optimal time to flailing swimmer on surface happens when jumping in the water at 75 meters down the pier, which, by coincidence, is an angle of 75 degrees. :)
 

Catastrophe

"There never was a good war, or a bad peace."
Helio,
Answer: tan 75° + cot 75° = 4.
Is this relevant? I am looking for any other "simple solutions".
OK, "Optimal time " is ?
Sorry, the plaster on my kitchen ceiling has just come down (about midnight here) and my maths head is not working. This is true. I am not kidding. Just finished clearing up.

Cat :)
 
Helio,

Is this relevant? I am looking for any other "simple solutions".
I picked a random example just to see if it would be easy to solve. Calculus would have been my first choice...40 years ago. :). [ set derivative = 0 for min. time.]

That 75 deg. trig trick is cool. :)

The saving time was easy to solve with Excel using iterations. Other distances will produce different optimal angles. [OOPS. See posts 20 and 21. Only one angle seems to work.]

Sorry, the plaster on my kitchen ceiling has just come down (about midnight here) and my maths head is not working. This is true. I am not kidding. Just finished clearing up.
Ug. Do you know the cause? Moisture?
 
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Helio, did I get it right in post #15?

If so, we need the speed and distance? Have I got the model wrong?
I just checked your 75 deg. angle as an optimal jump-off angle for any distance the struggling swimmer is from the pier and, much to my surprise, you are correct!!

The optimal angle is always 75.51 deg. I'm a little doubtful of my math to produce such a non-intuitive result. I would think closer to the pier would bump it closer to the 90 deg. angle, but the swim time becomes negligible even at the 75 deg. jump-off.

Did you know it would be ~ 75 deg?
 

Catastrophe

"There never was a good war, or a bad peace."
Helio,
Did you know it would be ~ 75 deg?
If you remember, my thought process was:
If you include the pier, then the quickest time must be very close to the perpendicular. is it not a compromise between the time saved in jumping, being faster than running, assuming that the time in the air is directly towards the woman, and the slightly further distance swimming?
I could not do a precise calculation without knowing the speed and distance of the jump. I see that the distance, your d2, would increase in importance as you approach 90 deg i.e., the proportion of the jump of d2 (at high speed, and towards the swimmer would increase in importance) Thus, I would stand by my initial suggestion that the full 90 might be the optimum. If the jump were equal to K, taking virtually 0 time, this would be quickest. I suspect this was not the answer anticipated by the questioner, but lateral thinking is important.

If K >> distance jumped, I think the answer is still the same, but I could be wrong ;) There may be a (high) value of K, where the jump distance is insignificant, where it changes i.e., if jump is "infinitely" small proportion of K, then the problem reverts to the maths where jump = 0.


Cat :)

P.S. The height of the pier would also be important, as it would affect the distance of the jump. ;)
 
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I will double check the math this weekend, when I may, or may not, have time.

I think the answer is correct.

The angle is greatly affected by the relative difference in speeds.

So changing the swimming speed to a phenomenal 9 mps yields a 26 deg. angle. But for only a 1 mps swim speed, the angle gets closer to the 90 deg. point (84 deg.).

The point of the analogy is to use it for understanding light. We know Snell's law (some say it should be Snel), but if we know the two speeds for light in air and glass (or water) we can calculate that angle and compare it the refraction index. So the simplification of the pier info, etc., was necessary to hold the analogy.

What is interesting, and now logical, that changing the distance to the swimmer should not affect the jump off angle else it would prove fatal to the analogy. So this is an interesting story, IMO.
 

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