SUMMARY: Theoretical physicist Dr. Lawrence M. Krauss from Case Western University and author of Hiding in the Mirror: The Mysterious Allure of Extra Dimensions, from Plato to String Theory and Beyond has agreed to answer questions from the Bad Astronomy/Universe Today forum. If you've got puzzling questions about physics, multiple dimensions, or any of his books, follow this link to the forum and post a question. We'll gather up the best questions and pass them along to Dr. Krauss to answer. I'll post his answers back in Universe Today when I get them.

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Dr. Krauss,

I attended your lecture at the Cleveland Museum on November 10, and wanted to ask this question during the book signing. I know you don't totally agree with String Theory, but my question has to due with that and multiple dimensions. If I am not mistaken String theory states that there needs to be an additional 11 dimensions. My question is; Why 11 dimensions? Why not 7 or 30 or 400?

--> Sam DiRocco

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http://firstlight.mvobservatory.com/

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Language Is A Virus From Outer Space, And When You Talk, You Just Make Sounds That, more or Less, Sync Up With Your Lips.

If there are multiple branes in the universe, in particular the two boundary branes in the ekpyrotic model, can the compactified dimensions in the two branes differ? The paper From Big Bang to Big Crunch by Khoury, Ovrut, Seiberg, Steinhardt and Turok (http://xxx.lanl.gov/PS_cache/hep-th/...08/0108187.pdf) seems to allow for the set of compactified dimensions to change in a collision between the end branes, but would the resulting metric in both end branes be identical?

Do you expect there are causal actions for probability's explanations, probably?

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Lighten up! This is a stellar board!

What are your thoughts on gravity being robust in other dimensions?

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Lighten up! This is a stellar board!

Dr. Krauss,

If cosmic strings exist, how would they effect the expansion of the universe? Could they be a major contributer of mass to Dark Matter? Thankyou.

Clear Skies,
SilverWing

Dr. Krauss, with tongue just a bit in cheek, why can't we say that an undetected photon (say, from cosmic microwave background radiation) is a perpetual motion machine? How much more than 13.7 billion years or so do we need to be called perpetual? :-)

Do atoms have memory?

Three dimensions through time I like. I can imagine how a mathematical discription of dimensions going from one to two to three leads arithmetically to infinite dimensions, but how to understand these dimensions in a real world way escapes me. Is there any help?

Dr. Krauss. I understand that the string theory is an attempt to understand
the structure of matter on a level more basic than the quark structure of the
proton and the neutron. Is the string theory now well established or is it still
just speculation?

Igor

Dr Krauss,

Can String Theory be tested and proved/disproved? If not, can we hope to have such tests by the end of the 21st century?

Hello, I saw a programme on Channel 4 (British T.V. channel) a while back about string theory. Now in it there was the question about why gravity was much weaker than the other 3 forces and a possible answer was that the gravity string was either a closed string or an open string (i.e. either a circle or a line) - I can't remember which way round it was and was different from the other forces in that they were of the other sort. Now the upshot of this difference was that gravity leaked from our universe into other universes and hence the reason was a lot weaker.

Well that got me thinking, if that was true then why couldn't gravity leak into our universe from other unoverses and if it did that's what dark matter was?

Of course there's always to chance that I picked up the what was said on the Channel 4 prog. wrongly and what I've said above is total rubbish? If not is it possible

Forgive me if I have this wrong. I have been reading about cosmology for 15 years and feel I still know precious little about it.

Anyway, if I am correct, equivalence tells us that gravity and acceleration are indistinguishable. As gravity is thought to be the consequence of the curvature of space-time, does that mean that accelerating objects cause space-time to curve? If so, is that what "frame dragging" is all about?

Dr. Krauss. I have friends who own an SUV that gets absurdly low mileage. I would like to know where I can get a gallon of inflationary spacetime, so that I can add a tiny bit to their gas tank, ...like drygas, with each fill-up. That way, since it expands carrying the matter along with it, indefinitely, and at superluminal velocity,..they can get about a million miles a gallon. (They drive a lot.).Thanks. Ciao. Pete.

P.S. When I asked this question while a visiting scientist at MIT, they laughed so hard they couldn't talk and tears came to their eyes in the particle physics labs. If you climb out on a limb,...somebody will saw it off. Pete.

Dr. Krauss. As a physics and chemistry teacher, I have given talks at American Association of Physics Teacher's Meetings, sometimes jointly held with the American Physical Society Meetings at Vassar College(92), Williams College(93), Harvard University(94), Norwich University(99), and Hartford, Pratt&Whitney Aircraft(2004). (Also talks at local Astronomy clubs in New England)Most of these have involved supernova theory in some capacity or other....their energetics, morphological characteristics of remnants, parity effects, pulsar characteristics, a solution to the Supernova Problem, neutrino forward-scattering, gravity waves, prompt neutrino bursts, galactic escape velocities for pulsars. Subliminal to these talks has been my hints at an underlying mechanism for pulsar ejections which is involved in a unified field theory I wrote some 23 years ago. ...simple, but valid. I would like to give a talk on that idea at Fermilab. Leon Lederman personally pushed for high school science teachers, and particularly physics teachers to be more collaborative with industrial-academic coalitions. Been there, done that. Boston College asked us to conduct a little piece of research ourselves to stay current. Been there,too,done that. This little talk will show the merits of encouraging such things...a high school physics teacher will reveal the only valid quantum theory of gravity yet to predict physical effects seen at six different major labs or institutions in the world. It's posted in these forums piecemeal, and you will note. I do not violate the precepts of SR or GR. I do not violate the Hierarchy of Conservation Laws. I obey Lorentz invariance, and hold others to it too. Gracious Bill Bertozzi, who ran the worlds largest particle physics group..the Nuclear Interaction Group...at MIT, said of my off-the-cuff talk ( I had 15 minutes to prepare)..on the relation of the results of the He-3 parity experiments at Bates to the parity effects in type-2 supernova pulsar ejections.."that's the kind of thinking we need going on around here(Bldg 26 lecture hall). So, I'm putting you on the spot, "Can you open the doors of Fermilab to the patient, genuine, radical thinking,near-solitary thinker, who has confounded them all? "
P.S.My letter to Leon Lederman went unanswered. My dad used to say ( I wish he was here for this as he used to letter the stalls for Man-O-War, Citation, etc..), put your money where your mouth is. Pick a horse. Buy a ticket. Go down to the rail. Feel the thundering herd go by. Watch the clods of dirt flying from their hooves. Listen to the heavy breathing of the steeds, and the cursing of the jockeys, the leather saddles creaking, and groaning. Watch the steaming, flaring nostrils....and scream em home! When you win at the track. It's simple. You cash your ticket. When you win in physics, it's not so clearcut. Ciao. Pete

PPS. In the New England forum I will give similar talk locally, as a memory to Al Rosenburg of Keene State for his help as chair of the Williams event.

What's beyond the Universe ? And what about the inner side ?

How is time "percieved" by a photon? Does time come to a halt in its frame of reference? How many dimensions would it move in?

Thanks

Doctor Krauss,

My question may seem a bit whacky.

Is there a simple experiment or observation to prove that the following scenario is not possible?

Rather than the current belief that gravity is an attractive force - gravity is actually a repulsive force.

Consider the following possibility:

There is a repulsive force (per unit volume) in the whole universe and/or possibly external.

This force interacts weakly with matter and is also weakly attenuated as it passes through matter.

Rather than objects being pulled to each other because of their inherent mass, they are actually pushed together. This happens because as the force interacts with matter and is attenuated by it, a “shadow effect” is created between objects causing an unequal “Push” in the volume between the objects. The “push” between the objects is smaller than the “push” from all other directions. Thus the objects come together.

Depending on the degree of interaction and attenuation between this “force” and matter, this “force” could possibly be extremely large.

Sound whacky? Sure, but is there an obvious way to show that it IS whacky?

Richard Dils

At the Big Bang, the three spatial dimensions “suddenly” began their explosive expansion. Was time also undergoing an explosive expansion of its own? Is this explosive expansion merely what we call the passage of time? Or was time not simply passing but changing the pace at which it passed? Scientists speculate that the universe underwent a period of rapid expansion and then slowed; would it mean anything different to say that time proceeded at a very lethargic pace and then sped up? Or it more than just definitional that time is viewed as a constant?

It seems to me that we only recognize spatial expansion because it is counteracted by gravity (keeping large things like galaxies and solar systems from expanding) and the other forces (keeping atoms, molecules and perhaps me from expanding). Is time similarly constrained by local forces?

Would it be correct to say that at the "moment" of the Big Bang a near-infinite mass was compressed into a single point, and, if so, wouldn’t that produce a nearly infinite warping of space? Is expansion the same as the un-warping of space as mass disperses? Or does the rapid dispersion of mass quickly pass the point where space is (at least with regard to its warping by gravity) for all intents and purposes flat, so that from here on the universe's expansion is independent of the lessening of the warping effect? Is this point reached in microseconds after the Big Bang... seconds... minutes... millions of years? Or is the Universe's expansion merely an eternal un-warping? (And could this be true of time as well?)

Finally, do you remember Kurt Vonnegut's "Slaughterhouse Five," where he suggests that the dimension of time's apparent uniqueness only exists because we are "stuck" in it, like a person tied to the front of a locomotive is stuck moving in one direction through space. Is it a reasonable conjecture that the uncontrollable passage of time is an artifact of our subjective perspective? Further, could the singular direction of entropy be due to our position with respect to the Big Bang, just as the singular direction of gravity is due to our position with respect to the center of the Earth? (Of course, the fact that the Big Bang has no location in space but only in time -- that the universe has no center but does have a beginning -- does mean that time is objectively unique in some ways.)

In short:
1. In the moment of the Big Bang, were time and space almost infinitely warped by the gravitational effect of this concentration of near-infinite mass, and was/is the expansion of the universe partly or completely the process of space (and perhaps time) un-warping and flattening out?
2. The idea that the universe underwent a phase of rapid expansion, which then slowed, seems to imply that spatial expansion is variable but that time proceeds at a constant rate. Is that in fact the case?
3. We only recognize expansion because it is not uniform; gravity and the other forces keep galaxies, atoms and me from expanding along with the universe. Is the expansion/passage of time similarly inhibited by these forces?
4. Time is certainly unique in that the Big Bang has a unique location in time but not in space. However, is it possible that part of time's apparent uniqueness -- the way it passes -- is a product of subjectivity.?

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"Now therefore, behold, the LORD hath put a lying spirit in the mouth of all these thy prophets" (1 Kings 22:23)

Dr. Krauss,

The second law of thermodynamics indicates that heat/energy flows from greater to lesser potential, ie increased entropy. Indicative of this is that stars and planets emit heat. Does this mean the ambient background energy content of the universe is increasing? If so, can the change be estimated/measured?

If the rate that the universe is expanding is accilerating is there a formula that describes the rate of expansion and does it resemble gravitational accileration?

Dr. Krauss,

One of the reoccurring themes on much of the Against-the-Mainstream forum is whether or not a proposed solution is testable. We argue, for example that Dark Energy has no local observables and is therefore not testable.

Should non-testable parametric assumptions be allowed in Cosmic or particle theory? If so, what is, or should be, acceptable criteria?

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jwj

It's a big universe out there...is it really unwinding, really burning out?

What is the gravity? Newton said a thing... Einstein said another thing and actual physicists what think about that?


Jorge Almeida
Viseu - PORTUGAL

Dr. Krauss, I would very much like to know what so-called Dark Matter is, as well as the oft-mentioned substance Anti-Matter. I've heard them both used in science fiction to no end, but what is the science, not the fiction, behind these two substances?

Dr. Krauss:

I have three questions about the Big Bang:

1) At the beginning, all the particles of the universe were in a very small place and they were squeezed hard. Does it mean that space inside the particles doesn't contract as the rest of the space of the universe?

2) The Thermodynamics says that the universe goes to entropy, goes to disorganization. The Big Bang says that the universe structures with the time. Isn't it contradictory?

3) If we consider that the universe is a sphere of four dimensions, three spacial dimensions and the time, the radius of the sphere is time and the surface of the sphere are the three spacial dimensions (the surface of the spheres that we see has only two dimensions but this image is useful for understanding the universe). As the space expands, the time (the radius of the sphere) expands too. If a photon is created when the universe was very young, it travels along the three dimensions (the surface of the sphere) and draws a spiral.

This model explains the relativistic example of the twins: if one of them travels across the space very fast, when he returns will look younger than the other one. We can explain this considering that any movement in the spacial dimensions will be in angle of 90° with respect to the time. Then, its moment will oppose resistence to the time vector, the time contracts (radius of the sphere) and the space correspondig to that radio contracts too (fraction of the surface of the sphere).

The space would be a membrane of three dimensions that covers a sphere of four dimensions that is inflated and taunted by the pressure of the time.

Is possible this model of the universe?
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I have a hypothesis about the atom. Tell me if I'm wrong.

I've never seen that a proton binds to other proton. It's clear because the electric charge doesn't allow that. But two protons can be bound if one them is converted in neutron through the integration with an electron.

As we see in the atoms, they can be bound to other atoms because the electric charge of the electrons isn't simetric, doesn't cover perfectly the electric charges of the protons of the nucleus (positive) and the protons attract the electrons of other atoms through the holes (in the case of helium, the electric charge of the electrons is simetric and the helium doesn't bind to other atoms).

The same thing we can think about the integration of a proton with a neutron: the distribution of the positive charge of the neutron isn't simetric and the negative charge of the electron that is inside the proton-neutron can go out through some holes.

However, this hypothesis explains why a proton and a neutron could be bound but desn't explain why when a nucleus of an atom is broken releases so huge quantity of energy. I will pretend to clear this doubt with the following ideas:

Everybody knows that when we join two hollow hemispheres and we extract the air of their interior with a pump that consumes little energy, it's impossible separate them. Then, we can think the same thing about the pressure of the time: when the proton and the neutron are very close, the pressure of the time (that fills everything) is eliminates and the particles are bound very hard. I don't mean that "something" extracts the pressure of the time with any kind of pump with the "purpose" of binding the particles. I think that this integration is the result of a inevitable physical process, as a rock that falls across a slope.

Excuse me if this sounds like fiction science.

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Other hypothesis #1:

The relativity gives the formula E=mc² that calculates de energy in function of the mass and the squared of the velocity of the light.

The energy is a sphere of three dimensions. The volume of the sphere is (4/3)PIr³. If we consider that de radius of the sphere is 1, the volume of the sphere is 4.189 and experimental value of the mechanical equivalent of the heat is 4.186. (the mechanical equivalent of the heat is a constant).

If we imagine that an electromagnetic wave is created now, it will travel through the space like the waves in a pond. But as the wave propagates in three dimensions, we obtain that the radius of the sphere is the time and the volume of the sphere is the space. As velocity is s/t (space divided by time), the velocity of the light is a constant, 4.189/1 = 4.189 (if the radius of the sphere is 1), c² = 17.546 and E = 17.546m.

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Other hypothesis #2:

If we think an electron with high energy like a globe of rubber very big, inflate and pressured, we can't see where it is because it is in the whole universe. But if we do a quantic experiment with the purpose of observe where it is, this means that we prick the globe and the whole energy goes out by the hole and we belive that the electron is there (for practical purpouses the electron realy is there). The indeterminism hapens because we do the observation when the electron is deflating. Sometime is almost inflated, sometimes is almost deflated and sometimes is in the middle.

In the experiment of the two cracks, the electron pass as wave and with our observation we tranform it in particle (if we use a screen the electron is not tranformed).

In the case of the EPR paradox, if we consider the light as particle obviously it is impossible that the photons communicated between them. But if we consider the light as a wave, the wave of light goes through the three dimensions, inclusive in the direction of the other particle and then the "photons" communicated between them. Realy, the light goes as wave and is transformed in particle with our observation.

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Other hypothesis #3:

The gravitation and the radiation compete for the space. The gravitation pretends to reduce it to a point and the radiation pretends to expand it without limit (the word radiation comes from the word radius). The radiation travels across the universe and with its movement press the space to be bigger. One is centripedal and the other one is centrifugal.

The time and the space are the radiation and the anti-time and the anti-space are the gravitation.

And we are in the middle. We are 1, between the zero and the infinite, between the death and the eternity.

Excuse me if this sounds like poetry.

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Other hypothesis #4:

The energy is the tensor that unites the the expansive force of the radiation and the constrictive force of the gravitation.

This tensor is the space, which is a strechted membrane.

When an electron is accelerated, the radiation grows, the mass grows (gravitation) and the energy grows too with the "purpouse" of keepping them united.

The indeterminism can be explained if we consider that an electron that travels is stretched by the forces radiation and gravitation. If we want calculate its exact position with must reduce the velocity because the electon is stretched and if we want calculate the velocity we must increase the velocity with the purpouse to have more exact measurement between the initial position and the final position. Then, we stretch the electron and its exact position is lost. I don't how measure exactly the initial position and the final position, but the idea may be useful.

The electron is a synthesis of the gravitation and the radiation. The mass pretends reduce it to a point and the electric field pretends expand it upto the limits of the universe. The space between them is the energy of the electron.

Like is said in the former idea, the electric field is a pressure to outward and, it's logical, the electric field of the all the electrons will clash. As a result, they will reject among them.

This explains why the particles of the same charge reject among them, but not why the particles of different charge attract among them.

Certainly if we consider only the three spacial dimensions the arena where the particles interact, necessary all them will clash. But if we remember the time dimension, the values of the charged particles vary in this dimension and they don't clash. So, as the repulsion is eliminated, the gravitation will join the particles, the electric charge doesn't exist and is replaced by the radiation and the gravitation (possibly this the reason why the positron is shown as going to the past and the electron as going to the future).

That's all.


Thank you.

Isaías González Valdenebro
igonzalez@epm.net.co

Here's a somewhat Star-Trekky type question, about Alcubierre drives.

The way I understand that an Alcubierre drive works is that it warps space in such a way that the space in front of it is contracted, while the space behind it is expanded. Rather than have the ship move at all, all that happens is the space in front is contracted and the space behind expanded essentially until the ship is now "where" it wants to be.

Now, the problem I have with this is best illustrated by a sort of analogy in 1-D to make it simpler. Imagine that space is very long, stretched out rubber band, and that your ship is a dot or ant or whatever on that rubber band. The alcubierre works by sort of pinching the rubber band where the dot is and moving it closer to the destination, so that the portion of the band behind it is expanded and the portion in front is contracted. There's a problem here, however: the rubber band is no longer in equilibrium - you have to maintain a constant force just to keep it where it is. In the same sense, space isn't permanently warped by a gravitational field - that field must be continuously present in order for that space to remain warped. So what happens when you turn the drive off - you remove the force keeping the dot where it is? The rubber band will jerk back to how it was initially, the dot on it will snap back to its initial position, and the ship should be sent flying back to Earth, should it not?

The other problem with the Alcubierre drive is that it requires matter of negative mass, which does not appear to exist. Presumably, the exotic matter is what is used to expand the space behind the ship. But what if you approach the problem differently? What if, instead of letting you be pulled through space merely by its warping, you locally warped space by contracting the space in the volume immediately surrounding your ship, and actually travelled through it? The warping should move along with your ship, so space would return to normal behind you, but since you're moving through contracted space, you would cover many times more distance than you actually travelled - if the space immediately surrounding your ship was contracted by a factor of 10, for example, you would arrive at your destination in one tenth the time it would take without the drive.

So why is it that concept of the alcubierre drive works by contracting and expanding, which not only appears to not work, but also requires exotic matter, when it seems like it could work fine by just contracting space, and without that exotic matter?

Hi Dr Krauss,

Two questions actually:

If the most successfull theory (quantum mechanics) is incompatible with our concept of gravity, doesn't this mean that our concept of gravity must therefore be wrong (or worse, the other way around)?
Another way of gravity failing to conform to theory is the concept of dark matter, could you explain to people who think that dark matter is just a breakdown of how our theories describe gravity, why we should expect direct evidence of the existence of dark matter?

Cheers.

Dr. Krauss,

Are you a heliochromologist? Would you like to be a heliochromologist? It is a new field and I am encouraging only the most colorful to enter.

[Just figured he needed a break as levity is the soul of wit, roughly, and he already has the wit. ]

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Lighten up! This is a stellar board!

Dr. Krauss,

How has the scientific community embraced Mike Griffins Heavy Lift mandate for VSE? You must know that if we are to explore Europa, have space based solar power, etc.--that we are going to have to go beyond the Delta II rocket, preferably shuttle derived Heavy Lift--seeing that there is no atmosphere to aerobrake.

How could heavy-lift advocates like myself hope to change the opinions of scientists spoiled by Goldin giving them a Delta II right and left, when we have spent too little on launch vehicle development outside of EELVs no better than the Titans they replace?

Dear Dr. Krauss,
I have a question about the dimensions of string theory.
generally I heard people were talking about extra spatial dimensions only. my speculation is why there is only one dimension for time. whether it is possible to time to manifest in multi dimensions as like space?
relativity theory states that space & time are interconnected into space-time. so, is there any possibility to convert a spatial dimension into a time dimension or viseversa?