QUOTE (Stellar @ May 20 2008, 06:16 PM)

The jury is still out on that one!
Not really. Sending information into the past violates causality, period.
Such a thing is nonsensical.
If you propose that this nonsensical thing is "possible" in some weird sense, then
you must propose an alternative model of causality to that which is used in science.Until then, "time travelers from the future" is just another incoherent or irrational proposition. It is exactly like an explanation requiring that the same thing was in two places at once, or that two different things were in the same place at once. Strictly speaking, not sensible.
There is no such problem with the proposition that nonhuman intelligences exist and have come here aboard craft.
This makes me wonder why you would favor time travelers over ET as a possible explanation or even place them in the same category.
QUOTE
You're telling this to a 3rd year university physics student

Yes, I am. Why is it necessary to inform you of a famous paradox? Why is a Junior in physics placing "travelers from the future" in the same category of plausibility as extraterrestrial intelligence?
QUOTE
1. According to our known physics, faster than light travel is also impossible. How likely is it that aliens would travel dozens of years if not more to travel to Earth and not make contact?
That is difficult to calculate, isn't it? But as long as it isn't strictly nonsensical, it has a big leg-up on time travelers from the future.
Second, who insists that if ETs are here, they have not "made contact?" Haven't they, indeed, according to proponents of the ETH?
Do you mean to ask why certain elements of the security establishment would refuse to acknowledge such contact, if it has taken place?
I hope you can imagine an answer to that one.
Third, many things that
seem supremely unlikely according to our best calculations are matters of bland fact. As a third-year physics major, you should be able to think of a number of examples offhand. Assigning a low probability to an event-- especially in such an arbitrary manner as you've done here--
never, ever rules out its occurrence. Indeed, "unlikely" events occur
all the time.QUOTE
2. Everything is a possibility, including time-travelers.
Weak. To make "time travelers from the future" a plausible hypothesis, you'll have to explain a way around paradox of causation. Until you (or anyone) manages that, it is just another instance of gibberish, like being in two places at once.
Again, the ETH, whatever its other problems might be, does not suffer from any such glaring logical flaw. So I have to wonder why it's dismissed with such prejudice by people who call themselves skeptics, while half-baked sci-fi and conspiracy theories are aired so carelessly.
Sometimes they aren't even half-baked.