Technology Is Time Travel (going backwards) Possible? - Page 18




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  1. #171
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    Quote Originally Posted by KarinsDad View Post
    Actually from what I've read, MOND makes very good predictions in many areas (and not just galaxy speed), not so good ones in others. To focus on just those where it falters and say that it is probably wrong because of those isn't objective science. No doubt, MOND is minimally incomplete and even possibly incorrect because it cannot explain everything. Dark Matter also has areas where it does not make good predictions (or at least consistent predictions from one galaxy to the next).
    I want to come back to this again briefly. From studying the CMB, we know that there must be some kind of non-normal dark matter in essentially the right amount to explain the speeds of galaxies in clusters, rotation of stars in galaxies, etc. Even some strong MOND advocates agree. Is it possible that MOND is necessary to explain the motions of, for example, stars in galaxies? Yes. I haven't heard anyone to argue that it's not possible (that is, another physicist make this case). However, it seems reasonable to most people that dark matter works well with what data we have, so there is no reason yet to add a new ingredient of MOND until we see something that dark matter predicts incorrectly.

    There are a lot of recent articles that are starting to support MOND more and more, but some of the more (apparently, who can actually tell) objective sources that I've recently read seem to indicate that it is not winning the fight quite yet. And, this is how you appear to view it.
    I'm not sure about "a lot" of recent articles, at least not scientific research. The vast majority is really on dark matter. Think of it like a company. You might spend some of your capital on a risky but high-payoff kind of project (MOND), but you want to invest almost all of it on a less risky but also pretty high-payoff project (DM). I should also mention that there are strong motivations to believe that there is particle physics beyond the Standard Model of particle physics (for reasons independent of wanting dark matter) which themselves often include possible dark matter particles.

    But, I wouldn't be surprised if the final answer is a combination of a few current theories. The gravitational equations might be wrong and there might be invisible matter out there. There also might be other forces at work beyond just gravity or gravity might not work exactly as thought.

    http://blogs.scientificamerican.com/...el-of-reality/
    It's possible. There are people following up on the papers discussed in this blog post. But some of the history not mentioned in that post is that Verlinde's idea is very similar to work done a long time ago (10-20 years, I think) and has never produced much. Could it be right? Yes, but it just doesn't have a good track record yet. The logic in the papers also seems a bit circular in places, if I recall.

    But, when someone like Physics Nobel Prize winner Martinus Veltman (who helped architect the standard model of particle physics) states that he doubts that Dark Matter exists at all, other scientists should at least listen:

    http://www.scientificamerican.com/ar...au-dark-energy

    He might be wrong. Only time and a lot of hard work will tell.
    I'm listening to the clip. And people do respect that (listen to the woman talking to the other students at around 11:30). But I can tell you that he makes some inaccurate statements (in particular, saying that we believe in dark energy because of one experiment -- it was a number of things together that convinced people).


    An absence of data in the case of Neptune? Actually, this analysis is a bit flawed.

    Scientists did have data. They knew the distance from the Sun to Neptune. They had an idea of its mass and chemical composition. They had information on the amount of solar wind that arrived at Earth and models to predict how much would arrive at the other planets. They did have some information on wind speed on other gas giants in the solar system like Jupiter and Saturn and had even more wind speed data once Voyager 1 and 2 got to Jupiter and Saturn, a decade before Voyager 2 got to Neptune.

    To insinuate that scientists had no data and then "Wow, now we have data" is incorrect. They had quite a bit of data there. Their theories and models were just incorrect based on the data that they had at the time. But, there wasn't a total lack of data there.
    OK, I think maybe I wasn't entirely clear in what I was saying. They did not have direct data on the wind speeds at Neptune. What you're saying is that they had a lot of indirect information to build a model of Neptune's climate -- true -- but that model turned out to be incorrect. (By the way, solar wind is not the same as a planetary wind.)

    This is very different than the case of dark matter. First off, the idea of dark matter was prompted by data (stellar motion in galaxies). It wasn't a case of thinking about something we already saw (Neptune) and trying to model something we hadn't directly observed yet (the winds). Then, people started asking about predictions or consequences of the idea of dark matter. And these predictions have been verified, in at least one case (the CMB) very very well.




    If one does a matrix diagram of Dark Matter theories and Gravity Modification theories, one finds that both types of theories cover some observations very well and other observations, not so well.

    The problem that has been creeping more and more into at least the literature (and opinions like Martinus Veltman's) is a) DM has its flaws just like MOND or other theories, but more importantly b) DM just hasn't been found yet. Period. Not even a hint of it. At least to the lay person, DM sounds like magic. We don't know what it is, we've spent many hundreds of thousands of manhours of some of the brightest people on the planet, and many millions of dollars trying to figure out what it is and/or detect it, but we are teaching our students that it must be true because the equations tell us that it is true.

    Well, of course one is going to have thousands of scientists the world over that believe it is true if that is what they were taught in school and there is no alternative theory that explains it all better. Just look at how quickly the students in the video above were ready to defend DM. Why? Because that is what they were taught as true science. They know about alternative theories, but they discard them out of hand without putting any real work into them.
    You have more than one point here, and I'm going to address them out of order. Last one first: I think it's really quite unfair to the astrophysics/cosmology/particle physics community to say that it "discards" alternative theories because of "what they were taught as true science." First of all, there are definitely people working on alternatives, like MOND, and the division of labor is the result of an optimization process: each physicist deciding (1) what seems like a promising avenue based on current evidence and (2) where he or she can make a good contribution. Next, science has proven to be very good at self-correction. As you've cited, there are "contrarian" scientists, and people do listen when the give solid arguments. (Veltman's in that video were not well-articulated IMO, but maybe he has stronger reasons than what came out in the clip.)

    Back to the first point. I hope I've made it clear that the most important, cleanest observation, the CMB, points strongly to the existence of matter outside the Standard Model. It's also pretty difficult for theories without dark matter to explain things like the Bullet Cluster.

    And now, the grand finale . Why haven't we discovered DM in a lab yet? After all, there are lots of experiments looking for it as it passes through earth. Well, first off, there are some experiments that claim to have detected it (though there is a lot of scepticism about those results for various reasons). But even leaving that aside, should we expect to have discovered DM in those experiments? Certainly, the models studied the most should be in range of detection, at least. But why are they the most studied? At least partly because people wanted to be ready in case they were detected! Remember, all cosmology tells us is that there's some kind of non-luminous nearly pressureless type of matter not in the Standard Model. The only way it absolutely has to interact with normal matter -- like our experiments -- is through gravity. If that's it, our experiments can't possibly detect dark matter passing through the earth. And I might add that there are some good possibilities for dark matter in well-motivated extensions of the Standard Model that would not be detectable. So this is what we'd call a model-dependent question. Yes, it would be disappointing if we can't find DM in a lab. Would it be a waste of money? Well, millions of dollars is chump change compared to some experiments, the profits of some corporations, etc. I tend to think of it as fulfilling our curiosity.

 

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    Quote Originally Posted by KarinsDad View Post
    Well, of course one is going to have thousands of scientists the world over that believe it is true if that is what they were taught in school and there is no alternative theory that explains it all better.
    I....
    I mean....


    ...there is no alternative theory that explains it all better.
    Do you want them to believe in a theory that explains it all worse?
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    Backwards would be the only theoretical way to travel. The future has endless possibilities and thus cannot be a location.

    Backwards, however, means that you have already traveled back in time, and thus cannot change anything, for it would have been changed in your life already.

    We can argue about the science all day, but in the end, the flow of time will not be changed.

    If I go back in time and kill Hitler, that means he was dead from me already, and I hadn't changed a thing.

    if I had gone back and killed me, well that raises all sorts of questions, but nevertheless, that too would already had to have happened.
    SO EIN MIST!

  • #174
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    Quote Originally Posted by Summer-Knight925 View Post
    The future has endless possibilities and thus cannot be a location.
    Why do you think so? What evidence do you have that there's actually more than one possible future?

    Hopefully you aren't under the delusion that you have something like 'free will' and would therefore be able to influence the future in any way
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    Quote Originally Posted by KarinsDad View Post
    Well, of course one is going to have thousands of scientists the world over that believe it is true if that is what they were taught in school and there is no alternative theory that explains it all better. Just look at how quickly the students in the video above were ready to defend DM. Why? Because that is what they were taught as true science. They know about alternative theories, but they discard them out of hand without putting any real work into them.
    You know how, when discussing games, we ask folks to not assign motives to others? That isn't just for game discussions. It is a general precept. An internet video or two do not stand as a good gauge of how an entire group of people think.

    Quote Originally Posted by freyar View Post
    I think it's really quite unfair to the astrophysics/cosmology/particle physics community to say that it "discards" alternative theories because of "what they were taught as true science."
    Specifically: Those reading popular reportage of science should not assume they know what's being taught to the students and grad students in the classroom, or discussed among the practitioners.

    The only way it absolutely has to interact with normal matter -- like our experiments -- is through gravity. If that's it, our experiments can't possibly detect dark matter passing through the earth.
    Well, some of the suggestions have ways to interact other than gravity. WIMPs, for example, also interact through the Weak nuclear force - and with a large enough detector, you might catch them through such interactions.

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    Quote Originally Posted by Umbran View Post
    Specifically: Those reading popular reportage of science should not assume they know what's being taught to the students and grad students in the classroom, or discussed among the practitioners.
    There are lots of online video classroom lectures and other presentations on the Internet these days. Obviously, nobody is up to speed on everything being discussed, but then again, it's not a complete vacuum either.

    Quote Originally Posted by Umbran View Post
    Well, some of the suggestions have ways to interact other than gravity. WIMPs, for example, also interact through the Weak nuclear force - and with a large enough detector, you might catch them through such interactions.
    Or one could catch something else and because the interaction is so weak, one could assume it was what they were looking for as opposed to what it really is. It's an extremely hard science at this point.
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    Quote Originally Posted by Jhaelen View Post
    Hopefully you aren't under the delusion that you have something like 'free will' and would therefore be able to influence the future in any way
    that's a topic for another thread I been meaning to start. Namely, why don't people like the idea of NOT having Free Will. We should let this thread finish out though. Somebody's bound to say something insightful or inciteful yet.

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    Quote Originally Posted by freyar View Post
    However, it seems reasonable to most people that dark matter works well with what data we have, so there is no reason yet to add a new ingredient of MOND until we see something that dark matter predicts incorrectly.
    How about the Cuspy Halo problem? CDM is the simplest explanation for DM, but the theoretical solutions to this problem require at least some type of an adjustment to CDM models. MOND doesn't have the Cuspy Halo problem TMK because it's a direct outcome of CDM. Pilipenko, Lukash, et al just released a new model a few months back that might solve the problem, but that doesn't mean that the problem is definitively solved yet, correct?
    The first sign of a broken rule is when someone suggests that the way to stop it is by readying an action.

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    Quote Originally Posted by KarinsDad View Post
    There are lots of online video classroom lectures and other presentations on the Internet these days. Obviously, nobody is up to speed on everything being discussed, but then again, it's not a complete vacuum either.
    But those video lectures are not representative of the experience of being a grad student in physics, or any of the hard sciences. You were questioning how actual practitioners thought, and go about their business - video lectures don't show you what and how we actually learn, or how we are taught the activity of doing science.

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    Quote Originally Posted by Umbran View Post
    But those video lectures are not representative of the experience of being a grad student in physics, or any of the hard sciences. You were questioning how actual practitioners thought, and go about their business - video lectures don't show you what and how we actually learn, or how we are taught the activity of doing science.
    No, but they are representations of what is being taught to grad students, the statement of yours which I was responding to.
    The first sign of a broken rule is when someone suggests that the way to stop it is by readying an action.

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