# B Few Questions from a hobbyist

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1. Oct 23, 2015

### George Akba

Hello, I'm not an Academic, I love physics as a casual hobby. So I have few questions that stuck in my mind. Here is the first one:

By Einsteins General Relativity everything including us stuck to Earth by gravity. Earths mass bends the Spacetime. The gravity means: deformed space is pushing us down. So if we take Spacetime out of equation just to conduct an imaginary experiment, and leave people, buildings and everything on Earth with no Spacetime present, everything will float in weightlessness?

Will there not be noticeable force between us and Earth?

I'm open to corrections.

2. Oct 23, 2015

### phinds

Since the things you mention (Earth, etc) exist in space-time, the concept of "taking away the space-time" is not a meaningful concept even in a thought experiment. It is not meaningful to ask "what would the laws of physics say about <insert nonsense of your choice> if the laws of physics did not apply".

3. Oct 23, 2015

### Mister T

It's really just about using two different ways to model gravity. As a force or using a 4-dimensional spacetime geometry. They are just different models.

In the spacetime geometry model it's not correct to say that space is pushing us down, because pushing would be the application of a force.

Concerning the removal of spacetime, space and time are human inventions. Creations of the mind. I guess you can remove them from your mind. Doing so would not remove gravity because gravity is a naturally-occurring phenomenon. Humans didn't invent gravity, we just invented different ways of describing it.

4. Oct 23, 2015

### phinds

I disagree completely. Space and time (space-time) are reality, not inventions of our minds. The ways we describe them are our inventions but they are pretty good and give reliable results regarding reality.

5. Oct 23, 2015

### George Akba

Second question: If we hypothetically make a wormhole from the centre of the universe to the very edge, then pass an object through it. Will object pass through the wormhole literally instantly, or with a delay of measurable time?

6. Oct 23, 2015

### phinds

Second question that is not meaningful because there IS no "edge" to the universe. Also, wormholes are most likely a mathematical fiction.

7. Oct 23, 2015

### George Akba

I would like to thank you Mister T, and phinds for a reply in such a short time :-)

Mister T I apologise if misunderstood you, but if I understand you correctly, then I would like to point out to you that there is an organisation in Britain that corrects time on Satellites because difference in time between orbit and Earth, caused by space being bent less at the orbit. Secondly I would mention gravitational lensing.

Looking forward hearing from you.

8. Oct 23, 2015

### phinds

I don't understand if there is a question in there somewhere but consider this:

Time passage is a bit of a complex issue. Time on a satellite passes on the satellite at the same one second per second as does time here on Earth, BUT, the satellite is (1) farther outside the Earth's gravity well, so a compensation is required for gravitational time dilation and (2) traveling at a modest speed relative to us (unless it's a geosynchronous one) and so requires a compensation for time dilation due to relative motion.

These concepts are crucial to the proper working of the GPS system since if they were not accounted for your GPS would have you driving into the sides of buildings and off into corn fields.

As I recall, the specific compensations are -7 microseconds per day for motion and +45microseconds per day for gravity.

Google the "Twin Paradox" for more on this kind of thing.

9. Oct 23, 2015

### George Akba

Reply to second question. Let point B not be an edge of the universe but be 46 bil light years away - what they call the edge of an observable Universe. My question still remains same: Will object pass through the wormhole literally instantly, or with a delay of measurable time?

Wormholes are not fact, but theoretically explainable as if we assume that Spacetime is flexible enough to bend, we can theoreticaly assume that under extreme theoretical force Spacetime will loose integrity, thus creating a hole. We could assume that in tunnel - hole is no spase hence nearly instant travel.

Thanks.

10. Oct 23, 2015

### Mister T

Note that I didn't say they aren't real!

All of the quantities in physics are things that we measure. Humans invented the tools we use to measure them. Without a way to measure them we have no way of defining them.

My apologies to the OP, I didn't mean to hijack the thread. I just wanted to clear up the misconception embedded in the original post.

11. Oct 23, 2015

### Mister T

No doubt! Without that kind of accurate time-keeping the GPS system wouldn't work. But those are part of the process needed to keep time accurately. To call them corrections implies that some prior errors were made. Yes, the engineers use the Einsteinian 4-dimensional spacetime model because the Newtonian force model is not adequate. The former is no doubt the better model. But it's still a model. It doesn't incorporate quantum theory and physicists seek a model that's better yet.

Radar-ranging is another. Radar beams that graze the surface of the sun before and after bouncing off Venus are one of the best confirmations of Einstein's physics.

12. Oct 23, 2015

### George Akba

Thanks phinds for describing the Time passage in more accurate way than I did.I skimmed through Wikipedia and read about time Gravitational time dilation.

13. Oct 23, 2015

### davenn

sorry but what you said .....

....... couldn't be taken any other way and is completely incorrect

Please be a little more careful in how you word things, it can lead people astray when they are still learning and don't recognise when something said is wrong

many thanks
Dave

14. Oct 23, 2015

### George Akba

Thanks.

15. Oct 23, 2015

### Mister T

There were no errors in what I said. Things that are human inventions are things that are real. The two are not mutually exclusive.

16. Oct 23, 2015

### davenn

Space and time exist, they are NOT human inventions

please stop compounding your error

17. Oct 23, 2015

### phinds

Spacetime "bending" is another one of those English language translations of math that really don't serve reality well. It is a totally artificial analogy based on Euclidean Geometry rather than try to explain to laymen the Riemann Geometry that describes spacetime. Things that are described as "bent" or "curved" are so described because that description uses Euclidean Geometry but in reality those things are traveling in straight lines (technically, "geodesics") in Riemann Geometry and there is no "bending" involved.

18. Oct 23, 2015

### Mister T

What makes you think that being an invention and existing are mutually exclusive?

I explained that I made no error.

19. Oct 23, 2015

### George Akba

I would like rephrase the first question: Is the Spacetime with it's deformed (imaginable) curvature deciding factor that causes gravity?

Does mass of Earth play no other role than deforming Space time thus creating a Gravity well?

Does Earth's matter (fundamental forces + energy of whole Earth) not play role in Gravitational attraction of us and everything on Earth?

What is the official scientific way of describing Gravity as an effect? Could you please explain it to me in simpler terms understandable to Hobbyist.

Thanks to all of you for your time.

20. Oct 23, 2015

### George Akba

Thanks

21. Oct 23, 2015

### phinds

Gravity is a "force" only in classical physics, which only describes reality to a limited degree. Reality is more fully described by General Relativity in which gravity is simply the creation of space-time geodesics by mass. Things, in the absence of any force applied to them, follow the geodesics. When you are standing on the surface of the Earth, you can draw a straight line (in both Euclidean AND Riemann Geometry as it happens in this case) from you to the center of mass of the Earth. Your body is doing it's best to follow that Geodesic but the ground is stopping it. In the absence of the ground, for example were you standing in mid-air up 1000 feet, you would move towards the center of mass of the Earth.

The creation of the space-time geodesics is almost always described as "bending" or "curving" space-time, or somewhat more correctly I always think, "distorting" space-time but that's using English to describe something that's best described with math. That often happens in physics. Human language is often not the most accurate way to described reality at the level of cosmology (the very large) and quantum mechanics (the very small) because Human language did not evolve in either of those conditions.

@George Akba, this hit-and-miss approach to physics via random questions on an internet forum is a really poor way to try to learn about this stuff because it will leave gaping holes in your knowledge. It's best to read through a step by step discussion of these things, even if it is only at the level of pop-sci with little math. At least you'll get all the concepts and then you can ask much better targeted questions.

22. Oct 23, 2015

### George Akba

With the third question I hope I will nut insult anybody:-)

Why (if I correctly understand present model) is electrons angular momentum one of the deciding factors that electrons not fall on proton despite having an opposite charge. Same applies to positron in antimatter.

When it comes to neutrinos with no charge or mass, there is no "Orbit", proving that electrons charge does play a role of kipping it "bounded" to a proton.

Its hard for me to grasp a "Conserving energy and momentum in nonlinear dynamics"

In Isotopes you may end up with more protons than electrons, the charge balance - force changes in favour of protons yet electrons stay "bound" in same "energy bubble"

Other than that I'm wondering about: is there any other factor than just Momentum between Leptons and Baryons that could play role in counteracting an unbalanced electromagnetic force in Isotopes.

Thanks

23. Oct 23, 2015

### Staff: Mentor

Technically, an electron doesn't 'fall on a proton' because of its wave-like properties, not because of its angular momentum. What happens is that electrons, being fermions, cannot occupy the same state as other electrons, which forces them to spread out into different orbitals when bound to atoms. If they were bosons instead, they would all pile up in the lowest-energy state, which would still not be 'on top' of the protons. But even that isn't really a correct way of describing the position of the electron, as it actually has a non-zero chance to be found inside the nucleus. It just isn't bound inside the nucleus because it doesn't interact via the strong force and the EM force isn't strong enough to confine it to that small of a space.

Angular momentum comes into it because the 'spin' of a particle determines whether that particle is a fermion or a boson. Fermions obey the exclusion principle while bosons do not. The reasons for this are too complicated for me to explain. Perhaps someone else can.

Of course. The electrons wouldn't stay bound to the atom if they weren't attracted to the protons through the EM force.

Not true. Different isotopes of an element have a different number of neutrons but still have equal numbers of protons and electrons (when neutral).

24. Oct 24, 2015

### George Akba

"In general relativity, a geodesic generalizes the notion of a "straight line" to curved spacetime. Importantly, the world line of a particle free from all external, non-gravitational force, is a particular type of geodesic. In other words, a freely moving or falling particle always moves along a geodesic.

In general relativity, gravity can be regarded as not a force but a consequence of a curved spacetime geometry where the source of curvature is the stressâ€“energy tensor (representing matter, for instance). Thus, for example, the path of a planet orbiting around a star is the projection of a geodesic of the curved 4-D spacetime geometry around the star onto 3-D space."

I general relativity Geodesic projection is defined by "stressâ€“energy tensor (representing matter, for instance)" being source of curvature. I assume matter is one of the deciding factors that shape Geodesic projection. This brings matter to a closer relationship with Gravity.

"The (special Relativity) theory is "special" in that it only applies in the special case where the curvature of spacetime due to gravity is negligible.[5][6] In order to include gravity, Einstein formulated general relativity in 1915. (Special relativity, contrary to some outdated descriptions, is capable of handling accelerated frames of reference.[7])"

If we go by special relativity and assume that: "the curvature of spacetime due to gravity is negligible" we are left with matter.

Thanks.

25. Oct 24, 2015

### George Akba

Thanks, for interesting insight, and correcting me on Isotopes. I will look more in to Isotopes as it is interesting how addition of neutrons affect or not affect relative balance in atom. Unstable Isotopes are even more fascinating.

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