Gravitational reference point for every object in the universe

[JoeSchmuckatelli]

Oh - and one of the problems people have when trying to picture the Big Bang is imagining it from the outside.  Like at some point an imaginary observer could have seen an infitesimally small, impossibly dense point of light that exploded outward creating the universe.  We then imagine all the 'stuff' flying out into space forming stars and galaxies etc. 

That is apparently a very wrong way to think of it. 

There was never a way to see it from the outside. 

(let that wrinkle your brain for a bit!) 

[kerbiloid]

And see, we even didn't go to the nearest star, and the theories looking solid just several years ago (on this forum, too) are coming apart at the seams.

P.S.
So, don't overload your mind too much. In less than a century the theories will be replaced with revamped, better ones. Several times.

[Codraroll]

16 hours ago, RealKerbal3x said:

@Ariggeldiggel I'm no expert on this, but I do have an analogy that may help:

Imagine space as a three-dimensional grid, with galaxies sitting in it. This grid is constantly expanding in every direction, but the galaxies aren't physically moving away from each other - they're simply sitting in space and being carried along for the ride as every point on the grid becomes further and further from every other point.

Now, this doesn't prevent the galaxies from moving about in space normally, as we do see some galaxies such as Andromeda moving towards us due to gravity. However, it does provide an explanation for why everything in the Universe seems to be running away from us no matter where we look - objects aren't necessarily physically moving, they're just becoming further apart as space itself becomes physically bigger.

The interesting upshot of this is that the fabric of space doesn't need to obey the 'cosmic speed limit' aka the speed of light, because it's not made from matter or energy. This is why the observable universe appears to be about 93 billion light years across, despite being only 13 billion years old.

Hope this helped!

 

2 hours ago, KSK said:

This is not my analogy but I quite like it.

Imagine a balloon. Paint a bunch of dots on it to represent stars (or galaxies - whatever). Now inflate the balloon.

The radius of the balloon represents the time axis. The surface of the balloon represents 3D space. As we move forward in time, all the stars move away from each other but they’re not moving away from any single point in space although they are moving away from a single point in time.

For a while, I've found the expansion of the universe easier to imagine in one dimension. Imagine, if you will, a telescopic antenna like the one found on portable radios:

(from Wikipedia)

 

Imagine you're standing somewhere in the middle, on a telescopic segment that's slowly being pulled out of its neighbouring segment. So are all the other segments, at the same speed. That means that any given points on the segment in front of you and the segment behind you are slowly moving away from you, but the segments next to them again are moving away from you even faster. The segments at the ends of the antenna are moving very fast relative to you, and for that matter, so are you relative to them. 

The universe is sort-of like that, only the individual segments are infinitesimal but infinitely many. And also the entire thing is in three dimensions, of course.

Edited May 24, 2022 by Codraroll

[Terwin]

5 hours ago, Gargamel said:

I might have the misunderstanding here, but by the way I read your interpretation, it completely eliminates the existence of something like Cherenkov radiation, which we know to be a real thing.   

Nothing can go faster than c (speed of light in a vacuum = 300 Mm/sec)

Cherenkov radiation is due to particles going faster than light in a medium(usually water which is 225 Mm/s).

So any particle that is shot though water at a speed higher than 225Mm/s will give off Cherenkov radiation.  No need to go faster than c for this.

 

[Terwin]

16 hours ago, LHACK4142 said:

This reminds me of a different thought I had; If speed is relative, why can't things go faster than light? If you and another object are moving at lightspeed relative to the earth in the same direction, you and that other object are stationary relative to each other. So, why can't you accelerate to lightspeed relative to that object?

For an observer, they can seem to be moving faster than 300,000km/s, but that is only because as you approach c, the amount of time it takes for your subjective seconds to pass gets longer and longer.

If you are going 290,000 m/s, each of your subjective seconds takes 3.9448 seconds for someone at your origin point, giving you a subjective speed of ~3.8c

If you are going 295,000 m/s, each of your subjective seconds takes 5.615 seconds for an observer at your origin point, giving you a subjective speed of ~5.5c

So you *feel* like you are going faster and faster as you approach c, but only because time is slowing down for you.

 

Of course trying to figure out how this works when your origin point is traveling close to c compared to a reference point then you accelerate to bring your velocity close to that of this reference point, is beyond my simplistic understanding.

[kerbiloid]

As we "know" that at the  "opposite" _{"very far"} side of the Universe "nothing can go faster than c",
and as we get this "known" in a less than a human lifespan time,
and as "to know" means "to get this determined" in thermodynamic sense, i.e. "to change the state of the statistic system which we consider as our 'knowledge' ",
and as we presume that the statistical system of our "knowledge" is purely material and is stored as electromagnetic bonds in our brain,
and as we are obviously situating at light gigayears from that "opposite" side of the Universe,
and as it is an obviously material implementation of another statistical system,
and as a signal from there can come here (according to the "nothing can go faster than c" assumption) not faster than light,
thus the "far" material statistical (thermodynamic) system has affected the "near" statistical (thermodynamic) system faster than light comes (immediately instead of billions of years).

Hence we have just several cases:

1) Either the original assumption that "nothing can go faster than c" is wrong in common case, and is just postulated by the relativity theory as a condition of this theory applicability, and a particular case of a wider physical theory.
(It's normal. Say, the Newtonian physics has its own applicability conditions, like v << c).

2) Either the "knowledge" is "immaterial" in colloquial sense, i.e. it exists beyond the physical structure of our brain.

3) Either "c" locally varies from region to region, and thus the empiric data are fuzzy.

4) Or the relativity theory applies checkers rules to chess game.

See: the checkers queen/dame runs exactly like a chess bishop/officer!

But there are also knights, rooks, and others figures not described by the checkers.

The photon is that queen/dame/bishop/officer.

Btw, what's a speed of a chess piece? Infinite?

Is it like the photon, in every point of its path at once.

[Bej Kerman]

8 hours ago, Gargamel said:

9 hours ago, Bej Kerman said:

I'm not sure who said speed is relative, because speed isn't relative; space and time are relative. Speed is relative to the fabric of spacetime - you can't move through spacetime faster than light regardless of anything else that happens to be laying around in spacetime. That's just my understanding, though.

I might have the misunderstanding here, but by the way I read your interpretation, it completely eliminates the existence of something like Cherenkov radiation, which we know to be a real thing.   

How so?

3 hours ago, Terwin said:

So any particle that is shot though water at a speed higher than 225Mm/s will give off Cherenkov radiation.  No need to go faster than c for this.

Oh, I see. Gargamel thought Ckv Radiation happens when something goes faster than c, which isn't right because relativity explicitly says nothing with positive mass goes faster than c. Although, this just confuses me further because it implies they thought I forbid travel faster than c in my comment even though FTL travel has been forbidden by relativity for as long as relativity has been a thing.

[Gargamel]

15 hours ago, Bej Kerman said:

I'm not sure who said speed is relative, because speed isn't relative; space and time are relative. Speed is relative to the fabric of spacetime - you can't move through spacetime faster than light regardless of anything else that happens to be laying around in spacetime. That's just my understanding, though.

 

5 hours ago, Bej Kerman said:

How so?

Oh, I see. Gargamel thought Ckv Radiation happens when something goes faster than c, which isn't right because relativity explicitly says nothing with positive mass goes faster than c. Although, this just confuses me further because it implies they thought I forbid travel faster than c in my comment even though FTL travel has been forbidden by relativity for as long as relativity has been a thing.

No, I don’t think Cherenkov radiation happens when something exceeds c.  You said speed of light, which is not necessarily c.
 

Please do not put words in my mouth.  

[sevenperforce]

Why doesn’t the forum notify me — ME — when a fascinating topic like this is broached?!?!

Here’s the best way I’ve come up with to visualize it all. First, assume the universe is infinitely large. It might not be, of course – in fact, there are reasons to think it is not – but just assume that it is for the purpose of this visualization. The universe is infinitely big and there is stuff everywhere in it, no matter where you go. Snap your fingers and teleport as far in any direction as you can imagine, then teleport 1 billion times farther, then 1 trillion times farther, and repeat that process 1 quintillion times every second until billions of years pass and the sun expands and swallows the earth, and you are still going to find yourself surrounded by the same kind of galaxies we see all around us. A truly infinite universe.

 Now, imagine that in a Thanosian display of cosmic might, you can snap your fingers once again and squeeze that entire infinite universe until every point in space between here and the Andromeda Galaxy is compressed into the span of a single meter. Have you made the universe any less wide? No, you have not, because you could still travel just as fast in any direction for just as long as you could imagine and you would still find yourself no closer to the edge of the universe than before. Granted, all of the universe you experience is now denser by a factor of about 3.2 billion trillion, but the universe still remains infinite so you’re still right in the “middle” as best as you can tell.

And even if you keep snapping your fingers over and over and you keep compressing the universe by a factor of 3.2 billion trillion every second, the universe still gets no less broad. But then you think of one last trick. You start snapping your finger faster and faster, until the rate at which the universe is being compressed approaches infinity. And then something different happens. Because when an infinite universe is compressed until it is infinitely dense . . . well, that’s something entirely new. It’s a special kind of singularity — something infinitely large and yet infinitely dense, something that is “everywhere at once” only by virtue of the fact that it literally consists of every “where” at once.

That’s the Big Bang. Not a “where” but just a “what”.

Edited May 25, 2022 by sevenperforce

[kerbiloid]

Imagine the Unverse like a large inflatable balloon.

Spoiler

 

(There were even more illustrative gifs with balloon rabbits illustrating both periodic and multiple Universes, but they were too much illustrative.
Perhaps, probably much closer to the real design of the World.)

Edited May 25, 2022 by kerbiloid

[Bej Kerman]

10 hours ago, Gargamel said:

You said speed of light, which is not necessarily c.

Speed of light is always c; speed of light in a medium is different.

10 hours ago, Gargamel said:

Please do not put words in my mouth.  

Apologies if it came off that way. Trust me, that is not what I meant to do.

[farmerben]

It may be possible to define absolute rest and absolute motion.  If the amount of redshifted and blueshifted objects in every direction are equal you are essentially at rest.  If you began moving closer to the speed of light the appearance of the entire universe would change.

 

That the speed of light is constant in every direction is neither an observation nor a hypothesis.  It is an axiom we can stipulate in order to create a definition of simultaneity.

 

[benzman]

I could listen to Carl Sagan's voice all day.

[Terwin]

2 hours ago, farmerben said:

It may be possible to define absolute rest and absolute motion.  If the amount of redshifted and blueshifted objects in every direction are equal you are essentially at rest.  If you began moving closer to the speed of light the appearance of the entire universe would change.

You propose a definition of absolute rest to be going at a speed that is the average of your observable universe?

Wouldn't that mean (possibly rapid) acceleration every time something left your observable universe?

I think I would have difficulty agreeing that a state is 'absolute rest' if I can be pulled out of that state due solely to a very distant object moving beyond my detection range.

 

 

[farmerben]

12 minutes ago, Terwin said:

You propose a definition of absolute rest to be going at a speed that is the average of your observable universe?

Wouldn't that mean (possibly rapid) acceleration every time something left your observable universe?

I think I would have difficulty agreeing that a state is 'absolute rest' if I can be pulled out of that state due solely to a very distant object moving beyond my detection range.

 

 

If the universe appeared blue in one direction and red in other directions, then we would know we not at rest.  We might be in an inertial reference frame which we could claim to be rest, and the universe moving in a peculiar asymmetric way.   If we see symmetry then we are in some sense at rest relative to some absolute standard.

[Terwin]

29 minutes ago, farmerben said:

If the universe appeared blue in one direction and red in other directions, then we would know we not at rest.  We might be in an inertial reference frame which we could claim to be rest, and the universe moving in a peculiar asymmetric way.   If we see symmetry then we are in some sense at rest relative to some absolute standard.

Due to expansion, this would allow multiple objects that are at 'absolute rest' even though they are traveling at close to C relative to each other if they are far enough apart.

[cubinator]

The average velocity of galaxies within a certain region is often used as a reference for a resting frame, however since there is no guarantee that that group couldn't be moving at great speed relative to some other group then it isn't a universal absolute reference...even if that region measured is the whole observable universe.

[farmerben]

2 hours ago, Terwin said:

Due to expansion, this would allow multiple objects that are at 'absolute rest' even though they are traveling at close to C relative to each other if they are far enough apart.

Agreed.

It's not easy to pin down an exact standard of absolute rest.  The relativistic distortions only show up when moving close to the speed of light.

[kerbiloid]

Happily, the gas molecules don't have absolute speed.

[Bej Kerman]

6 hours ago, kerbiloid said:

Happily, the gas molecules don't have absolute speed.

What?

13 hours ago, farmerben said:

If the universe appeared blue in one direction and red in other directions, then we would know we not at rest.  We might be in an inertial reference frame which we could claim to be rest, and the universe moving in a peculiar asymmetric way.   If we see symmetry then we are in some sense at rest relative to some absolute standard.

Nothing is at rest, though.

[kerbiloid]

56 minutes ago, Bej Kerman said:

7 hours ago, kerbiloid said:

Happily, the gas molecules don't have absolute speed.

What?

Relative to the center of the Universe.

[Terwin]

3 hours ago, Bej Kerman said:

What?

General relativity says that there is no absolute frame of reference.  Everything is only relative to a specific point of observation.

 

I had a physics professor that claimed he would define his house as the center of the universe.  It may make some of the math more complicated, but it all works out.  It is also just as technically valid as any other possible 'center-point'.

That is also how you define an immovable object: that object is your reference point, so no matter if it is closer to Earth or Jupiter, it is still your origin point, and thus, by definition it has not moved.(but the math on the rest of the universe may get a bit complicated if a force is being applied to your immovable object...)

[wumpus]

21 hours ago, farmerben said:

It may be possible to define absolute rest and absolute motion.  If the amount of redshifted and blueshifted objects in every direction are equal you are essentially at rest.  If you began moving closer to the speed of light the appearance of the entire universe would change.

That the speed of light is constant in every direction is neither an observation nor a hypothesis.  It is an axiom we can stipulate in order to create a definition of simultaneity.

First, you won't ever see an equal amount of redshifted and blueshifted in an expanding universe (like ours), nearly all mass will be redshifted.   Second, that the speed of light is constant in every direction was observed by Michelson and Morley in 1887 and confirmed ever since (with recent slight modifications for gravity waves).  Einstein might have made it an axiom for relativity, but no matter how many times relativity is tested it somehow measurement matches its predictions.

[kerbiloid]

To bring a little scare to the discussion.

Spoiler