MigL

Really ?

Alternate timeline or not, who came up with the original idea of the time machine ?

Causality violations cannot always be explaned away by 'alternate timelines'.

Say you lived in the year 2112 and you found, in your attic, the schematics for building a time machine drawn up by your great grand-father. So you build it and go back in time to our present, 2012, and discuss the idea of the time machine and its function with your great grand-father, who after you leave and return to 2112, draws up the schematics.

Who actually came up with the idea, or was the information just created ( I love these paradoxes ) ??

But seriously...

Say you and Kip Thorne have two wormhole generators and use thrm to estabilish a wormhole with the one opening at your end and the other in Kip Thorne's office. You then take your wormhole generator, hop aboard your spaceship and blast off to Proxima Centauri at an appreciable fraction of the speed of light, all the while conversing with Kip Thorne through your end of the wormhole. You descibe the sights to him and turn around and come back to Earth, still talking to Kip Thorne through the wormhole. Upon landing on Earth you find that although only acouple of years have passed for you, the Earth you have returned to has advanced thousands of years into the future and everyone you knew is long dead. 'No problem' says Kip thorne through the wormhole, 'Just step through the wormhole and return to the present'. So you do and have just travelled thousands of years into the past.

This is an example of a macroscopic closed time-like loop, and it involves way too many unproveable assumptions and unacheivable effects ( macroscopic wormholes ??? ) for my liking. But it hasn't stopped Kip Thorne ( physicist ) from exploring the possibility. Look him up, he has done some very interesting work with so called 'time travel'.

Yet negative pressure could drive expansion, and at the very least is postulated by Guth to have driven inflation. If the universal vacuum energy 'hung up' at a false ( higher than ) zero level just after the big bang, it would have experienced violent inflation while it slowly fell to the actual zero point vacuum energy. If it never actually reached the zero point, but just drastically slowed down its descent ( much lower slope ), then it could still be driving expansion at a much reduced rate, ie. accounts for the cosmological constant.

But I guess that unless we can get a handle on a realistic value for the vacuum energy, all this is just speculation,

Yes, chapter 7 of Hawking's 'A Brief History Of Time' has a reasonable if simplistic explanation of Black hole entropy>temperature>radiation. The book is available everywhere, even used or as a download.

I don't remember since its been a long time since I read it, but does Hawking's A Brief History Of Time include a simple explanation of Hawking radiation and its relationship to energy conservation and virtual particle behaviour near the event horizon of a black hole ?

It may be enlightening reading, questionposer.

Virtual particles don't carry motion, whatever that means.

All force carrier bosons in quantum field theory are virtual particles, not all virtual particles are force carrier bosons.

Think of virtual particles as surrounding real particles such that they must be included in any calculation of mass, charge, etc. A real world analog would be a baseball moving through a viscous fluid like air, to calculate forces on the baseball you have to include contributions from the boundary layer or entrained air.

Black holes, at least outside the event horizon, are no different than any other gravitating body. They 'attract' other mass/energy.

Some advice questionposer...

I'm sure Dr Rocket doesn't need me to toot his horn, but he's not 95% classical mechanics ( maybe you mean General Relativity ). As a matter of fact his understanding of Quantum Mechanics is probably better than 95% of us on this forum. I have dealt with him for a couple of yrs and have nothing but respect for him. He can be abrasive at times, but is always insightful and steers you in the right direction. I have learned a lot from him.

There is no clear demarcation between classical and quantum physics. Some classical concepts apply to the very small and some quantum concepts apply to the very large ( you yourself alluded to the evaporation of black holes via hawking radiation, but there was considerable confusion in your argument). Some understanding of the basics is required to know which can be applied and which cannot. Do not catagorically state that since a concept is classical in nature, it is osolete and no longer viable. "Reading a book" might give you a deeper understanding of the basics.

But we don't measure to a dimensionless point...

There is a limit to accuracy we can acheive, and it is fairly 'smeared out'.

Also as Widdekind has explaned, put an EM wave through a double slit. Do you measure a point ???

Wish I had more time, gotta run.

Re-read the whole discussion.

It seems you are confused about what happens when a measurement is made on a Quantum Mechanical system.

By your misunderstanding, the collapse of the wavefunction when an observation is made, implies that the wave nature of the system becomes an actual point particle.

That is NOT the way it works. Wave function collapse is an 'interpretation' to allow for the multitudes of possibilities represented by the wavefunction and the single observed result.

The wavefunction does not collapse to a particle, and time certainly does not stop.

I didn't say there cannot be a frame where something is at rest, just that all frames are equally viable, None is preferred or universal. But you are right QM and GR operate in different domains with little overlap.

Also what do you mean by measurement of a point? According to Quantum theory we don't actually make any measurements below a certain limit because of the large energies involved. And the calculus is a differential analisys where subsequent information (position, momentum, etc. ) is derived from previous values. The continuity is inplied, not proven, as noone knows what happens at or below the Planck length.

Also keep in mind the difficulties that arise from considering particles as points. Renormalisability is, as far as I'm concerned, still just a trick ( others here may disagree ) and seems to become increasingly difficult with higher spin values ( 1/2 being easiest, 2 is impossible ). A finite size of particle seems to alleviate this problem and is one reason driving string theory.

Your first and biggest mistake, questionposer, is that since nothing is at rest ( ie the rock you pick up isn't moving in your hand but it is moving along with the earth )hat there must be a fame where it is 'actually' at rest. But as AJB has stated,"With respect to what?'. The frame you postulate would be a preferred universal frame, and unfortunately GR doesn't allow for abslute space and preferred universal frames .

Keeping in mind that electomagnetic radiation ( The only one that could possibly be generated by a human brain ) falls off in intensity with the square of the distance, the energy density required for appreciably distant telepathy, or even lightweight telekinesis, would certainly fry the sender's brain.

By all means take DrR's advice, He'll seldom , if ever, steer you wrong, but...

The expansion of the universe can simply be explaned as a global phenomena whereas locally, the expansion can be mitigated or even reversed ( attraction ) by other forces. So even though we can observe universal expansion, the Andromeda galaxy is moving towards our galaxy because gravitational force overcomes the expansion locally. We also don't get larger and our molecules and atoms don't move farther apart because the electomagnetic force overcomes the expansion. And the constituents of the atoms themselves don't expand because the strong force keeps nucleons from expanding.

In effect what you were stating about yardsticks ( even if a little confused as mentioned by DrR ) doesn't apply here. Our 'yardsticks' are not expanding so we CAN measure universal expansion.

I see what you are getting at Widdekind. The initial conditions of the quark-gluon plasma ( obviously shortly after t=0 ) constrained the quarks to be for-ever-after bound, and that is their state even today and in the future ( assuming no big crunch ).

Your argument that if initial conditions were not hi-energy/density then quarks may not be bound as they are, unfortunately cannot be proven. Still its an interesting hypothesis.

Sheldon Cooper, and if you don't know who he is, you don't watch enough TV.

But Freeman Dyson has a really cool name.

And other than Sir Isaac Newton and Enrico Fermi, I cannot think of any other current or past physicists who excel at both the theoretical and experimental aspects of physics.

Its my understanding that the Higgs mechanism is one possible scenario for the symmetry breaking of the electroweak. There are others. I think AJB has alluded to other theories.

Are you sure there is a possibility of moving a laser dot faster than c ( angularily of course )? Would that not imply a superluminal transfer of information, which is,of course, forbidden?

Edit:

Sorry AJB, not thinking clearly this morning. Of course any modulation of the laser still must travel at c, just the position may be moved angularly at superluminal speed. So no actual violatuon of relativity.

The only particles I know of that are their own antiparticles are both bosons. One is the previously mentioned photon, the other is the Z particle which carries ( along with +/-W particles ) the weak interaction. Being bosons they follow bose-einstein statistics and don't abide by the exclusion principle, they can bunch-up and have overlapping states.

You've lost me AJB ( you gotta remember to dumb it down for us ) as I don't see what the fact that 'any combination or product of solutions is also a solution' has to do with it. Am I missing something ?

Also, why is a wave function not technically a wave ? It looks like a wave and can be expanded mathematically as a combination of waves. Do you mean its not a real actual wave or am I again missing something ?

At that time, just after the big bang, there was also sufficient energy to keep quarks from pairing up.

As has been explaned, quark separation energy is finite and much lower than Planck scale energy

( in other words I don't know its exact value but I'm sure you could look it up, if interested ).

Uncharged particles also have antiparticles, and some are their own antiparticles !?!?

Yes, the two original quarks separate. The energy creates a new partner for each of the original two bound quarks. I'm not sure if you can tell, however, as you cannot label the quarks. You may be able to tell from conservation of momentum considerations.

Well, let's see if i can give some examples, questionposer.

Consider the wave equation of an electron. Now a classical wave would be like a bucket with some water in it, if you agitate the water, waves spread out until they hit the siges of the bucket and are reflected.

The electron,o on the other hand, can do something that classical particles and waves cannot. It can 'tunnel' to the outside of a square potential well, and back in again, if it chooses to. We explain this by having the wave overlap the sides of the potential well so that part of it lies outside the well. Now it doesn't make sense to consider that outside part of the wave to be 'part' of an electron since we consider electrons fundamental point particles, and so indivisible. The only available choice is to relate the wave equation to a a probability.

A similiar situation arises in electron scattering off an obstacle. In this case the incident electron wave would produce, upon scattering, several larger ripples or wavelets. Again we cannot conclude that these ripples represent pieces of a broken-apart electron for the same reasons presented in the first example. Again we must conclude that these ripples are related to the differing probability of the incident electron being deflected in that direction.

I realise that the wave function and Shroedinger's equation are not the same, AJB, butit was overlooked for the sake of simplicity.

I wold go so far as to say there is no such thing as information conservation, yet. It is a quantum mechanical concept being applied to the 'classical' theory of GR. Only a quantum gravity theory will provide answers.

Yes, you definitely should learn the math, it really isn't that difficult.

But you should be less concerned with why they are waves, a common state of many physical phenomena, and more concerned with 'what' is waving. Most waves we are familiar with are in a medium such as water, air,etc,or waves of something physical such as electric and magnetic fields. What is waving in Shroedinger's equation however is not really a physical wave, but is somewhat related to a probability wave since the square of the amplitude of the wave at any point, is the probability of finding the particle at that point.

So as you can see it isn't the math, its the concepts of QM which are difficult to wrap your head around.