More space news!

[Old Man]

Geminids tonight if you can stay up that late.  (Or if you're tkdguy and you never sleep anyway.)

[L. Marcus]

I'm staying up, but at work. No time for stargazing. 

[tkdguy]

8 hours ago, Old Man said:

Geminids tonight if you can stay up that late.  (Or if you're tkdguy and you never sleep anyway.)

 

I'll most likely be up tonight, but the last few times I went out looking for meteors, all I got out of it was a sore neck.

[Old Man]

Managed to see two or three small ones before the clouds started rolling in.  Now to see if my wishes come true.

[tkdguy]

I saw one bright meteor and a couple of dimmer ones. I didn't stay outside very long, however.

[DShomshak]

The January, 2018 Scientific American has an article about an experiment due to start soon, that seeks to detect a hitherto-hypothetical particle called the axion. What's an axion? Well, read the article. The important thing is it's a dark matter candidate. Since several experiments have failed to find any evidence of Weakly Interacting Massive Particles, the axion is looking like a better candidate, and physicists finally think they've found a way to detect a particle so inert it makes the neutrino look highly reactive. Stay tuned.

 

Dean Shomshak

[dmjalund]

The experiment is to be done in an upper level to be called the axion-attic

 

J.K.

[Old Man]

Saw the supermoon rise last night, briefly, before the change overcame me and the hunt began.

[L. Marcus]

Awooo, and so forth.

[Christopher]

16 minutes ago, Old Man said:

Saw the supermoon rise last night, briefly, before the change overcame me and the hunt began.

Are Supermoons like Superfood?

 

[tkdguy]

6 hours ago, Old Man said:

Saw the supermoon rise last night, briefly, before the change overcame me and the hunt began.

 

I knew there had to be a reason I couldn't bring myself to shave that day!

[DShomshak]

23 hours ago, Old Man said:

Saw the supermoon rise last night, briefly, before the change overcame me and the hunt began.

Well, you know how the various full moons through the year have traditional names, of which the Harvest Moon is the most famous? Well, I heard on the radio that this was... the Wolf Moon.

 

The Chinese lunar calendar says this is the Year of the Dog. But with the Wolf Moon on the first days of the year -- and a supermoon besides! -- I say this is the Year of the Wolf.

 

Expect trouble.

 

Dean Shomshak

[Cancer]

Convective cells imaged on pi 1 Gruis

An S star

[L. Marcus]

S is for "silly".

[Cancer]

No, in this case, S doesn't stand for anything.  I think it was the first unused spectral class designation letter at the time the class was defined.

[Zeropoint]

I'm very impressed that we can get a picture of another star as more than just a point of light!

[Christopher]

Comedy shows are not normally a source for information, but this time they had Niel De Grasse Tyson on air. And he talked about something:

 

So the expansion of hte universe is accelerating, due to something called Dark Energy (because they really have no idea what it is).

And if it keeps accelerating like this, sooner or all the other galaxies around is will become invisible. The expansion becomes faster then light, so the light from those galaxies no longer reaches us.

All we know about our universe, we know from observing those distant galaxies. A whole chapter of Astrology will be ripped from future Astronomers. And that raise one question:

Maybe this was not the first time a chapter will be lost? Maybe we do not have the complete picture of the Universe, because Light (or somethign slower) does not move fast enough to outpace expansion?

 

Let us hope we figure out FTL. Then we might have a chance to look at it from a different perspective.

[Zeropoint]

It's common in discussions of FTL for people to trot out the saying "relativity, causality, FTL: pick any two." General Relativity tells us that FTL is equivalent to time travel, and time travel means that causes no longer precede effects and . . . well, the words "wibbly wobbly" seem appropriate here. Given that General Relativity has been experimentally verified to the point that only a kook could deny it, this leads many people to the conclusion that FTL can't possibly exist, because we certainly have causality, right?

 

Except . . .

 

First, as far as I can see it with my layman's lack of specialized knowledge, causality doesn't have to apply ALL the time for the world to make sense. Relativity tells us that Newtonian physics are wrong, for instance. However, people lived by Newtonian physics for a long time before Einstein, and the world didn't fall apart when the suddenly discovered that they'd been wrong about everything . . . and people still use Newtonian principles for a lot of practical applications. That's because, despite the fact that Newtonian physics is clearly not correct, under normal circumstances the errors are incredibly tiny, and the circumstances under which the errors would be significant are uncommon in day to day life. Why should causality be any different? Would we notice the difference between a world where causality applies all the time and one where it applies very nearly all the time?

 

Second, (and once again with the caveat of my limited knowledge) it's my understanding that theoretical physicists have determined that time travel, at least on a limited scale, is definitely physically possible. If we live in a world where transmission of information into the past is possible, even if extremely difficult and unlikely, then we ALREADY live in a world where causality doesn't hold, and there's nothing to give up by "picking" relativity and FTL.

 

Still, I don't expect to be able to visit Alpha Centauri in my lifetime. Sigh.

[Christopher]

17 hours ago, Zeropoint said:

Given that General Relativity has been experimentally verified to the point that only a kook could deny it, this leads many people to the conclusion that FTL can't possibly exist, because we certainly have causality, right?

One thing I never got actually: How does timetravel break causality?

For me there is no break in causality at any moment. So what if the cause comes from a "alternate future that can no longer come to pass this way"? That is still a clear cause - effect realtionship to me. Space Time coordiantes start getting a bit wierd, but aside from that everything seems normal for me.

 

I mean I do not observe the generator providing power for my Computer right now. The cause of the power is not any more visible then the cause of the timetravel related effect. Yet the effect is quite real to me anyway.

[DShomshak]

Well, philosophers have been trying to define what exactly we mean by "cause" and "effect" since, um, Aristotle? Causality is one of those ideas that looks super-easy and obvious at first glance, but when you try to pin them down get shifty.

 

For that matter, Wikipedia's page on "Unsolved Problems in Physics" lists "What is time?" as one of the first and biggest. The flip answer is, "Time is what keeps everything from happening at once." And of course it's one of the fundamental dimensions and quantities in physics. But what time *is,* and why it works the way it does, remains unknown. And can you really understand causality if you don't really understand time?

 

And when I try to understand how entities exist as world-lines threaded through four-dimensional space-time, my head starts spinning. Then I quit and go get a cookie.

 

Dean Shomshak

[L. Marcus]

... Low blood sugar?

[Zeropoint]

People assume that time is a strict progression of cause to effect, but *actually* from a non-linear, non-subjective viewpoint - it's more like a big ball of wibbly wobbly... time-y wimey... stuff

[Christopher]

14 hours ago, DShomshak said:

And when I try to understand how entities exist as world-lines threaded through four-dimensional space-time, my head starts spinning. Then I quit and go get a cookie.

Then you are like captain Janeway in that regard:

 

[Cancer]

On 1/7/2018 at 6:25 AM, Christopher said:

One thing I never got actually: How does timetravel break causality?

For me there is no break in causality at any moment. So what if the cause comes from a "alternate future that can no longer come to pass this way"? That is still a clear cause - effect realtionship to me. Space Time coordiantes start getting a bit wierd, but aside from that everything seems normal for me.

 

I mean I do not observe the generator providing power for my Computer right now. The cause of the power is not any more visible then the cause of the timetravel related effect. Yet the effect is quite real to me anyway.

 

There is nothing you can do *now* that can change the conditions in your past (you cannot now do something to the generator, power lines, etc., so that your computer instead of working 10 days ago was non-working instead).  Time travel would permit that contradiction of experience, such that your post was registered here with the timestamp we now observe, yet the computer which allowed you to post it was not functional at that instant.  Should your post have vanished when you interrupted, "after the fact", the causal train that initially created it?  And if so, did some subsequent alteration of the timestream occur to overrule that interruption, so that the post occurred anyway?  And is there anything that rules out infinite recursion in this cause/prevention chain?

 

One can construct an argument that FTL motion implies simultaneous existence in infinitely many places for the object that moves at FTL.  Now you're violating all kinds of conservation laws, things which we have tested throughout our history and have always been found valid.

[Cancer]

The tension between astronomical measurements of the Hubble Constant (the present rate of expansion of the Universe) and the value that comes out of analysis of the inhomogeneities in the cosmic microwave background (from the Planck satellite mission) is getting worse.  A direct calibration of the Cepheid distance scale by parallax measurements of seven long-period Cepheid variables, affirming the HST result obtained back in the 1990s and tightening its error bars, was submitted two weeks back.  The two values are 73.45+/-1.66 km/s/Mpc for the new Cepheid distance scale, compared to 67.74±0.46 in the same units from Planck; that's a 3.7-sigma discrepancy.  That's enough to start getting interesting and/or annoying.

 

Cosmology may not be as solved a problem as has been asserted.