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  • #31
    The only problem is that string theory has holes in it big enough to drive a Mack truck through. It also currently has zero basis in reality and is best described as a mathematical exercise.

    That being said, some of the things it says are very promising. I think string theory has the potential to give us some remarkable insights into the universe, but I seriously doubt that it represents reality.[/QUOTE]

    i agree and disagree with this one. String theory doesnt really work until you add an 11th physical dimension to the calculations then alot of the holes disappear. the 5 sets of equations all balance into one coherent theory with this addition. However, M theory is not complete as of yet. labeling it m theory or hell anything you want to call it is unimportant. i believe once it is complete and we have the ability to test the theory we will have a good understanding of the universe. a complete one? no, but a good basis on which to build. it would be arrogant and dangerous to assume at our level of development that we have the ability to fully understand the universe. this could take millenia.
    "Your not gonna find a bang maid cause theres no such thing."
    "I already did...your mom....good bye.".

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    • #32
      Originally posted by Archaeopteryx lithographica View Post
      Yep. In about 100 billion years all the stars will have burnt out, all the black holes will have evaporated, and all the matter will have decayed. The universe will be cold, lifeless, black, and dead.

      Have a good night.

      Of course, that's assuming everything we know now is correct...
      i was thinking about this all night. it is a grim outcome. all of the energy in the universe will be uniformly distributed throughout the expance. but how will it interact with the different fields. they should not decay. if they are an intrinsic part of the fabric of the universe interactions of forces may continue. if interactions continue between energy and the 4 forces that would change smootheness of this final state. once it is no longer smoothe the interactions become more pronounced in the denser regions. which could begin a chain reaction and start the process all over again. all it should take is one tiny ripple.
      "Your not gonna find a bang maid cause theres no such thing."
      "I already did...your mom....good bye.".

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      • #33
        Originally posted by TommyKav View Post
        i agree and disagree with this one. String theory doesnt really work until you add an 11th physical dimension to the calculations then alot of the holes disappear. the 5 sets of equations all balance into one coherent theory with this addition. However, M theory is not complete as of yet. labeling it m theory or hell anything you want to call it is unimportant. i believe once it is complete and we have the ability to test the theory we will have a good understanding of the universe. a complete one? no, but a good basis on which to build. it would be arrogant and dangerous to assume at our level of development that we have the ability to fully understand the universe. this could take millenia.
        My point was that even with 11 dimensions, string theory still doesn't work. It's not even a theory. I like this wonderful quote from Jim Holt from The New Yorker magazine: "Yet, for all this activity, not a single new testable prediction has been made, not a single theoretical puzzle has been solved. In fact, there is no theory so far—just a set of hunches and calculations suggesting that a theory might exist." I take issue with anyone referring to string theory as "coherent." Quantum field theory is incoherent enough; string theory is WAY the hell out there.

        I think there is something to string theory and I am glad that research is being done on it, but I really wish that more energy was devoted to other areas as well.

        I might sound angry when I write about stuff like this, but that's just because I start getting terse and professional when talking about physics.

        Originally posted by TommyKav View Post
        i was thinking about this all night. it is a grim outcome. all of the energy in the universe will be uniformly distributed throughout the expance. but how will it interact with the different fields. they should not decay. if they are an intrinsic part of the fabric of the universe interactions of forces may continue. if interactions continue between energy and the 4 forces that would change smootheness of this final state. once it is no longer smoothe the interactions become more pronounced in the denser regions. which could begin a chain reaction and start the process all over again. all it should take is one tiny ripple.
        I don't understand what you're saying here.
        Ph.D., Theoretical Physics '16
        kind of a douche

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        • #34
          You mentioned black holes... So, why are black holes created? What evidence is there to support if there is another end to the black hole? Or does it seem to just go to infinity?
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          • #35
            Originally posted by marlon View Post
            You mentioned black holes... So, why are black holes created?
            Normally in a star the inward gravitational pull of all its matter is balanced out by the outward pressure caused by the intense heat produced from nuclear fusion. When a star goes supernova, it blows off its outer layers and the inner layers get SUPER compressed. In fact, they become so dense that the gravitational pull overcomes the outward pressure. When the gravitational pull of this super dense matter becomes so strong that nothing, not even light, can escape, the star has become a black hole. It is called that because it is impossible to "see" it since any light you shine on it just gets sucked in and cannot be reflected.

            Theoretically, any time you get matter past a certain density, it will create a black hole. In fact, there is a simple equation that will give the radius of the black hole as a function of its mass. This is:
            r = (2*G*M) / c^2
            Here G is just a constant (the universal gravitational constant), M is the mass, and c is the speed of light.


            Originally posted by marlon View Post
            What evidence is there to support if there is another end to the black hole? Or does it seem to just go to infinity?
            There is no evidence at all. In fact, the laws of physics don't work well once we get to the center of the black hole, because they tell us that the matter becomes INFINITELY compressed into a zero volume. As far as we can tell, there are no infinities in nature. Not only that, but having mass inside a zero volume doesn't make any sense. To know what happens at the center of a black hole, we need a quantum description of gravity that tells us what gravity does at extremely small scales.

            The mathematics of black holes do imply that there is another "end" to the black hole, where everything comes back out, called a "white hole." However, as far as we can tell this just seems to be a mathematical curiosity; a relic of an imperfect description of nature. That doesn't rule out its existence, but we haven't seen anything like that in the universe.
            Ph.D., Theoretical Physics '16
            kind of a douche

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            • #36
              Something I was thinking about while carrying fishing nets through a major metropolitan hospital:

              Maxwell's Equations are a set of 4 vector equations that completely describe all classical electromagnetic phenomena. They are mathematically elegant, beautiful, and symmetric. And they're wrong.

              Einstein's general theory of relativity completely describes how gravity works by warping spacetime. It too it elegant, powerful, and tells us about the fate of the universe. And it's wrong.

              Quantum field theory (which results from the union of quantum mechanics with special relativity) is the most successful physical theory ever produced. It has given results accurate to the 26th decimal place. And it's wrong.

              Notice a pattern here? Everything that physics produces is, at best, a model. We can only build models that describe what we see in the universe. Maxwell's equations tell us how light reflects off surfaces and why the sky is blue, but it fails miserably when we look at extremely small scales. General relativity can describe the motion of planets, galaxies, and the universe as a whole, but it gives nonsensical garbage when we apply it to quantum theory. Quantum field theory describes how atoms work and how the sun shines. But it tells us the neutrino should not have mass (it does), and if we try to combine it with gravity it gives garbage answers.

              Physics is all about trying to describe the universe the best we can. How can we know if it's every correct? I don't think we can. We can only try the best we can, find problems with our model, and try to fix them.
              Ph.D., Theoretical Physics '16
              kind of a douche

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              • #37
                Dino - what are your thought on the possibility of Einstein-Rosen bridges existing?
                "Your not gonna find a bang maid cause theres no such thing."
                "I already did...your mom....good bye.".

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                • #38
                  Originally posted by TommyKav View Post
                  Dino - what are your thought on the possibility of Einstein-Rosen bridges existing?
                  I think they are fascinating and definitely worth researching, but I sincerely doubt their existence. My intuition tells me that they are a relic of our incomplete understanding of the universe. Of course, if wormholes DO exist, that would fucking ROCK.
                  Ph.D., Theoretical Physics '16
                  kind of a douche

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                  • #39
                    Time travel... what are the possibilities? best theories?
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                    • #40
                      Originally posted by Archaeopteryx lithographica View Post
                      .....while carrying fishing nets through a major metropolitan hospital:
                      ....
                      why? what were you fishing for there?
                      -KidRok-
                      "....because I won't accept that I can't."


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                      • #41
                        Originally posted by KidRok View Post
                        why? what were you fishing for there?
                        Medical students. Unfortunately all the ones here seem to be really stuck-up and snooty. I'm not sure what it is about Vanderbilt that attracts that kind of person.

                        Originally posted by marlon View Post
                        Time travel... what are the possibilities? best theories?
                        By "time travel" I assume you are referring to traveling back in time. Anybody can build a time machine to travel into the future. In fact, just the other day I built a time machine. I got inside a cardboard box, waited 5 minutes, and POOF! I traveled 5 minutes into the future!

                        Theoretically time travel into the past may be possible, but I think that is only due to our very primitive understanding of the way the world works. I will give you two scenarios. One will give a compelling reason why you probably cannot travel back in time, and the other is a theoretical way to construct one that also gives limits on how far back in time you can go.

                        Let's imagine for a minute that we can build a time machine and that we do build one. Let's say we travel back in time to when our father was a child. We meet him, say "Hi," then shoot him in the face with a shotgun and kill him.

                        This leads us to a paradox. If we kill our father, then we could never have been born to eventually travel back in time and kill him. But if we were never born and thus never went back in time to kill him, then he lived. But if he lived, then he gave birth to us, and we eventually go back and kill him. So being able to build a time machine for travel into the past creates causal paradoxes that we don't really know how to resolve. Sure you can come up with weird explanations like science-fiction stories use, like alternate universes and such. But as far as we know the universe doesn't like weird paradoxes like the one above.

                        Now in theory, we can build a time machine to travel into the past. However it only allows travel back to the point when the time machine was created. To see how that works, we first need to learn a bit about the thing Tommy mentioned a second ago, called a "wormhole." A wormhole is essentially a short-cut through spacetime that allows us to bypass the normal travel route. This allows us to essentially travel faster than light. Now special relativity tells us that nothing can travel faster than light... in a fair race. If we ran alongside a light ray along a winding obstacle course, the light ray would always win. But we could win if we took a shortcut through a tunnel that ran in a straight line under the obstacle course. For a good picture illustrating how a wormhole works, look at this picture from the Wikipedia entry for "wormhole": http://en.wikipedia.org/wiki/File:Worm3.jpg

                        The next thing we need to know about in order to build a time machine is a law from special relativity. It is kind of weird when you first learn about it, but the neat thing is that it has been verified experimentally. The law is this: Time passes more slowly for moving observers. To demonstrate this a bit, let's say we have two astronauts in outer space, floating side-by-side, with identical clocks. They synchronize their clocks so that they read the same time and pass at the exact same rate. Now one of the astronauts turns on his rockets and flies away from the other astronaut at 90% of the speed of light. Every time the moving astronaut sees his watch move forward by one second, he shines a beam of light back at the stationary astronaut. Now the stationary astronaut sees these beams of light flashing at him from the moving astronaut. By timing these flashes of light and comparing them to his own clock, the stationary astronaut can see how time is passing for the moving astronaut. We won’t show the mathematics of it, but it turns out that the stationary astronaut will see that the flashes of light come more slowly than seconds are passing on his own clock. This means that time is passing more slowly for the moving astronaut than for the stationary one. Again, this slow-down of time for a moving observer has been experimentally verified many times, so we are pretty certain that it is a universal reality.

                        Now that we know a little about wormholes and relativistic time slowdown, we can put the two together to make a theoretical time machine. Now to do this, we will make several assumptions. 1) We can create a wormhole that is stable and allows us to travel safely through it. 2) We can move each opening of the wormhole as much as we want to. Now let’s imagine we create a wormhole. One end of it is on Earth, in our lab. The other end we create in a spaceship that is orbiting Earth. Now as we said before, the wormhole is big enough to step through, so we can do that at any time. The pilot of the spaceship starts flying away from Earth at almost the speed of light. The spaceship flies for 5 years away from Earth, then turns around and flies back for 5 years, returning to its starting point after a total of 10 years.

                        However, due to the relativistic time slowdown, while 10 years have passed on the spaceship, 20 years will have passed on Earth. Now if we put the 2 end of the wormhole right next to each other, a person who walks through it can travel back in time by 10 years! Depending on how we make the spaceship fly, we can change the amount of time you can go back. But we are forever limited how far we can go back, because the earliest time we can go back to is the time when we created the wormhole. Thus for this theoretical time machine, you can only go back in time to when you first created it.

                        Now can a wormhole exist and be stable? Probably not. Do we have the technology to make one? No way. We can’t even build a spaceship that can fly fast enough for the relativistic time effects to be significant. Personally I don’t even thing wormholes can exist in our universe, but it sure is fun to think about.
                        Ph.D., Theoretical Physics '16
                        kind of a douche

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                        • #42
                          Thanks for taking the time answering my question Dino-bird. You do an incredible job dumbing it down for the regular people lol.

                          If time moves more slowly for a moving object, does that mean theoretically if I moved at the right speed in space for long enough, I can come back 50 years from now and not have aged say more than a day?

                          How would a theoretical wormhole be created?
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                          • #43
                            Originally posted by marlon View Post
                            Thanks for taking the time answering my question Dino-bird. You do an incredible job dumbing it down for the regular people lol.

                            If time moves more slowly for a moving object, does that mean theoretically if I moved at the right speed in space for long enough, I can come back 50 years from now and not have aged say more than a day?

                            How would a theoretical wormhole be created?
                            for the first part yes. if you could travel fast enough time for you would slow down enough to accomplish this.

                            to crerate a traversable wormhole something verry special is needed called exotic matter. exotic matter exerts a force opposite to gravity. the problem with wormholes that you can travel through is that almost as soon as you created it it would collapse so fast that you wouldn't even be able to get a beam of light to the other side. it is theorized that some kind of exotic matter would be needed to keep the throat of the wormhole open. so far exotic matter has not been discovered.
                            "Your not gonna find a bang maid cause theres no such thing."
                            "I already did...your mom....good bye.".

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                            • #44
                              Originally posted by marlon View Post
                              Thanks for taking the time answering my question Dino-bird. You do an incredible job dumbing it down for the regular people lol.

                              If time moves more slowly for a moving object, does that mean theoretically if I moved at the right speed in space for long enough, I can come back 50 years from now and not have aged say more than a day?

                              How would a theoretical wormhole be created?
                              if I get the time later today I will show you the calculation to find out how fast you would have to go to make that particular time difference happen.

                              To (not) answer your second question: To the best of my knowledge, no one currently knows how to create a wormhole where none already existed. I've never seen any ideas on how this could be done. Of course, I'm not up-to-date on the latest research in the field, so there may be an idea with which I am unfamiliar.
                              Ph.D., Theoretical Physics '16
                              kind of a douche

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                              • #45
                                Originally posted by Archaeopteryx lithographica View Post
                                if I get the time later today I will show you the calculation to find out how fast you would have to go to make that particular time difference happen.

                                To (not) answer your second question: To the best of my knowledge, no one currently knows how to create a wormhole where none already existed. I've never seen any ideas on how this could be done. Of course, I'm not up-to-date on the latest research in the field, so there may be an idea with which I am unfamiliar.
                                i took look around about creating a wormhole. there is a few half cocked ideas but no real solid theory or evidence that points towards one being able to be created where nature didnt do it. one idea involved increasing the rotational velocity of a large star and another doing the same with an entire solar system but again nothing more than a load of crap if you ask me.
                                "Your not gonna find a bang maid cause theres no such thing."
                                "I already did...your mom....good bye.".

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