Is Time Travel (going backwards) Possible?

[Umbran]

I was given to understand that's the name which was catchy enough to catch no with the newspapers and the like and that there were dozens of names floating round until the media effectively made the call.

There are dozens of fanciful names for the possible specific forms of dark matter. I, personally, am a fan of WIMPs* and MACHOs**. Physicists tend to be fanciful - we call things "quarks" and bet each other if we can get away with using odd words in papers, leading to the "penguin diagram".

But for the overall terms "dark matter" and "dark energy", I don't recall there were really any major contenders. They were coined by Fritz Zwicky (in 1933) and Michael Turner (in 1998, recalling Zwicky intentionally) respectively.



*Weakly Interacting Massive Particles
**Massive Compact Halo Objects

 

[Dannyalcatraz]

Physics needs more DAMNs.*






* Dorky Acronyms Meaning Nothing

 

[Umbran]

And, it being All Hallow's Eve, this seems particularly relevant:

"Benjamin K. Tippett has a theory. The University of New Brunswick mathematician believes that he’s figured out what, exactly, those insane sailors saw that night in 1928 when they encountered Cthulhu on a lost island in the Pacific. And so Tippett has written a hilariously deadpan paper explaining “non-Euclidean geometry” once and for all."

Possible Bubbles of Spacetime Curvature in the South Pacific

The final conclusion - that only entities capable of FTL travel (and thus spacetime cloaking and time travel) could generate the observed phenomenon - is quite interesting...

 

[Corathon]

I can't think of how to present the logical flaw here more clearly: I recognise it, but my literary style is not up to the task. But there's a fundamental logical flaw in those two sentences, located in the logical fallacy of demanding proof of the negative (impossible). All I can say is - demanding that I disprove you is not proof of your assertion. Don't say "prove me wrong"; prove you're right.

I think that proving I'm right might be a logical impossibility; the old "you can't prove a universal negative" thing.

There's an alien from Neptune behind my couch. Prove me wrong.

Were I at your house I could look behind the couch.

Alpha Centauri is made of chocolate. Prove me wrong.

I think that spectroscopic evidence pretty well rules that one out.

The ghost of Henry VII visited me last night. Prove me wrong.

I can't, as I wasn't with you last night.

I am Superman. Prove me wrong.

If we were in the same room, that would be fairly easy; I could take a pin and poke you. Not that I'd do such a thing, because I'm pretty sure that you're not actually Superman.

Dark Energy is created by the psychic fields of aliens working at Walmart. Prove me wrong.

I can't prove you wrong on that one - but "dark energy" is pretty much a label for ignorance anyway.

I can't prove you wrong. But I don't have to. A claim has to be proved right.

As I said above, one counterexample proves me wrong. I guess that we just have to agree to disagree on this.

 

[Thotas]

As for what it is - it is energy that is in a form that causes no impact currently measurable on short distances, but that in aggregate has a repulsive effect over very large distances.

Right, but isn't that more a description of the situation than an explanation for the effect? "Oh, look, there's a repulsive effect adding up over large distances that is unnoticeable at (cosmic scale) small distances." And since that's work, there has to be an energy responsible because the potential to do work is more or less the definition of energy in physics. Last I heard, it was pretty well agreed that there's more to find out there ... of course, with science, we always find out there's more to find out there.

 

[Morrus]

As I said above, one counterexample proves me wrong. I guess that we just have to agree to disagree on this.

On the burden of proof? Yes, I guess so. You made the claim. You may have heard the phrase "If this responsibility or burden of proof is shifted to a critic, the [logical] fallacy of appealing to ignorance is committed".

 

[Umbran]

Right, but isn't that more a description of the situation than an explanation for the effect?

Yes, but that's most of science. The difference between describing the situation and explaining the effect is how much information you have - when you have enough information, the description *is* the explanation.

 

[Thotas]

Yes, but that's most of science. The difference between describing the situation and explaining the effect is how much information you have - when you have enough information, the description *is* the explanation.

And again, I get that ... I guess what I'm saying is that it's my understanding that physicists don't think they have enough info to unify description and explanation into one thing on this issue. I'm one of those guys who reads a lot of lay science books and wishes news media did a better job of reporting on science both in terms of quality and quantity, but a long way from being any kind of expert. But when the experts are saying something needs better explanation, I tend to think it must.

 

[Umbran]

As I said above, one counterexample proves me wrong. I guess that we just have to agree to disagree on this.

The point, though, is that you don't get to make an unsupported assertion, and say, "I am right unless you prove me wrong." In general, burden of proof sits with the person who makes the assertion - if you can't support it, you shouldn't make the assertion.

Let us see if we can put this one to bed: General relativity allows some forms of time travel, in the sense that it doesn't itself actively prohibit them. GR allows for a solution that has a wormhole from point A to point B, for example.

GR doesn't speak to how that wormhole is created, however. GR does not actively prohibit a box with a big red button on it that creates a wormhole to a specified point in the past. Thus, GR allows time travel to arbitrary times before the machine was created, in the same sense that it allows time travel at all.

 

[Umbran]

I guess what I'm saying is that it's my understanding that physicists don't think they have enough info to unify description and explanation into one thing on this issue.

And you'd be entirely correct in that. No argument there.