Subatomic vs Gravitational forces

[zeffur7]

It has been said that electromagnetic force attracts electrons and protons to one another, while planets and celestial objects are attracted to each other by gravity. A fundamental property of matter is that matter attracts other matter to itself. If this is true, then why do we consider the electromagnetic force and gravitational force to be so different?
I understand the internal energies are hugely different between atomic bodies & celestial bodies, but they are both composed of matter. Any thoughts are welcome.

Thanks in advance.

 

[Ryan_m_b]

There are "en.wikipedia.org/wiki/Fundamental_interaction"[/URL] (of which electromagnetic and gravity are just two) and they have very different properties.

 

[zeffur7]

The other 2 are the nuclear forces, but your response isn't exactly a specific answer to my question. Both forces (subatomic & gravity) are attractive. What exactly are the differences? One difference that I can think of is that subatomic particles don't usually collide with each other unless extreme forces drive them together, whereas planetary bodies would collide if close enough to each other.

 

[Pengwuino]

Electromagnetic charges can also repel. There is a huge difference.

 

[Ryan_m_b]

I'm not an expert, I'd suggest you read through the relevant wiki articles. What I can think of is that electromagnetism is mediated by the photon whereas we do not know what mediates gravity, gravity is far weaker and electromagnetism forms in the familiar magnetic field whereas gravity is homogeneous.

Electromagnetic charges can also repel. There is a huge difference.

EDIT: Can't believe I forgot that one.

 

[Couchyam]

Another major difference comes from the fact that gravitational fields are responsible for the geometry (distances between points) of the universe, while electromagnetic fields and the particles that mediate them are accurately described acting on relatively flat (where the pythagorean theorem holds) backgrounds with Quantum Field Theory. The same approaches that were used to describe interactions between particles in QFT fail pretty miserably when applied to gravitational fields. As far as I know, string theory tries to establish the most symmetry between the fundamental forces by expressing them as emergent properties of more general interactions between dimension<=10 "branes", so you might try to read about it there.
However, you are correct in indicating that there are lots of similarities between the two different kinds of fields in classical physics: both systems radiate energy from accelerating particles, and the governing equations are similar in form (although those for gravity are far more complicated in the GR representation than those for E&M).

 

[zeffur7]

... (although those for gravity are far more complicated in the GR representation than those for E&M).

"E&M" = energy & matter, electrical & magnetic, or something else?

 

[zeffur7]

On a side/related tangent...

Suppose we built a planetary-sized object in the middle of no where (e.g. at the edge of the known universe or within the interstellar medium/space) by starting with one atom & continuously adding a stream of atoms to it until it had the same mass as our sun.

1. Do you think the body gradually curves space-time as its mass increases or it reaches a certain density & then whap! space-time curves--kind of like breaking the sound barrier (i.e. a sudden event occurs, rather than a gradual deformation of space-time)?

2. If we continued to increase the mass of the body, what happens to the whole space of the universe? Does it stretch like a sheet of latex, like when we place a heavy mass in the center of the sheet (i.e. just stretching in the middle)? Or, is there a universal stretching of space as the mass of the body continues to increase? If the latter, is there any theory that describes the limits of spatial stretching/distortion/deformation? I'm guess that the space-time deformation is like a sheet of latex (i.e. when the mass is small, it affects only the latex in the center of the sheet, but as the mass increases, more of the latex sheet gets stretched). I'm also wondering if a very large mass in space would eventually punch through space somehow (perhaps a black hole does this) like a large enough mass would eventually cause a thin latex sheet to break. Then the next question is... if that break in space occurs, where does all the matter-energy go beyond the break point? I've wondered if it may go into another dimension or into an adjacent universal bubble or perhaps it creates a new universal bubble.

3. If all mass is moving away from the center of the universe (where the big bang occurred), does the increase of mass in our hypothetical location in space affect the other bodies that are accelerating away from the center of the universe? If yes, in which way/s & how much? And by the way, into what medium are those accelerating bodies going? Is there any known or theoretical limit to the space in outer space?

Curious to know your thoughts... sorry if this seems to be leading to what should be different thread.

 

[WannabeNewton]

Where does the extra mass come from? It can't just be added in from nowhere, that clearly violates physical law. If the masses are coming in from r = infinity, and the gravitational field they generate is weak, then you can linearly superpose them to first order and say the field is getting stronger and this is basically Newtonian in principle. If the masses coming generate a strong field then the interaction is too complicated to put in words. One thing you should know is that the universe is not a sheet and there is no absolute center of the universe.

 

[Pengwuino]

1. Do you think the body gradually curves space-time as its mass increase? If not, then at what point (time or mass) do you think space-time begins to show space-time deformations.

2. If we continued to increase the mass of the body, what happens to the whole space of the universe? Does it stretch like a sheet of latex as a heavy mass is added to the center of the sheet (i.e. just in the middle)? Or, is there a universal stretch in universal space? If the latter, is there any theory that describes the limits of spatial stretching?

3. If all mass is moving away from the center of the universe (where the big bang occurred), does the increase of mass in our hypothetical location in space affect the other bodies that are accelerating away from the center of the universe? If yes, how much. And by the way, into what medium are those accelerating bodies going? Is there any known or theoretical limit to the space in outer space?

Curious to know your thoughts.

1) It's a continuous process; the deformation starts when the first mass is there.

2) What do you mean the "whole space" of the universe? It sounds like you should just learn about general relativity

3) There is no "center of the universe" and there is no medium that all the mass in the universe is expanding into.

 

[Drakkith]

1. Do you think the body gradually curves space-time as its mass increase? If not, then at what point (time or mass) do you think space-time begins to show space-time deformations.

Yes, all mass curves space time, so the curvature of the area would gradually increase as you bring more mass.

2. If we continued to increase the mass of the body, what happens to the whole space of the universe? Does it stretch like a sheet of latex as a heavy mass is added to the center of the sheet (i.e. just in the middle)? Or, is there a universal stretch in universal space? If the latter, is there any theory that describes the limits of spatial stretching?

The curvature falls off at a distance, so the effects are negligible beyond a certain distance for the amount of mass you are talking about. While the image of a large object sitting on a sheet of rubber isn't exactly correct, it is a good way to visualize the effect. As far as I know there is no limit to how much spacetime can be curved. (The effects is curvature of spacetime, not stretching of, which is one downfall to the 2d rubber sheet picture)

3. If all mass is moving away from the center of the universe (where the big bang occurred), does the increase of mass in our hypothetical location in space affect the other bodies that are accelerating away from the center of the universe? If yes, how much. And by the way, into what medium are those accelerating bodies going? Is there any known or theoretical limit to the space in outer space?

There is no center of the universe. The big bang occurred everwhere in the universe all at once, it was not an explosion in space. Spacetime itself did not exist before the big bang, so there was nothing for the universe to expand into. The view of the expansion of the universe does NOT require that it be expanding INTO something, it is simply that all points in space get further apart as time goes on.

 

[zeffur7]

1)

2) What do you mean the "whole space" of the universe? It sounds like you should just learn about general relativity

3) There is no "center of the universe" and there is no medium that all the mass in the universe is expanding into.

By "whole space of the universe", I was referring to all of the space within the universe.

It seems to me that for all visible celestial bodies to be moving away from each other, there has to be a starting point--like the center of a bomb that causes all parts of the bomb to move away from the center of the explosion.

 

[Drakkith]

By "whole space of the universe", I was referring to all of the space within the universe.

It seems to me that for all visible celestial bodies to be moving away from each other, there has to be a starting point--like the center of a bomb that causes all parts of the bomb to move away from the center of the explosion.

Nope. Understand that if you were 1 billion light years away from Earth on another planet or whatever you would ALSO see everything receding from you. The effect is identical no matter where you are at in the universe. The distance between any point in space and any other point in space is always increasing.

 

[WannabeNewton]

There is no absolute center. One condition we take into account when modeling the universe is isotropy: there cannot be, within the universe, a preferred direction. Any observer has to be able to call his point the center such that the universe looks roughly the same in all directions around that point and he/she can say that everything is moving away radially from him. If there was an absolute center then obviously there is a preferred direction which does not satisfy the condition of isotropy.

 

[zeffur7]

One thing you should know is ... there is no absolute center of the universe.

Our planet revolves around our sun, our sun revolves the center of our galaxy, doesn't our galaxy revolve around something... or is it just stuck in one place within the universe?

Where did the big bang occur and into what did it expand? Did the energy & matter in that explosion not move outwards in all directions from the origin of that bang?

 

[zeffur7]

Nope. Understand that if you were 1 billion light years away from Earth on another planet or whatever you would ALSO see everything receding from you. The effect is identical no matter where you are at in the universe. The distance between any point in space and any other point in space is always increasing.

Suppose you could put a box around the universe. If every body is moving away from every other body within that system, then there must be an origin from which those bodies originated.

Also, if all bodies are moving away from each other as you have indicated, then how can collections of bodies collide with other collections of bodies (e.g. galaxies colliding with other galaxies or galaxies (or parts of galaxies) being pulled into black holes?

 

[Drakkith]

Our planet revolves around our sun, our sun revolves the center of our galaxy, doesn't our galaxy revolve around something... or is it just stuck in one place within the universe?

Where did the big bang occur and into what did it expand? Did the energy & matter in that explosion not move outwards in all directions from the origin of that bang?

From the point of view of a galaxy 10 billion light years away we are receding from it. AND from another galaxy directly opposite of the 1st from Earth's view we are also receding from it as well. One cannot define a position in space without referring to another position.

The big bang was not an explosion in space. While we cannot really know for sure what happened AT the big bang, we can make logical conclusions about what happened directly afterwards. The universe expanded and cooled, and that expansion does not mean that the universe is expanding INTO something. It merely means that all points in space are receding from all other points.

Per here: http://en.wikipedia.org/wiki/Big_bang

There is little evidence regarding the absolute earliest instant of the expansion. Thus, the Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it describes and explains the general evolution of the universe going forward from that point on

 

[zeffur7]

From the point of view of a galaxy 10 billion light years away we are receding from it. AND from another galaxy directly opposite of the 1st from Earth's view we are also receding from it as well. One cannot define a position in space without referring to another position.

The big bang was not an explosion in space. While we cannot really know for sure what happened AT the big bang, we can make logical conclusions about what happened directly afterwards. The universe expanded and cooled, and that expansion does not mean that the universe is expanding INTO something. It merely means that all points in space are receding from all other points.

Per here: http://en.wikipedia.org/wiki/Big_bang

"According to the theory, the universe was once in an extremely hot and dense state that expanded rapidly (a "Big Bang"). As there is little consensus among physicists about the origins of the universe, the Big Bang theory explains only that such a rapid expansion caused the young universe to cool and resulted in its present continuously expanding state." http://en.wikipedia.org/wiki/Big_bang

As you can see above, according to the BBT, the universe expanded rapidly & continues to expand. To expand, it has to expand into some thing (i.e. space).

According to the same wiki article:
"Cosmologists now have fairly precise and accurate measurements of many of the parameters of the Big Bang model, and have made the unexpected discovery that the expansion of the Universe appears to be accelerating." http://en.wikipedia.org/wiki/Big_bang

The expansion of the universe appears to be accelerating. What force is causing it to accelerate? The only way for something to continue to accelerate is if the source force is continuing to affect it or if the resistance to its expansion is reduced as it cools and condenses.

How would you rationalize the above quotes with respect to your statement that the universe has no origin/center and it doesn't expand into anything?

 

[Drakkith]

The expansion of the universe appears to be accelerating. What force is causing it to accelerate? The only way for something to continue to accelerate is if the source force is continuing to affect it or if the resistance to its expansion is reduced as it cools and condenses.

How would you rationalize the above quotes with respect to your statement that the universe has no origin/center and it doesn't expand into anything?

The proposed force is usually referred to as Dark Energy. We don't know why the universe is accelerating, or why the rate of acceleration is increasing, only that it is. (Althought I believe there are several models trying to explain it) And all of that still fits exactly with the view that there is no center and the universe isn't expanding into anything.

 

[WannabeNewton]

I see nothing from those quotes nor what you said that contradicts the isotropy of the observable universe. In fact, the positive rate of change of expansion is easily seen from matter - dominated scale factor solutions to Friedmann's equations and these equations correspond to a metric that assumes isotropy.

 

[Couchyam]

Suppose you could put a box around the universe. If every body is moving away from every other body within that system, then there must be an origin from which those bodies originated.

Also, if all bodies are moving away from each other as you have indicated, then how can collections of bodies collide with other collections of bodies (e.g. galaxies colliding with other galaxies or galaxies (or parts of galaxies) being pulled into black holes?

Intuitively, it may seem that there must be a single origin from which all bodies originate if the system is expanding, especially if you are thinking of the explosion of a bomb. However, this is not always the case. Even if you assume that the universe is bounded (with finite mass and volume), it is not clear from a classical perspective that there is some unique center of mass coordinate system: this depends largely on the topology of the space your are in (for instance, set up periodic boundary conditions and suddenly the center of mass could be anywhere, depending on your coordinate system). However, we do not know if the universe is bounded by some well-defined length scale: even if we are considering only the locations of baryonic (i.e. normal) matter in space as the bounds, we still allow for the existence of vacuum energy as a parameter in our physical models, which effectively eliminates the meaning of any "center of mass" defined in a coordinate system with an infinite information capacity.

The "empirical" and consequently physical picture that we have now comes from the boundary of our own "causal horizon," which happens to indicate certain inevitable facts regardless of what picture we agree on for a background (such as the thermal regularity of the cosmic microwave background, which comes from multiple [now] causally disconnected regions of space).

EDIT: with respect to the idea of "expansion" into or out of anything else, this idea is somewhat misleading. If we lived on a donut-shaped land with no knowledge of dimensions normal to the surface, and suddenly the donut grew, we would experience "expansion" in a way that doesn't take over any "external" territory (if this doesn't seem correct, be very careful about your choice of mathematical language and or phrasing).

 

[zeffur7]

"...with respect to the idea of "expansion" into or out of anything else, this idea is somewhat misleading. If we lived on a donut-shaped land with no knowledge of dimensions normal to the surface, and suddenly the donut grew, we would experience "expansion" in a way that doesn't take over any "external" territory (if this doesn't seem correct, be very careful about your choice of mathematical language and or phrasing)."

By definition for something to expand, it has to occupy additional space. If your donut grew, it grows into previously unoccupied space--even if the space between each molecule moved a bit further apart from every other molecule. The whole donut 'must' occupy more space for it to become larger in size as it expands. If you disagree with this logic, please provide to me an example of *any* non-theoretical thing that expands without occupying additional space.

 

[Drakkith]

By definition for something to expand, it has to occupy additional space. If your donut grew, it grows into previously unoccupied space--even if the space between each molecule moved a bit further apart from every other molecule. The whole donut 'must' occupy more space for it to become larger in size as it expands. If you disagree with this logic, please provide to me an example of *any* non-theoretical thing that expands without occupying additional space.

It isn't expansion like you and I experience in normal everyday circumstances. This is similar to how the "spin" of a subatomic particle is not like the spin of a basketball even though both effects are named the same.

 

[zeffur7]

It isn't expansion like you and I experience in normal everyday circumstances. This is similar to how the "spin" of a subatomic particle is not like the spin of a basketball even though both effects are named the same.

Your response doesn't directly answer my question nor provide me with even one 'real' thing that expands without occupying additional space as it expands.

Also, if all things are accelerating & moving away from all other things in the universe as the universe expands, then in your opinion, does that mean space is expanding while physical matter remains a fixed mass & size? I haven't heard of non-Earth planets growing in mass. In fact, our sun is supposedly decreasing in mass as it converts it's mass into radiated energy that leaves it's domain.

 

[Drakkith]

Your response doesn't directly answer my question nor provide me with even one 'real' thing that expands without occupying additional space as it expands.

Also, if all things are accelerating & moving away from all other things in the universe as the universe expands, then in your opinion, does that mean space is expanding while physical matter remains a fixed mass & size? I haven't heard of non-Earth planets growing in mass. In fact, our sun is supposedly decreasing in mass as it converts it's mass into radiated energy that leaves it's domain.

You missed the point of my post entirely. Comparing the expansion of the universe to the expansion of a loaf of bread in the oven is useless, the two are not comparable except in a vague general way.

Yes, space is expanding while matter retains its size and mass.

 

[Couchyam]

consider the following example:
let there be two "letters", 'a' and 'b', which can be concatenated to form new elements in a set: any two elements of the set can be concatenated to produce a third element in the set (which is unique). Here's the following rule: you can only make one concatenation per time step. Philosophical question: is there some "space" into which this set (which is "expanding" in a way) is growing? Hypothetically, we could construct the "closure" of this set, and say that the "instantaneous" set is growing into the closure. However, from a computational perspective this would mean doing an infinite number of calculations (concatenations) in advance to determine all elements of the set. This is more of a philosophical question, but from the perspective of the elements of the set, there isn't really an "outside" set into which it is expanding: it's just making new combinations of old parts.

 

[MrNerd]

By definition for something to expand, it has to occupy additional space. If your donut grew, it grows into previously unoccupied space--even if the space between each molecule moved a bit further apart from every other molecule. The whole donut 'must' occupy more space for it to become larger in size as it expands. If you disagree with this logic, please provide to me an example of *any* non-theoretical thing that expands without occupying additional space.

I think the way it works is that at the edge of the universe is the edge of space itself. Beyond this limit, there is no space. Within this limit, there is space. Hence, space can expand into nothing.

I may be wrong, but I do admit it.

 

[MrNerd]

However, my personal theory of the Big Bang is that there were no observers. Because there were no observers, there was nothing prohibiting the existence of mass. Therefore, mass exists. I got this idea from the idea of virtual particles. They pop in and out of existence everywhere all the time. They exist for such a short period of time that the uncertainty principle enables this while still allowing conservation of mass/energy.

 

[Drakkith]

I think the way it works is that at the edge of the universe is the edge of space itself. Beyond this limit, there is no space. Within this limit, there is space. Hence, space can expand into nothing.

I may be wrong, but I do admit it.

I believe the current view is that there is no edge to the universe.

However, my personal theory of the Big Bang is that there were no observers. Because there were no observers, there was nothing prohibiting the existence of mass. Therefore, mass exists. I got this idea from the idea of virtual particles. They pop in and out of existence everywhere all the time. They exist for such a short period of time that the uncertainty principle enables this while still allowing conservation of mass/energy.

Be aware that virtual particles are a mathematical construct with no evidence that they actually exist.

 

[zeffur7]

You missed the point of my post entirely. Comparing the expansion of the universe to the expansion of a loaf of bread in the oven is useless, the two are not comparable except in a vague general way.

Yes, space is expanding while matter retains its size and mass.

If the volume of space is increasing (i.e. expanding), and all visible objects within that space just so happens to be along for the ride (i.e. all visible objects are receding from all other visible objects as the space that they occupy is expanded/moved/stretched), then how is it possible that galaxies collide with other galaxies or get sucked into black holes?