la flama blanca
Banned
And doesn't time not exist if we aren't around to experience it?
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how can astronomers know what's going on light years away if...
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The Technomancer
card-carrying scientician
Again, all dependent on your definition of time. My personal favorite is entropy just for that very reason.
Remember reading all that shit as a kid and wondering, why don't they just do that here? No more energy crisis. Hitch your wagon to a star
Gravity makes everything go...what a concept.
Personal time, I like to think, is just your brain recording impressions and telling you that you were a baby before you grew up etc.
Universal time is only defined by entropy like The_Technomancer said; an unchanging universe could not have a concept of time.
What's really amazing is there is nothing in the mathematical laws governing space and time to dictate this 'arrow of time'; they could work equally as well if the arrow of time were reversed. It's entropy that plays spoilsport; Brian Greene gives an example of the chance of the pieces of a cup magically reassembling to form a whole cup is vanishingly small, but not improbable. Whereas the probability of the reverse is as close as you can get to 1 without being 1.
Liquidsnake
Banned
This. They see the past and calculate what will happen in the future based on that. Of course, they can be wrong. Something unforeseen could happen in that time. But that's the only way to do it at the moment.
Great post.
The Technomancer
card-carrying scientician
Thanks. I read that in Fabric of the Cosmos when I was 15 and it was the first example that made time dilation make any kind of intuitive sense to me, as well as having the happy side effect of being my introduction into mentally comprehending higher dimensions. Of course now that I'm an engineer with computer science as a hobby I have to mentally work in 3+ dimensions all the time.
That's actually really crazy. Does that mean that the astronauts in that example were biologically .007 seconds younger? I'm not very eloquent when it comes to things like this, I apologize. In my mind it seems like them being .007 second "younger" would be an arbitrary value of age that we apply to them, not that .007 seconds were actually added to their lifespan (if that makes any sense)Dreams-Visions
Member
Yes, it does.
Dreams-Visions
Member
Also, for fun maths, if those same astronauts were traveling at half the speed of light for 6 months,
they would be ~1,972,307.88 seconds, or 22.83 days younger than they would have been had they stayed put. Give or take. If you were going at ~99% the speed of light (663,910,523 miles/hour) for 6 months, you would come back 3 months younger than if they had you stayed put. Everyone would have aged twice as much to their eyes. Imagine traveling at such a speed for 15 years aboard a space ship. Your clocks would say it's 2027 and you would have felt 15 real years go by. But landing back on Earth, the clocks would read 2042 and your old friends would look very old indeed...
(if I did that math correctly; not 100% confident)
they would be ~1,972,307.88 seconds, or 22.83 days younger than they would have been had they stayed put. Give or take. If you were going at ~99% the speed of light (663,910,523 miles/hour) for 6 months, you would come back 3 months younger than if they had you stayed put. Everyone would have aged twice as much to their eyes. Imagine traveling at such a speed for 15 years aboard a space ship. Your clocks would say it's 2027 and you would have felt 15 real years go by. But landing back on Earth, the clocks would read 2042 and your old friends would look very old indeed...
(if I did that math correctly; not 100% confident)
Foxy Fox 39
Banned
I find physics (quantum and astro) extremely interesting.
Its fun to think about light years. Taking the concept of looking at someone a few years away, think about if we were looking out into space at a dense cloud of gasses and dust appearing as they were billions of years ago and at that very moment if someone (and a planet) were to exist there, those non earthlings would look in our general direction and would see a cluster of gasses as well.
So if you believe in the possibility of alien life (somewhat comparable to humans) then there could be many of them living just as we do, looking out into the stars, feeling quite alone due to the "disingenuous" nature of light.
Its fun to think about light years. Taking the concept of looking at someone a few years away, think about if we were looking out into space at a dense cloud of gasses and dust appearing as they were billions of years ago and at that very moment if someone (and a planet) were to exist there, those non earthlings would look in our general direction and would see a cluster of gasses as well.
So if you believe in the possibility of alien life (somewhat comparable to humans) then there could be many of them living just as we do, looking out into the stars, feeling quite alone due to the "disingenuous" nature of light.
Yes, the astronauts really were that much "younger" due to the altered passage of time at high speeds. It also works for clocks and other time-sensitive processes like the decay of radio-isotopes.
Synless
Member
Every time I hear that it blows my mind. It's one of the most crazy things to think of.
I know it's incredibly simplistic and I will probably receive some corrections for that, but a friend of mine who is a physicist always used to say that when traveling at high speeds you're basically "escaping time". I love that mental image and to some degree I think it is a valid (albeit simplistic) description of what happens during velocity based time dilation.
The best part is that it's true and we can verify it. Also, the math involved is something that a high school freshman could do, given a little patience and an open mind.
[bill_nye]SCIENCE RULES![/bill_nye]
Foxy Fox 39
Banned
Cue the latest episode of The Nerdist (the one with Neil) and Startalk Radio.
Deadly Cyclone
Pride of Iowa State
Just wanted to drop in and say I love Astronomy. Would have attempted to major in it in college if there were more jobs in the field.
Any good astronomy books you all can recommend? Preferably books that don't read like textbooks?
Any good astronomy books you all can recommend? Preferably books that don't read like textbooks?
I don't know how much you're already into astronomy but you can never go wrong with any (new edition) Stephen Hawking book.
"A Brief History of Time" by Stephen Hawking for general mind-blowing stuff about the universe.
xclaw
Member
Anything by Carl Sagan. I am halfway through A Pale Blue Dot as of today..... Just amazing stuff.
This...bitch?
Dreams-Visions
Member
you found that comment necessary...why?
krameriffic
Member
No. This is a common misconception. Of all the things in all the world to be important in physics, point of view (in the parlance of the discipline, frame of reference) is the key concept in relativity. The most important thing for you to never ever forget is that you are never moving with respect to yourself. You are always in your own rest frame. If you're cruising along in a spaceship at a speed close to that of light, you don't feel any different than if you were driving in a car at 30 MPH. People who might be observing you from outside your spaceship will see time slow down for you. I don't actually know what it would look like, maybe like you are moving in slow motion.
It would take thousands of years to reach Sol?
I just find it incredibly funny how there's this shared discussion of higher education only for the poster to mar it by referring to the doctor in the video as a bitch, only because she's woman.
I think the more appropriate question is why the original poster felt that addition was necessary.
This talk reminded me of a really interesting episode of Stargate. A team is sent through the gate and arrives on a planet whose solar system is on the verge of being swallowed by a black hole. Time from the teams perspective remains the same, but to everyone back on Earth they're like statues because the time dilation is so great.
I think they get left there because there was no way to communicate with them or bring them back before Earth eventually got sucked through the gate. I've always thought that was a fascinating concept, even though I'm sure the physics and math don't work out at all.
I think they get left there because there was no way to communicate with them or bring them back before Earth eventually got sucked through the gate. I've always thought that was a fascinating concept, even though I'm sure the physics and math don't work out at all.
ANOTHER QUESTION, ANOTHER QUESTION LOL!!!! Okay, if lets say we are seeing light from a distant star 100 light years away, or maybe galaxy...doesn't matter. Anyway, the light from the star arrives today at some random time. Then lets imagine by some freak accident the star went supernova or galaxy was sucked in by a black hole immediately after the light had left. When would we know it no longer exists? How would we know? Would we just look up to the sky and poof its gone? How does it work? My way of thinking or asking this question may be wrong but someone feel free to clarify me. Thanks gaf.
So if you call time entropy, which i was calling change (vague i know), then how do you travel though entropy or change? ie time travel.
We wouldn't know that the star had exploded or gotten sucked into a black hole until we saw it flash or disappear respectively. These are also limited by the speed of light.
We would see the resulting explosion in the sky, just not for thousands of years after it occurred. Like everything is on a huge tape delay. We would see exactly what happened to it, just not for a long, long time.
Here's the part that I don't get. If it takes 6 months at half the speed of light to get to a location, does it take 6 months to get there relative to the pilot or relative to the location?
To clarify, will the person get there in 6 months but to them it felt like 5 months? Or will he actually get there in 5 months due to differences in space/time?
So what if the light escaping got sucked in by the black hole? Would it just vanish in the sky?
I don't think that's right, it's just that entropy and time correlate.
The Technomancer
card-carrying scientician
Yup, but we would still see it until thousands of years after it got sucked in, since all the light previous to that would still be traveling towards us.
lol nice.
Well, black holes usually have a hot, crazy region around them called an accretion disc that consists of all the stuff that's being drawn in, but hasn't passed the event horizon yet, so we may be able to detect that. Otherwise, yeah, the star would disappear.
Because entropy is a one-way process that's happening unevenly and affected by stuff like relativistic speeds, you can't travel along the "time axis" in the same way you can spatial axes like x, y, and z. That's where the "arrow of time" comes from.AiTM said:
Dreams-Visions
Member
we would know it's gone because its light would stop coming. just like how you know your candle goes out in your home.
in the case of a supernova, we'd see a spectacularly bright light, which we would easily recognize as a supernova. and because we would have known how far said galaxy was away from us already, we'd know how long ago the explosion took place. trust me, we'd know if a star went supernova. it'd be the brightest light in the sky. we would also begin to see the creation of the nebula surrounding the newly formed neutron star.
as for the black hole, I assume we'd see a bright explosion, a briefly bright neutron star...then we'd see nothing as gravity wins and crushes the super-massive, super-dense star. That chain of events should be pretty much proof positive of what happened, and detection of powerful x-ray particle jets should be the final confirmation (if we can detect them from our distance). I don't believe we've ever actually witnessed this happen, so it's all just a really confident theory at this point.
iirc.
Your post reminded me something interesting about black holes. Even though the gravity pull of a black hole is so great that light cannot escape from it, the force of gravity actually does not increase.
So for example, if our sun instantly becomes a black hole. Theoretically, our solar system will still orbit around the now black hole. Ignoring the obvious issues of the lack of a sun, the force of gravity would be the same as if our sun was there and the earth would not get pulled in.
Well, not exactly. If a star spontaneously turned into a black hole without absorbing any extra mass, stuff that's relatively far away from it wouldn't be affected that much. Black holes do, however, have what's called an event horizon, which is the radius at which gravity is too intense for anything to ever get out. Since creating a black holes generally involves adding a bunch of mass, it would accumulate and get stronger gravity as it "ate" more stuff.
It takes 6 months relative to our (Earth's) reference frame.
If another star is 99 light years away and we send a spaceship at 0.99c, we can observe it moving towards that point over the course of 100 years. If you were to put clocks onboard that spaceship, they would read much less than 100 years, however.
The only thing that would look weird to us, viewing from the outside, is that the spaceship would appear to be contracted in length, as objects get compressed over their axis of travel according to relativity.
And this is exactly why these packets contain the same information after travelling light years.Acullis said:
If time were perceptible to the photon what we see in the distant night sky 1000 light years away wouldn't be stars as they were years ago but stars as they were 1000 years ago + random corruption from the cosmos (both time and space)
The whole universe would be all staticky
Dreams-Visions
Member
I'm not sure about this, sir. A light photon will contain the same information because it's massless and because it doesn't interact with Higgs or any other subatomic particles.
or am I wrong?
Well, the photon is subject to stuff like redshift and blueshift, the optical equivalents of the doppler effect when the distance between the photon and its destination grows or shrinks, respectively. That's more timespace monkey-business than "degradation," though.
That could make a good movie: aliens see us during Dark Ages, assume we suck, then fly out to conquer us. Oh wait it's now 2020 and we give them a heck of a fight and end up pulling it out due to the courage and valor of one squad of US Marines.
There's a sci-fi story about FTL travel being ridiculously easy to develop, but the civilizations of Earth never figured it out for whatever reason. In the mid 21st century, we get invaded by aliens who did figure out spaceflight and FTL travel, but whose weapon and armor technology are equivalent to those of what we were using during the Renaissance. Earth fights back and soundly crushes the invaders.
bigboss370
Member
So essentially when we see a comet in space flying through the sky, in that exact moment we are seeing it, the comet has already passed the area we're looking at long ago?
cool
Doesn't gravity go against entropy then? Since right after the big bang gravity pulled all the gas/dust from disorder into galaxies and planets(order) ?
I don't think this would happen, because the closer they come to us, the faster light would reach them, therefore time would essentially 'catch up'.
maybe thats what religion is referring to when it says God created man from dust
cool
Doesn't gravity go against entropy then? Since right after the big bang gravity pulled all the gas/dust from disorder into galaxies and planets(order) ?
I don't think this would happen, because the closer they come to us, the faster light would reach them, therefore time would essentially 'catch up'.
maybe thats what religion is referring to when it says God created man from dust
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