How does Gravity exist?

[Green Baron]

Sleep well, i don't want to get into arguing and i don't need the last word, so i am out ;-)

Edit: Did that sound disrepectful ? It is not meant so !

Edited September 12, 2017 by Green Baron

[Mr. Quark]

Just now, Green Baron said:

Sleep well, i don't want to get into arguing and i don't need the last word, so i am out ;-)

If you be respectful etc I'd call it debating.

[Steel]

41 minutes ago, kerbiloid said:

All three other forces unite into one ((electomagnetic + weak) + strong) and can be treated as three manifestations of one fundamental force on different scales.
So, unlikely it is correct to say that weak and strong have finite range. They are measurable manifestations of the triple force on short range.
And one of main physical problems currently is "how to unite gravity and electro-weak-strong force in one."

That's a little bit of a misunderstanding. It is true that electroweak theory is well established, however, this unification only occurs at insanely high energies like those found in the immediate aftermath of the Big Bang. In the universe today the four forces are distinct. Moreover, a theory unifying the strong force, or a Grand Unified Theory, is still a long way off, and there is no significant evidence that the universe is in fact described by a GUT. Unifying gravity is way beyond us at this point in time.

Thus, the forces act as distinctively in our universe in its current state, with the weak and strong forces having very short range.

 

41 minutes ago, kerbiloid said:

It moves galaxies and keeps them together.
That's the human's rulers are short, not the gravity is weak.

That's not really true, on any scale where you can compare forces (i.e any scale where the strong and weak forces still exist, i.e. over the scale of a proton), gravity is by far the weakest force. Also, if you dive into various field theories, gravitational interactions are quantifiably weaker than the others. Just because gravity has a longer range does not mean it is stronger, just that it reaches further. It is a bit like having a very long piece of string and a very short piece of rope, just because the string is longer does not mean that is is stronger.

Edited September 12, 2017 by Steel

[kerbiloid]

7 hours ago, Steel said:

It is true that electroweak theory is well established, however, this unification only occurs at insanely high energies

Yes, it's presumed to appear at 10¹⁴ GeV energies. But this doesn't matter.
"Big", "small" are just human subjective description of different scales, uncommon for daily activities.
They become the same force in the same Universe - only that matters.

7 hours ago, Steel said:

That's not really true, on any scale where you can compare forces (i.e any scale where the strong and weak forces still exist, i.e. over the scale of a proton), gravity is by far the weakest force.

Measuring galaxy movement, there are now Weak and Strong at all. Only Gravity and smetimes, but locally - Electromagnetism.
Subjective "weakness" and "strongness" depends only on scale.
Electromagnetism has the widest range of scales where it stays observable. But, say, in Universal scale it is much less significant than gravity.
At star-size scale both are more or less equal.
At atomic and subatomic level effects of gravity  are too slow to be observable.

7 hours ago, Steel said:

gravitational interactions are quantifiably weaker than the others

How much is Weak or Strong interaction value between the galaxies?
Negligible compared to the Gravity and even to Electromagnetism.
There are no "weaker" and "stronger", there are "faster" and "slower" at that scale of distances, or "shorter" and "longer" at that scale of durations.
Looking at the Universe from bird's eye view, there is nothing except Gravity at all. Maybe, some Electromagnetism.

("Force" is another one derivative value, it doesn't have a conservation law.
Hamiltonian mechanics knows no such thing.
They call "force" a time derivative from momentum or distance derivative from energy.
They call "mass" an empirical coefficient in these two derivatives.)

8 hours ago, Green Baron said:

Sleep well, i don't want to get into arguing and i don't need the last word, so i am out ;-)

Edit: Did that sound disrepectful ? It is not meant so !

Thanks.
The book at the link is the very beginning of theoretical physics course for a classic university .
Hamiltonian mechanics is the very first chapter of this very first volume.
(Orbital movement equations appear in this chapter like a bonus).

It can introduce you into the basics, and it doesn't use any "mass" at all, only "energy", "momentum" and "coordinates", pure mathematics.

And Equivalence principle is still actual, whether you like wiki, or not.

Edited September 13, 2017 by kerbiloid

[Green Baron]

3 hours ago, kerbiloid said:

Thanks.

The book at the link is the very beginning of theoretical physics course for a classic university .
Hamiltonian mechanics is the very first chapter of this very first volume.
(Orbital movement equations appear in this chapter like a bonus).

It can introduce you into the basics, and it doesn't use any "mass" at all, only "energy", "momentum" and "coordinates", pure mathematics.

And Equivalence principle is still actual, whether you like wiki, or not.

He, don't get too bold !

[qeveren]

23 hours ago, kerbiloid said:

How much is Weak or Strong interaction value between the galaxies?

Negligible compared to the Gravity and even to Electromagnetism.

Gravity is influential at long distances because it isn't self-neutralizing like the other three.  It still empirically possesses the smallest coupling constant and is thus the weakest interaction.  When people talk about the strength of a fundamental force they're talking about its coupling constant, not its influence on the large-scale structure of the universe.

Edited September 14, 2017 by qeveren

[p1t1o]

I went to a lecture once at the Royal Academy by some eminent physiscist or other, and if I remember it correctly, it talked about (under certain theories or hypotheses) how gravity is so "weak" because it is capable of "leaking" into other universes or "branes". Its strength is effectively diluted between multiple layers.

Hence, dark matter is us detecting the gravity of masses in other universes.

And further, this could be harnessed to communicate between universes in a real way.

 

There you go, discuss!

Edited September 13, 2017 by p1t1o

[mikegarrison]

Gravity pulls us toward the center of the Earth. What (obviously stronger) force keeps us from falling there? What creates the resistance that keeps one solid object from moving through another? The standard answer seems to be "the Pauli Exclusion Principle", but if everything comes down to four forces, which one is involved in that? Is that electromagnetism? 

Edited September 13, 2017 by mikegarrison

[kerbiloid]

6 hours ago, Green Baron said:

He, don't get too bold !

Rather than you, I bring arguments and references on scientific sources.
While that "gravity is a property of mass" is a quote from Aristotle's scholastics "fire rises up, while ground falls down because this is their natural property".
I'm very glad that somebody still considers Aristotle as a physicist and refers to his fantasies, but instead you could just say "gravity - it's a kind of magic".

Upd.
Equivalence principle and Hamiltonian mechanics are still in order.

Edited September 13, 2017 by kerbiloid

[Green Baron]

22 minutes ago, kerbiloid said:

Rather than you, I bring arguments and references on scientific sources.

It is rather you that should reconsider his view than others that you are putting here as having a necessity for reading schoolbooks ! You write nonsense and are patronising and unsusceptible to what others have presented to you, basic school knowledge about the four forces. I have the feeling you compensate a little with taunting others and therefore said "Don't get too bold !" and i stand to that.

Here's one of your gaps: for example you said that that relativity did not show up in the 19th century but in the 20th. That is nonsense. It showed up in the 16th century and was first formulated basically by Galilei. Gauss delivered the mathematical principles, though he maybe wasn't fully aware of the consequences and Kant laid out a philosophical base.

Edited September 13, 2017 by Green Baron

[kerbiloid]

9 minutes ago, Green Baron said:

you said that that relativity did not show up in the 19th century but in the 20th. That is nonsense. It showed up in the 16th century and was first formulated basically by Galilei.

So, you don't distinguish Galilei's "Relativity principle" for inertial system and Einstein's "Relativity theory", using Lorentz, Poincare and Minkowski works?
Relativistic mechanics has appeared in XIX, replacing/extending the classic mechanics.
Well, Aristotle and Galilei are exactly thsse people who should be brought as an example in a discussion about gravity.

So, please, familiarize yourself with Equivalence principle and Hamiltonian mechanics.

Edited September 13, 2017 by kerbiloid

[Steel]

Ok let's calm this down a little, this is getting close to personal insults.

[Green Baron]

Yeah, sorry, i don't like being scoffed at like that.

 

Any physicist here who could check that ?

- Gravity is the weakest of the fundamental forces. (I mean this is trivial.) It only overcomes the others at very high masses.

- There is no difference between inertial and gravitational Mass, only the method of measurement. This makes the concept of the reference frame  possible, the unability to tell if we are standing on ground or flung around in a centrifuge if we experience a gravitational force; or if we are floating without forces in space or falling towards another mass (inertial or non-inertial frame). Sperm whale and petunia bowl ;-)

- This leads to: gravity is a property of mass. Is this too daring a claim ? If there is no mass, there can still be space (radiation for example), but no gravity. Add mass, and things like acceleration have a meaning.

- To further explain gravity and unite it with the other forces, a ToE must be dug out.

 

Edited September 13, 2017 by Green Baron
corrected

[p1t1o]

5 minutes ago, Green Baron said:

- This leads to: gravity is a property of mass. Is this too daring a claim ? If there is no mass, there can still be space (radiation for example), but no gravity. Add mass, and things like acceleration have a meaning.

Just popped into my head - a sufficient quantity of EM radiation in a volume has zero mass but *does* exert gravity (see: Kugelblitz, a hypothetical black hole formed purely from EM radiation).

How does that change things?

[Green Baron]

7 minutes ago, p1t1o said:

Just popped into my head - a sufficient quantity of EM radiation in a volume has zero mass but *does* exert gravity (see: Kugelblitz, a hypothetical black hole formed purely from EM radiation).

How does that change things?

I think Kugelblitze are just hot plasma trapped dynamically and no black holes. They live a few seconds, radiate light and warmth, then pop and are gone (leave a bit for cleaning behind ...). No black hole. At least that's what i heard from someone who saw one, and it would fit much better what physics have taught us ;-)

As for the radiation has gravity thing, could you poke my nose to something describing that closer ?

 

Edited September 13, 2017 by Green Baron

[Steel]

23 minutes ago, Green Baron said:

Any physicist here who could check that ?

- Gravity is the weakest of the fundamental forces. (I mean this is trivial.) It only overcomes the others at very high masses.

- There is no difference between inertial and gravitational Mass, only the method of measurement. This makes the concept of the reference frame  possible, the unability to tell if we are standing on ground or flung around in a centrifuge if we experience a gravitational force; or if we are floating without forces in space or falling towards another mass (inertial or non-inertial frame). Sperm whale and petunia bowl ;-)

- This leads to: gravity is a property of mass. Is this too daring a claim ? If there is no mass, there can still be space (radiation for example), but no gravity. Add mass, and things like acceleration have a meaning.

- To further explain gravity and unite it with the other forces, a ToE must be dug out.

 

Well luckily I have a physics degree!

Gravity is the weakest of the four forces. There is no argument about that. Just because gravity has a greater effect on the large-scale structure of the universe and has longer range than the strong and weak forces does not change the fact that the gravitational interaction is the weakest (as can be seen by its tiny coupling constant).

There could be a difference between the two mass types but we just don't know (it's a big unanswered question in physics). No experiment has ever found a difference, but that does not necessarily mean that they are the same.

Technically, gravity (at least Gravity in GR) is a result of the curvature of spacetime due to local energy-density. This does not specifically have to be mass, so you can't really say that gravity is a property of mass.

To unite the forces we need a ToE. We don't necessarily need a ToE to understand more about them, however. Also, there is the possibility that a ToE that describes our universe simple doesn't exist.

Edited September 13, 2017 by Steel

[Terwin]

5 minutes ago, Green Baron said:

As for the radiation has gravity thing, could you poke my nose to something describing that closer ?

 

e=mc^2 thus m=e/(c^2)

It takes a lot of it, but you put enough high-energy photons together and you get a m where g>c

[Green Baron]

8 minutes ago, Terwin said:

e=mc^2 thus m=e/(c^2)

It takes a lot of it, but you put enough high-energy photons together and you get a m where g>c

Yes. I have a mass then and thus gravity. That's clear to me. But the point was to have very much energy without mass.

9 minutes ago, Steel said:

Technically, gravity (at least Gravity in GR) is a result of the curvature of spacetime due to local energy-density. This does not specifically have to be mass, so you can't really say that gravity is a property of mass.

 

Then comes the next question: what curves spacetime other than mass (or acceleration, which needs a mass to accelerate) ?

Edit: nevermind, the stress-energy-tensor. I think i got it !

Edited September 13, 2017 by Green Baron

[Steel]

11 minutes ago, Green Baron said:

Then comes the next question: what curves spacetime other than mass (or acceleration, which needs a mass to accelerate) ?

In the Einstein field equations (equations of GR), the curvature is a direct result of a thing called a stress-energy tensor. This is a slightly tricky thing to explain, but it essentially represents the amount of energy and momentum at each point in space. So broadly speaking, anything that contributes to this tensor curves spacetime, this can be mass, electromagnetic fields or anything else that changes the flux of momentum or energy.

Edited September 13, 2017 by Steel

[Green Baron]

Got that, next question: isn't GR, especially the reference frame thing, based on the assumption (or demanding that) that the two masses are the same ? Which experiment could possibly reveal a difference ? And, before that goes to far again: this universe, this configuration.

[Steel]

7 minutes ago, Green Baron said:

Got that, next question: isn't GR, especially the reference frame thing, based on the assumption (or demanding that) that the two masses are the same ? Which experiment could possibly reveal a difference ? And, before that goes to far again: this universe, this configuration.

Yes GR is built upon them being equivalent. Thus any experiment that might prove that they are not equivalent would also prove that GR is not a universal law, but instead something that only works in the limited scope that we have observed up to this point.

 

TL;DR: As long as GR holds, it is very likely that they are equivalent.

Edited September 13, 2017 by Steel

[kerbiloid]

1 hour ago, Green Baron said:

Any physicist here who could check that ?

Should I scan my diploma?

45 minutes ago, Green Baron said:

I think Kugelblitze are just hot plasma trapped dynamically and no black holes.

Kugelblitz has nothing common with plasma. Plasma is ionized particles, Kugelblitz is photons. And it is not trapped by a black hole, it is the black hole.

39 minutes ago, Steel said:

There could be a difference between the two mass types but we just don't know (it's a big unanswered question in physics). No experiment has ever found a difference, but that does not necessarily mean that they are the same.

(... and all below, except "the weakest").

Exactly.

Edited September 13, 2017 by kerbiloid

[Green Baron]

https://en.wikipedia.org/wiki/Ball_lightning#Proposed_scientific_explanations

[Steel]

2 minutes ago, Green Baron said:

https://en.wikipedia.org/wiki/Ball_lightning#Proposed_scientific_explanations

Kugelblitz and atmospheric ball lightning are very different things.

[Green Baron]

Really ? In this case i meant a ball lightning above and stay out of the discussion of "Kugelblitz" because Kugelblitz in German means ball lightning.

Edit: seems to be a translation thing.

Kugelblitz is a German word and means ball lightning. I have never before heard it being used in conjunction with something different than the meteorologic/atmospheric thing. But that's just me :-)

That's probably a plasma. A spectrum and video of a ball lightning is online i see.

 

But apparently Kugelblitz describes an astrophysical occurrence as well, that forms a microblackhole.

Edited September 13, 2017 by Green Baron