Big Bang or Cosmic Crunch?

BrianGa writes: "Yahoo news is reporting on Princeton University physicist Paul Steinhardt suggesting that the universe never began and will never end, driven forever to expand in a series of monster explosions and contract every eon or so in a cosmic crunch. This is directly contradictory to the big-bang theory. The model of the universe envisioned by Steinhardt sees the big bang as merely a turning point on an infinite road."

Comments

Read about this in the Elegant Universe....

[anthony_dipierro]

Here's a summary. I don't have the book any more so I can't quote, but notice in the summary of chapter 10 where the summary reads "When shrinkage to below the Planck length is attempted, the crunch becomes a bounce."

First of all

[dalutong]

I've believed exactly this for quite some time now.

Secondly, this doesn't go directly against the big bang theory. the big bang created _this_ universe, yes, but before it were an infinite amount of "big bangs" and "big crunches."

doesn't conflict, just tells the whole story.

black holes aren't cosmic garbage disposals

[Takeel]

If the universe stretches out infinitely in all directions, is of a density similar to here everywhere, and somehow replenishes matter lost to black holes and ..stuff.. by a mechanism that we don't understand yet,

...aaaand, stop right there.

Matter isn't lost when it goes into a black hole; it ends up in the black hole's singularity, an infinitely dense point of matter in the center.

Black holes are also thought to "leak" material in the singularity back out over time.

Re:Infinity is a very difficult concept to even..

[CTachyon]

(Disclaimer: IANAP, although I'm enamoured with the topic.)

Humans are starting to think of the universe in wrong ways. My main beef is with time. People think of time as a physical dimension that is effected by matter.... this, is only partially true.

They have sent up jets with atomic clocks to test einsteins theory of gravitation effecting time, and they think of it to be correct. The more gravity, the slower time moves. But is it really making a change to some 4th dimension, or just the speed at which the subatomic particles within matter move? ....the latter is certianly acceptable. Since matter slows down, then "time" relative to that slowed matter would infact slow....

It's not just subatomic particles that slow down, which is Einstein's true stroke of brilliance. Einstein began down the road of Special Relativity by postulating that Newton's Principle of Relativity -- no matter where you are in the universe, the laws of physics are the same for all inertial (constant velocity) frames -- is correct. One of the laws of physics, courtesy of Maxwell's Equations, requires that the speed of light in a vacuum, c, is a constant. So, if both of these postulates are correct, then everyone will agree on the value of c in all inertial frames.

This deserves some illustration. Suppose you're on a hypothetical train traveling at a constant velocity of 0.5c towards a friend, and you point a flashlight straight forward and turn it on. You perceive the beam of light as traveling toward your friend at speed c; however, your friend sees the beam of light as traveling toward him at speed c, and not speed 1.5c. How can this be?

The answer that Einstein came up with, and the only known set of physical laws of motion that is consistent with both Maxwell's Equations and the Principle of Relativity, requires that your friend sees you as flowing through time at a slowed rate, whereas you see him as the one who is slowed down. With some extra geometry not far beyond a high school math student, it's not hard to prove that the length of (you|your friend) must contract; also, some modifications to Newton's Laws are required in order to make the laws of inertia and momentum self-consistent, making (you|your friend) appear to have more mass.

It is an inescapable conclusion of Special Relativity that the actual flow of time slows down -- General Relativity, the theory which tied SR and gravity together while introducing time as a 4th dimension, is not even required to prove this result. The very CRT that you're using to view this article right now could not possibly exist if Maxwell's Equations were grossly wrong, meaning the only way to prove SR grossly wrong about the flow of time would be to disprove the Principle of Relativity -- by demonstrating that the laws of physics vary depending on where you are in the Universe!

Re:Infinity is a very difficult concept to even..

[CTachyon]

no matter where you are in the universe, the laws of physics are the same for all inertial (constant velocity) frames

Are you saying that light will always be moving at c ?? Just because light enteres a medium, doesn't mean that time slows down because light is slowing down. The reason light slows down is because it has to exite every atom that it encounteres, then be thrown out again.

That's why I mentioned that c is the speed of light in a vacuum. The speed of light in a non-vacuum medium is slowed down, to c divided by the refractive index of the medium (1.33 for water, for instance). Basic optics, known well before Einstein's time.

They've even collected good evidence that the speed of light has changed over time... I'm really starting to doubt einstein.

Citations, please?

Suppose you're on a hypothetical train traveling at a constant velocity of 0.5c towards a friend, and you point a flashlight straight forward and turn it on. You perceive the beam of light as traveling toward your friend at speed c; however, your friend sees the beam of light as traveling toward him at speed c, and not speed 1.5c. How can this be?

Take a jet for example. Say it it traveling at mach 2, and it fires a missle in which the missile maximum speed is mach 5. Now there is a stationary SAM site on the ground that will be blown up in a little bit... but the SAM site sees the missle coming at him at mach 5, and not mach 7. How can this be? Because you're missing the obvious....

I'm not the one missing the obvious. Unfortunately, Slashdot won't let me draw some ASCII art to explain, but I'll try and describe it in terms that you'll understand... remember that airspeed is speed relative to the air, and that air is essentially stationary compared to the ground when you're talking about Mach speeds.

From the perspective of the SAM site, the plane is moving at speed Mach 2 angle 0 with respect to the ground, then launches a missle that quickly assumes a path in which it is traveling at speed Mach 5 angle 315, which happens to be perfectly aimed such that it will impact the SAM site.

From the perspective of the plane, the SAM site is zooming underneath at speed Mach 2 angle 180. It launches the missle (let's presume it's guided), then observes as the missle fires up and assumes a path of travel with speed Mach 3.57 angle 293.5. The missle looks like it will fall short, except that the SAM site rushes underneath the missle just in time to be hit. Stupid SAM site!

In the train example, we have a train traveling at speed 0.5c angle 0. You are standing on the train, and your friend is directly in front of the train by a safe enough distance that he'll be able to sidestep the train when it gets close. So, from your perspective, your friend is rushing toward you at speed 0.5c angle 180, and the beam of light is rushing away from you at speed c angle 0. What does your friend see? According to Newton's mechanics, he should see you rushing toward him at speed 0.5c angle 0, and the beam of light should be traveling at speed 1.5c angle 0 (simple trigonometry -- you add two vectors with the same angle by adding their magnitudes). In reality, as confirmed by countless experiments, the most famous of which are known as as the Michelson-Morley experiments, your friend perceives the beam of light as traveling at precisely c. If you fire a railgun from the train with a slug that travels at speed 0.5c angle 0 relative to you, then your friend will see the slug traveling toward him at speed 0.8c angle 0. These results have been confirmed by many, many experiments, so the burden of proof is on Einstein's doubters to show -- using repeatable and accurate experimental methods -- that an alternative explanation can exist. The physics department at the University of California at Riverside has an excellent site introducing physics, including these two pages that explain why the ether theory from the late 19th and early 20th centuries is thoroughly debunked and cannot be modified to fit the facts without becoming an unfalsifiable hypothesis (i.e. a matter of faith).

Light does have it's speed limit. The easiest explanation for that would be a drag in the ether that keeps it from exceeding that speed.

Again, see the above links for an explanation of why ether theory cannot be falsified if it is modified to be consistent with our existing knowledge.

You perceive the beam of light as traveling toward your friend at speed c

That is the mistake in the example... It is trying to prove relativity, but without relativity, that sentence would be false... You can't prove something by initially assuming that it is true; using the theory within the explanation for the theory.

The statement assumes that relativity is true, but it's a testable and falsifiable statement that, if it were false, should be trivial to debunk. Despite multitudes of measurements and experiments, especially by the people who passionately desired to show it to be false, that very statement has not been found untrue even once.

Didn't Einstein fail math?

Yes and no. He understood math quite well, but due to dyslexia he couldn't deal very well with the rote memorization and mechanized learning required of him by the school system. He eventually learned to deal with it well enough to get excellent grades.