Is Time Travel (going backwards) Possible?

[Nellisir]

How long you've been looking isn't really a measure though. Mankind was trying to fly for millennia (since Daedalus, at least), and it took the Wright Brothers to get us off the ground.

What Umbran said. Looking does not mean that you're looking in the right places, or that you have the right instruments to see what you think you're looking for. Extrasolar planets. We've been looking for decades. We know where they are. We know what they are. We know now that there are billions and billions and billions of them. But we didn't actually find one until 1992. We've been seeing planets around other stars longer than we've been able to see the accelerating expansion of space.

 

[tomBitonti]

The difficulty is that the effects of the overall expansion of the universe (whether the accelerating kind or a more mundane decelerating kind) do not just "add" with the effects of the matter in the galaxy on gravity. (We say the equations of general relativity are "nonlinear" because the results are not additive.) So, while I don't have the exact solutions to the equations at hand in this case, what you do expect to happen is that the gravitational attraction of the matter in the galaxy to "win" over the expansion of the universe, so the space inside the galaxy shouldn't stretch. In other words, the galaxy is "gravitationally bound," so the distance across the galaxy shouldn't be increased by the overall expansion of the universe. That will only affect distances between objects that aren't bound together.

Another point to make is that, even if the expansion of the universe were happening in our galaxy, it would be a very small effect. The expansion is only noticeable on very large distance scales (for example, the expansion rate between our Milky Way and Andromeda, the closest large galaxy, is quite slow).

What's interesting is when you get borderline cases, like galaxies that are gravitationally attracted to each other but also being swept apart by the expansion of the universe. Then there is a legitimate competition between the two effects.

I hope this doesn't muddy the picture, but cosmology is a big and sometimes complicated subject.

No. Remember above, with the bar magnet? Once the magnet has picked up the nail or pin, do you expect gravity to slowly, very slowly, pull the pin away anyway? No. It's there, it is stuck, and it isn't gonna move.

The forces of gravity are strong near matter. Very close to matter, space isn't expanding at all (very close to really big chunks of matter, space collapses - black holes!). As you move away from matter, though, the force of gravity decreases. Eventually, the force of gravity is small enough that it no longer counters the effective forces of the dark energy, and way out there, expansion accelerates.

In fact, the universe is mostly empty space - there's a whole lot of "force of gravity is small" out there. So, on the whole, the universe is expanding, and that expansion is accelerating. It is only near these tiny islands of galaxies where this is not true.

If I may: A photon starts a billion light years away. In the frame of an observer on the earth, is the photon already red shifted, or does the red shift occur as the photon travels to the earth? If the red shift travels while the photon travels to the earth, what is different about the photon's experience as it travels to cause it to red shift, compared, say, to a photon in a perfect resonant cavity bouncing back and forth for a billion years? Why does that photon never red shift, but the one that travels from a billion light years away does?

TomB

 

[JustinAlexander]

There is "a chance" for just about anything. There's "a chance" that Morrus is actually Elvis Presley.

I knew it!

 

[KarinsDad]

Yes. And? So what? Is there some preferable alternative?

No. Not at all.

I would just prefer to read a scientific article (and I read a lot of them, I just don't really have the background to discuss them rationally) and have the authors be a bit more circumspect about their discoveries. The tone of many articles is that what the scientists found is fact. I'd like to watch more lectures (which I also watch quite a few of) where the professors use the word hypothesis a bit more.

The reason is that the general public and even our scientific students are a bit misled into thinking that science is nearly 100% accurate in many non-bleeding edge areas and as we know, it is an evolving process where new data and experiments and observations and tools can and occassionally do, change current scientific theory.

With respect to the OP's question, I suspect that time travel is impossible. I have no proof, but to me, the burden of proof is upon those making the claim that it is. Some people say "extraordinary claims require extraordinary evidence". I don't go quite that far. I just say that "extraordinary claims require evidence". Time travel, teleporting, UFOs that contain extraterrestrials here on Earth, faster than light travel (and ghosts and bigfoot): most if not all of this probably does not exist at all except in the minds of people. Even some recent theories like superstring theory (and branes, multiverses, etc.) are probably just so much poppycock. I cannot prove that, but then again, the burden of proof is not on me. It's on the ones making the claim.

Just because mankind can think of something doesn't make it fact. Usually without some extremely solid evidence and multiple different experiments/observations to back it up, many of mankind's facts are nothing of the kind. Mankind has had a long and illustrious career of being wrong. I really wouldn't be surprised if Dark Energy and especially Dark Matter end up in the trash heap of scientific theories within this century even though they are being taught as basically fact today. We have zero scientific instruments located outside of our galaxy (and no really sophisticated ones located outside our solar system), so to claim that we understand how the macroscopic universe works (and how it started) based mostly on electromagnetic energy observations from thousands to billions of years ago is probably a bit naive. I keep going back to Neptune. When mankind can be wrong and doesn't have enough information, he probably is wrong.

One other note. A very large portion of current theory on the microscopic universe is based on particle accelerator experiments. Unfortunately, that's like determining the function of a computer inside a car based on an automobile wreck. Look at the pieces, determine what's going on. Although there is probably much validity to it, there might also be some misleading information from it that scientists pretty much regard as fact today, just based on the type of experiment it is. It will be interesting to see how different those current theories might become if we ever come up with a way to generate particles smaller than protons, electrons, etc. in order to peer more closely without colliding subatomic particles.

The nice thing about our current society is that science has made some deep strides in the last few centuries and the pace has been picking up significantly due to computers and advanced manufacturing techniques. But, don't be surprised if many of the concepts that scientists take for granted today (especially in the macroscopic and extremely small microscopic levels where our viewing windows are so limited and possibly distorted, not so much in the areas like chemistry) are drastically modified or even eliminated over the next few decades or so. I have no evidence for that, I just have mankind's track record.

 

[Morrus]

I would just prefer to read a scientific article (and I read a lot of them, I just don't really have the background to discuss them rationally) and have the authors be a bit more circumspect about their discoveries. The tone of many articles is that what the scientists found is fact. I'd like to watch more lectures (which I also watch quite a few of) where the professors use the word hypothesis a bit more.

What are you reading? Articles by journalists about science, or the actual papers? Because I don't believe there's such thing as a peer-reviewed scientific paper in existence which presents itself as fact (at least not one not by a crank of some kind); and popular science books written by scientists, in my experience, generally don't - to the point of overusing the word "hypothesis".

The reason is that the general public and even our scientific students are a bit misled into thinking that science is nearly 100% accurate in many non-bleeding edge areas and as we know, it is an evolving process where new data and experiments and observations and tools can and occassionally do, change current scientific theory.

I don't think that's the fault of researchers. That's the fault of educators and media. Researchers do research and publish papers full of math. If the public and students are getting the wrong impression as to what those papers contain, blaming "scientists" is even less factual than the very articles you're criticizing.

But there are certainly vast swathes of scientific research where it can be stated that the theories make correct predictions nearly 100% of the time; I would suggest that calling these, as you put it "nearly 100% accurate" is a perfectly reasonable turn of phrase to use.

To take a silly, simple example - there's nothing at all wrong with a schoolteacher telling their students that speed is equal to distance divided by time. That's "nearly 100% accurate" for any normal purpose. Sure, you can get all nit-picky with 12 year-olds about relativity and such, but at that point you stop educating them and start confusing them.

 

[KarinsDad]

What are you reading? Articles by journalists about science, or the actual papers? Because I don't believe there's such thing as a peer-reviewed scientific paper in existence which presents itself as fact (at least not one not by a crank of some kind); and popular science books written by scientists, in my experience, generally don't - to the point of overusing the word "hypothesis".

A lot of what I read comes from here:

http://phys.org/science-news/

Many of these articles are interviews with the scientists who write the papers. It could be journalistic bias, but then again, it happens quite a bit. I don't have the actual background to read (and understand) peer-reviewed scientific papers, just the synopses of those.

I also habitually read Scientific American.

I don't think that's the fault of researchers. That's the fault of educators and media. Researchers do research and publish papers full of math. If the public and students are getting the wrong impression as to what those papers contain, blaming "scientists" is even less factual than the very articles you're criticizing.

Agreed. Although I have read a few actual papers (mostly from grad students, not researchers in the field) where the scientific method is not rigorously followed, or assumptions are made. I tend to lump those under "I must not understand this completely because peer review should have caught this", assuming that I am the one in error.

But there are certainly vast swathes of scientific research where it can be stated that the theories make correct predictions nearly 100% of the time; I would suggest that calling these, as you put it "nearly 100% accurate" is a perfectly reasonable turn of phrase to use.

You mean like Mond Theory which is generally ignored by the scientific mainstream, but is nearly 100% spot on with regard to galaxy rotational observations? Mond puts all Dark Matter theories to shame in many areas. It's only real weakness is with regard to scales larger than a galaxy. Then again, I'm not sure if anyone has combined Mond with Dark Energy theories yet either. It could fall apart at larger scales because it doesn't take into account Dark Energy.

I'm not claiming that Mond Theory is correct, but I do think that scientists tend to be blind to theories which don't match what they've believed most of their lives.

 

[Morrus]

but I do think that scientists tend to be blind to theories which don't match what they've believed most of their lives.

That's not a very nice thing to say. Scientists are nothing like that; they're the very definition of the opposite. Scientists, in my experience, are pretty much the group most open to new things I've ever met; they're continually striving to uncover new stuff and break new ground. That's their job. That's what drives them. That's why scientific advancement happens. If they weren't generally open and very accepting of new ideas, we'd still think the sun revolved around the earth.

Nah. I'm 100% in opposition to that view of "scientists" (even if it were possible to group them all in such a way). Just look around at what you can see near you right now and say that scientists are opposed to new stuff. Think about the many massive discoveries over the years which radically change the way we view the universe. Do you really think a group of people who were by nature opposed to new things would figure out gravity, quantum mechanics, relativity, the accelerating expansion of the universe, the Big Bang theory, heliocentrism, or a million other things? Stuff about which everyone else cried "it can't be true!"?

There are people blinkered against new theories. Scientists are not those people.

 

[KarinsDad]

I think that's fairly insulting thing to say. Scientists are nothing like that; they're the very definition of the opposite. Scientists, in my experience, are pretty much the group most open to new things I've ever met. That's why scientific advancement happens. If they weren't generally open and very accepting of new ideas, we'd still think the sun revolved around the earth. The number of "new" ideas in the last century numbers in the hundreds of thousands in a thousand different scientific fields. Just because they haven't en-masse adopted your pet theory doesn't make them "close minded".

No. Scientists are very much NOT " blind to theories which don't match what they've believed most of their lives". In fact their very job is to research new theories.

Actually, I should qualify that statement. I do think that SOME scientists tend to be blind to theories which don't match what they've believed most of their lives. In fact, the reason that science took so long to get off the ground (so to speak) is because of firmly held belief of many scientists throughout time. The ancient Greeks could have gotten us maybe a half millenium more advanced today (course, none of us would actually be here) if they would have been as concerned about practical applications of science as they were about "abstract truth" of science (and philosophy and math). The steam engine could have easily been invented over two thousand years ago because steam powered toys existed.

There are many examples of scientists totally disagreeing on the exact same data. Look at Steady State vs. Big Bang. Both theories have had a ton of modifications since they were first proposed to match additional data (which is a reasonable thing to do), but obviously, they both cannot be correct. One of these ideas was only really dropped completely by almost all scientists in the last two decades. And in fact, it's possible that they are both incorrect and that the scientific community is misinterpreting the results being found.

There are also examples of peer review that dismissed research that was perfectly valid, but controversial.

Scientists are people too and can be just as dogmatic as any other person. They also get research funds for specific projects and if those projects start to falter, just like many other people, they can distort their conclusions of the data to more closely match the expectations. Not necessarily the falsification of data and maybe not even intentionally, but skewing conclusions or omitting inconsistencies to match current theory or to match a specific theory.

As Morris Kline wrote (talking about mathematicians): "Many were modest; others extremely egotistical and vain beyond toleration. One finds scoundrels such as Cardan, and models of rectitude. Some were generous in their recognition of other great minds; others were resentful and jealous and even stole ideas to boost their own reputations. Disputes about priority of discovery abound."

Do you really think that scientists are really that morally superior than anyone else? Do you think that anyone whose job is dependent on them acquiring results will not get results?

And even open mindedness in the scientific community means viewing new claims through the filter of established knowledge. Not true open mindedness, but open mindedness with hard wired caveats. And, this is how it should be. But, it does lead to a certain level of closed mindedness when doing so.

Obviously, not all scientists are close minded. Many are very open minded and try new things. But some do new experiments to support their theories, not to disprove them. And, there are examples of not just closed mindedness, but actual intellectual dishonesty.

Diederik Stapel
Jan Hendrik Schön
Hwang Woo-suk
Emil Rupp
Michael Bellesiles
Luk Van Parijs
Scott Reuben
Jon Sudbø


Just like all people, there are good scientists and bad ones. Open minded ones and ones who consider anyone who disagrees with them to be a fool. Ones who will argue with you and ones who will go "Hmmm, I hadn't considered that. Let's do an experiment.".

I don't think you can paint the entire scientific community with the broad brush of most scientists being the most open minded individuals around.

 

[Morrus]

Actually, I should qualify that statement. I do think that SOME scientists tend to be blind to theories which don't match what they've believed most of their lives. In fact, the reason that science took so long to get off the ground (so to speak) is because of firmly held belief of many scientists throughout time. The ancient Greeks could have gotten us maybe a half millenium more advanced today (course, none of us would actually be here) if they would have been as concerned about practical applications of science as they were about "abstract truth" of science (and philosophy and math). The steam engine could have easily been invented over two thousand years ago because steam powered toys existed.

There are many examples of scientists totally disagreeing on the exact same data. Look at Steady State vs. Big Bang. Both theories have had a ton of modifications since they were first proposed to match additional data (which is a reasonable thing to do), but obviously, they both cannot be correct. One of these ideas was only really dropped completely by almost all scientists in the last two decades. And in fact, it's possible that they are both incorrect and that the scientific community is misinterpreting the results being found.

There are also examples of peer review that dismissed research that was perfectly valid, but controversial.

Scientists are people too and can be just as dogmatic as any other person. They also get research funds for specific projects and if those projects start to falter, just like many other people, they can distort their conclusions of the data to more closely match the expectations. Not necessarily the falsification of data and maybe not even intentionally, but skewing conclusions or omitting inconsistencies to match current theory or to match a specific theory.

As Morris Kline wrote (talking about mathematicians): "Many were modest; others extremely egotistical and vain beyond toleration. One finds scoundrels such as Cardan, and models of rectitude. Some were generous in their recognition of other great minds; others were resentful and jealous and even stole ideas to boost their own reputations. Disputes about priority of discovery abound."

Do you really think that scientists are really that morally superior than anyone else? Do you think that anyone whose job is dependent on them acquiring results will not get results?

And even open mindedness in the scientific community means viewing new claims through the filter of established knowledge. Not true open mindedness, but open mindedness with hard wired caveats. And, this is how it should be. But, it does lead to a certain level of closed mindedness when doing so.

Obviously, not all scientists are close minded. Many are very open minded and try new things. But some do new experiments to support their theories, not to disprove them. And, there are examples of not just closed mindedness, but actual intellectual dishonesty.

Diederik Stapel
Jan Hendrik Schön
Hwang Woo-suk
Emil Rupp
Michael Bellesiles
Luk Van Parijs
Scott Reuben
Jon Sudbø


Just like all people, there are good scientists and bad ones. Open minded ones and ones who consider anyone who disagrees with them to be a fool. Ones who will argue with you and ones who will go "Hmmm, I hadn't considered that. Let's do an experiment.".

I don't think you can paint the entire scientific community with the broad brush of most scientists being the most open minded individuals around.

By that logic, I may as well say "messageboard posters are dishonest". What you're saying has nothing to with science or scientists at all; it's just people. Why did you choose to attach it to statement about scientists in particular, as opposed to football players or chess players?

I mean, it sounds like you have a beef with "scientists". That's three posts in a row where you've levelled different accusations at them. First it was their fault that educators and media portrayed hypothesis as fact; when I pointed out that it was unfair to blame them for that, you moved on to claiming they were all narrow-minded and opposed to new theories; and when I pointed out that they're not generally opposed to new theories, you say you didn't mean all of them, and switched to accusations of dishonesty. And before all that, you were attacking perfectly reasonable behaviour regarding hypothesis and interpretation of data because "it's possible" something could be wrong (which is obvious, but not a useful statement in any way). It really, really sounds like you hold some kind of grudge against the broader scientific community; I can't imagine what, though.

It's kinda odd. You've leapt into the thread blasting accusations at scientists around in this wild shotgun scatter pattern, with the accusations changing with each post. You've even implied that scientists are the ones responsible for slow progression of science, rather than the ones solely responsible for any progression at all.

If you think there's resistance to scientific progress out there - you're damn right there is! It's not the scientists though. There are plenty of other high profile obvious candidates for that particular problem.

Yeah, sure, there are bad apples in every vocation. So what? That's not a useful commentary on science, scientists, or scientific practice in any meaningful sense. I mean if that's all that those posts were building too - yeah, sure.

 

[the Jester]

Going back a few days, here's one example of the "not before the time machine was built" stuff:


[ame]http://www.youtube.com/watch?v=oRWwI61so5Q[/ame]