Things you'd like to ask a theoretical physicist.

Originally posted by Moduli

I've always been intrigued by the interelatedness of time and space. In your opinion is it possible for one to exist without the other?

There's no problem at all with this, they can certainly exist without each other. The way the laws of physics work, they are related to each other, though. But there was no reason it could not have been different.

Forgive me for pushing this question, but is it possible to expand on this slightly more? That way all my really big physics questions I've ever pondered will have been answered and I can sleep easy.

If time is basically change in matter, does not time need space in order for this change to take place? Whether it's change in the location - one place to another, or change in form - e.g the rearrangement of atoms or molecules, or even thought - electrical signals from here in the brain to there; I cannot see how time could exist independently of space.

Although I can see that space could exist independantly of time - e.g hypothetically if time froze, x would still be a specific distance away from y.

reply to post by zigmeister

Post edited to add: I see that my post is not even a fifth wheel on this thread; more like a sixth. Serve me right for deciding to reply the OP without reading the whole thread.

Reassuring to see, however, that I seem to have offered the same answers as the experts – well, more or less the same.

1. Given that entropy flows only forward, why is it that some people who accept entropy as a working model of time believe in predetermination, as in effect-cause, rather than cause-effect. Is it possible that entropy flows in the opposite direction, in the case of effect-cause. If so, do we not perceive it because our minds can only conceptualize why we make of our observations? Does this become paradoxical?

Entropy is called the arrow of time but it is not time itself. Time remains a mystery to physics. But why do you feel that determinsim and entropy are mutually incompatible?

I seem to remember reading somewhere that liquid helium can be negentropic under certain conditions, but I wouldn’t swear to it.

2. Does the existence of black energy affect the speed of light? If dark energy is pushing outward, does light opposing it have to travel against an opposing energy force? Does this affect how we understand the speed of light?

Dark energy. No, it does not. The speed of light remains the same, though if the source and receiver were moving apart due to dark energy or anything else, its frequency would be redshifted down in the usual way. And no, dark energy does not ‘oppose the speed of light’. If it did, the speed of light would vary depending on the direction of motion and dark energy would be called luminiferous ether.

3. Is dark matter a medium in which friction exists? Or is it spatially different from the matter we know?

We have no knowledge of the physical properties of dark matter, except (1) it has gravitational properties similar to those of ordinary matter and (2) it does not seem to interact with ordinary matter except gravitationally.

4. String theory accepts that reality consists of 11 dimensions. Most people know of the 4 that we can observe. Given that the only models (at least that I can seem to find) are mathematical, is there any way that these other dimensions can be explained in layman's terms? Is there a model which exists in which the average person can interpret?

I am sorry to say there is none. As Stephen Hawking pointed out, physicists have just as much trouble visualizing this stuff as everybody else does. Most of the time they stay with the maths and don’t bother. I recommend you do the same.

5. In quantum physics, what limits nature to the Planck Measurements?

That would be, respectively, ‘quantum mechanics’ and ‘the Planck length’. It is not a natural limit; it is an artificial minimum, arbitrarily derived from the manipulation of some physical constants. Because of its derivation, it does have some physical implications, which you can read about here, but it is not ‘the shortest possible length’ or anything like that.

Wow, thanks. I'm glad to see that this thread has grown, and there have been other questions/answers. Forgive me for asking some basic/nonsensical questions. I have a poor understanding of theoretical physics, and wished to expand upon what I can grasp. And yes, I meant dark energy. I have no idea why I put black energy. Please, keep the Q&A rolling!

If a black hole is supposedly a point of infinite density (I find this ridiculously hard to believe as the mathematical concepts of 'point' and 'infinity' do not seem to fit in a physical world), how can it have an edge and be in this physical universe?

What I mean is, if the gravitational force is subject to the inverse-square law and fades in strength the further away you get from the massive object, how can you 'fade' from infinite density to finite density? If the black hole is infinitely dense but the 'normal' universe around it is finitely dense, there must be a transitional area where infinity gradually becomes finite. Or the inverse-square law doesn't really apply to gravity.

Given that infinity isn't 'a very big number' but is beyond number, how can this mathematical concept of infinite density be considered a physical reality and be said to exist within a finite universe?

What do you believe, if any, the significance of the reoccurring themes of spirals and swirls in the universe? How that motion came about and took hold in so many assets of functions and scale? from the solor system traveling through space as a 3d wave, which would be a spiral, to the spiraling of a galaxy, to even poetically a human life, for life is linear from start to finish but full of ups and downs. you may think what is the significance of this question and i may anticipate that there are alot of factors that contribute to these wave motions and spins,
but i was just wondering if its something semi special, or just the plain ol way things are..just because.

How do galaxies move through space as a cosmic unit? what dictates direction?

if the universe is expanding, where and what are the areas the universe has not yet expanded into? are these areas of space different from the areas that galaxies have traveled through?
what im trying to understand or grasp is how there are never patches of space our solor system drives into full of supernova stuff and radiations and elements of all kind, is it more like with all the forces and laws that if their were things in space ahead of a solor system the debris or even the space it self would be moved out of the way
by the incoming solor systems velocity, gravity, and other fields.

Why do you think it impossible for the universe, its laws, functions and awesomeness to not be an accident,
if there is a creator would it not making itself clear enough to you be its flaw?
would you failing to understand its terms of brilliance be yours?
If there were an architect of physical reality would scientists not feel so personally on the cutting edge,
would it infringe on your free will or value, or ability,
is it easier to deny something so superiors existence
when without it and on this planet you are the one with the superior existence,


What do you think the best way for humanity to function on this planet is?
what do you think should be the goals of humans on this planet?
where do you think science can take us and will that be a place we should want to go?
if humans could enjoy their natural life sentence and prosper during life,
could that be more "important" then scientific advance/space travel?



scientists who believe in the big bang believe all matter and energy, and galaxy to be expanding out wardly, does that mean on the other side of the big bang and all around the epicenter there would be more or less equal blasts of matter and universe, ever expanding leaving an ever expanding space where the bang started?

the model of the big bang suggests expansion, or the evidence of redshift or is it all stars and galaxies always moving away from our position, its thought that all these matters are expanding or spreading out, moving foward in time, and evolving because it is thought that a much earlier stage all was in one state, and exploded.

is there any room for error in this, could the information of galactic shift and movement be from a more cyclical
there for eternal structure of the universe. the stuff we see moving away from us is really moving around us or with us?

if time travel is possible, lets say there are advanced races of beings that can, if scientists believe one day the universe will end, crunch something, whatever, could aliens time travel to an earlier time of the universe and repeat and live in an eternal universe voiding the significance of a universal end point if a universe ends and no one is around to see it, does it end?

if you were nothing, and could be anything in the universe existent, abstract or imaginary, what would you desiree to be.

if you were a god in-control of all matters in your own personal section of infinite space , do you think you could create a universe from a big bang?

reply to post by morkington

If a black hole is supposedly a point of infinite density (I find this ridiculously hard to believe as the mathematical concepts of 'point' and 'infinity' do not seem to fit in a physical world), how can it have an edge and be in this physical universe?

I dont think that is true, infinite density only comes from the breakdown of equations of relativity at the singularity. In reality, very high but finite density is expected.

"What your asking, while it was in your mind, might have made some sense, but when exposed to the light of day becomes Word Salad" (ALEX G.)

You might have some reasonable questions, even some that actually make sense, but to put them in laymans terms may not be so easy. I suggest you go to www.physforum.com/ it's a forum I belong to, it is quite interesting, with some incredible intelligence there. What you asking partially makes sense in the form you pose it, but don't go there playing like your anything but an interested novice, or they will cut you to ribbons. Ask questions with humility and in all earnestness and you will survive, even maybe taken under someone's wing. Know your place, and do a lot of reading there. By the way, respect Alex G. he's the man, and if you regard him as a physics master, you will learn, or he can have you disappear.... ENJOY .....Rich

PS ..... especially interesting is the Quantum mechanics section.

PSS.... please don't take my answer/suggestion as condescending

Moduli, our friendly neighborhood (self-proclaimed) String Theorist...you have returned. Good to know you're still not too good to speak to us pathetic little foot-scums.

Originally posted by Moduli

Originally posted by CLPrime
The bigger question is actually why other particles do have mass. Mass is another word for inertia, which is how resistant an object is to being accelerated. We have no idea what the source of inertia is.

This is completely incorrect. There is no dichotomy (or any other division) between mass and inertia in modern physics. You don't even need relativity do deal with this issue, good 'ol 1800s Lagrangian mechanics will settle this issue. There is only mass, and the way things move under a force is dictated by the Euler-Lagrange equations.

Mass and inertia are identical. This is not a division, a dichotomy, or even an appendectomy. This is what we in the 'know' call "equality". Mass is the observational equivalent of inertia, in much the same way as weight is the experiential equivalent of mass. I never once mentioned relativity in this discussion, because, of course, relativity has nothing to do with it. It a simple matter of definition: mass = inertia, as both are a resistance to acceleration.
I see you've gone to great lengths to sound smart with this one, but it really wasn't necessary. The Euler-Lagrange equations do, for example, model particle movement when subjected to a force, but, in that case, you surely know that the equation becomes the familiar F = ma... that is, force = mass x acceleration. Greater mass means a greater force is required to produce constant acceleration, so mass determines how resistant an object is to acceleration. Now, look up "inertia". Actually, allow me to do it for you: inertia - the property of matter by which it retains its state of rest or its velocity along a straight line so long as it is not acted upon by an external force.
Mass and inertia - one and the same.

Originally posted by CLPrime
Ironically, if gravitons exist, then they, too, produce their own gravitational field. And, then, each graviton in that field would produce its own gravitational field. And each graviton in each of those fields would produce its own gravitational field. And so on.

This is not ironic, this is the opposite of ironic. Expected, we would call it.

Actually, it is ironic. It means that the quanta of gravity produce their own gravitational fields... and the quanta of those fields then produce their own gravitational fields... and the quanta of those fields then produce their own gravitational fields... and so on. Gravitons produce gravitons produce gravitons produce gravitons produce gravitons. That sort of gravitational fractal, to me, screams "irony".

reply to post by morkington

infinite density does not equate to infinite mass.

You guys are too deep, easiest one is:

What's it like making a dump truck full of money without ever having to produce tangible results beyond the math you use to create your specific reality?

Derek

I have a question. If nothing can escape from beyond the event horizon, how come black holes can have electric charge? Charge is carried by exchange of (virtual) photons, and photons travel at the speed of light. How can mass beyond the event horizon exchange a photon with mass on the other side, when no photon can escape from beyond the horizon? Or are virtual particles not subject to gravity?

reply to post by Maslo


Significantly charged black holes don't exist because the inward gravitational force required to create a black hole would be countered by the much greater outward electromagnetic force. However, if one were able to form, its charge would not be directly detectable by an external observer (because, as you correctly point out, photons are unable to escape the event horizon of the black hole...which is what makes it a black hole in the first place).

One interesting quality of a charged black hole is its second horizon. It has the outer event horizon that we all know and love, but it also has an inner Cauchy horizon, beyond which causality (cause-effect, and the predictability of effect from cause) breaks down. Observationally, it would appear to be a basic Schwarzschild black hole, but, inside, it would be pulling some serious violations of layman logic.

reply to post by ImaFungi


If our entire universe were moving through a larger set of dimentions, then many unexplained phenomena could be anologous to somthing like the coriolis effect or electromagnetic induction. Because our whole universe would be moving through various types of enegry fields.

I think actually a number of the spiral phenomena in our universe can be attributed to turbulence and expansion, like vapors in draft of air.

Infinite means there is no way to measure it.

reply to post by Maslo


since 1 + -1 = 0, also 0 = 1 + -1

Space is constantly making pairs of anti particles which normaly attract and ahnihilate each other. At the event horizon the pairs can be split by the force the black hole and the particle that escapes would be opposite in some quality, such as charge, to the black hole.

reply to post by Semicollegiate


That would be Hawking radiation, which we have never detected the existence of. Besides, the charge of each individual virtual particle realized at the event horizon of the black hole has nothing to do with the charge of the black hole, itself, which is the charge of the object that collapsed to form it.

reply to post by CLPrime


Yes, that was from Dr. Hawking's book "A Brief History of Time".

If a black hole has a charge it would constanly attract the opposite set of particles and its charge would decrease over time. so what kind of charge does a black hole have?

reply to post by Semicollegiate


Indeed. Still, Hawking radiation is rather difficult to detect, if it exists at all. If we could detect it, though, we could certainly tell if a black hole is charged or not - the charge of the black hole being the same as the charge of the Hawking radiation (whether positive, negative, or neutral), since like charges repel.

Forgive my hasty assumption that the two had nothing to do with each other. That's what happens when you think you know it all this late at night.

ETA: I just realized why I assumed they had nothing to do with each other. My first thought was that these virtual particles would be exclusively photons, which would reveal nothing of the black hole's charge, since photons are neutral.

reply to post by zigmeister

Forgive me for asking some basic/nonsensical questions.

I don’t think they were either basic or nonsensical. And I think Moduli was unnecessarily rude to you.

How much do you know about physics? Do you remember your lessons from school? Most of physics is really about fairly mundane subjects – understanding how sound behaves inside an enclosed space, for example, or how vapour trails form behind an aeroplane, or how electrons move in semiconducting material. Most people who claim an interest in physics have no interest in that kind of thing, however; it’s always the fundamentals, paradoxes and big-picture stuff they’re interested in – gravity, relativity, quantum entanglement, black holes. The big-concept, God-only-knows stuff. But in these areas it’s hard for a layman even to ask questions intelligently.

I plead guilty of this myself, although (speaking as a former student of physics) I tend to think such subjects are neither relevant nor meaningful to lay folk, and are best left alone as almost certain to be misunderstood and cause confusion. Of course, most ATS members would probably argue that saying ‘leave it to the experts’ is just asking to have the wool pulled over one’s eyes by powerful conspirators. In scientific matters, though, and especially in physics, there’s often nothing else one can do.