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Wed Feb 13, 2013, 12:36 PM

Ok, here's one for the cosmologists

Been reading a lot about quantum mechanics lately. (Brian Greene) and this hypothetical question baffles me.

1. A cosmologist looks at a star through a high powered telescope.
2. The star is a long, long ways away.
3. It takes the light from that star 1 million years to travel
from that star to the telescope lens, thus the viewer is looking at that star as it was 1 million years ago.
4. Assuming that the laws of physics are correct, that would mean that any calculations concerning this star's nature is based
on 1 million year old information.
5. If all of this is true, then we can never really know the CURRENT nature of this star. It could have turned into a giant black and white hamster and we would never know it. lol

thoughts?

49 replies, 2758 views

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Arrow 49 replies Author Time Post
Reply Ok, here's one for the cosmologists (Original post)
clarice Feb 2013 OP
marybourg Feb 2013 #1
clarice Feb 2013 #4
Cary Feb 2013 #8
marybourg Feb 2013 #12
clarice Feb 2013 #21
cleanhippie Feb 2013 #2
Cary Feb 2013 #6
cleanhippie Feb 2013 #31
Cary Feb 2013 #37
cleanhippie Feb 2013 #40
Cary Feb 2013 #45
Cary Feb 2013 #39
clarice Feb 2013 #7
cleanhippie Feb 2013 #32
Cary Feb 2013 #3
Moonwalk Feb 2013 #5
NRaleighLiberal Feb 2013 #9
Viva_La_Revolution Feb 2013 #10
Sekhmets Daughter Feb 2013 #11
DreamGypsy Feb 2013 #15
clarice Feb 2013 #17
Sekhmets Daughter Feb 2013 #19
DreamGypsy Feb 2013 #34
Sekhmets Daughter Feb 2013 #35
DreamGypsy Feb 2013 #43
Sekhmets Daughter Feb 2013 #46
cleanhippie Feb 2013 #41
Sekhmets Daughter Feb 2013 #42
cleanhippie Feb 2013 #44
Sekhmets Daughter Feb 2013 #47
cleanhippie Feb 2013 #48
Sekhmets Daughter Feb 2013 #49
clarice Feb 2013 #20
Sekhmets Daughter Feb 2013 #22
clarice Feb 2013 #24
Sekhmets Daughter Feb 2013 #27
DreamGypsy Feb 2013 #36
Sekhmets Daughter Feb 2013 #38
clarice Feb 2013 #26
Sekhmets Daughter Feb 2013 #28
clarice Feb 2013 #29
Sekhmets Daughter Feb 2013 #30
clarice Feb 2013 #33
DreamGypsy Feb 2013 #13
Sancho Feb 2013 #14
clarice Feb 2013 #18
clarice Feb 2013 #16
Confusious Feb 2013 #23
clarice Feb 2013 #25

Response to clarice (Original post)

Wed Feb 13, 2013, 12:38 PM

1. So what's the question?

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Response to marybourg (Reply #1)

Wed Feb 13, 2013, 12:44 PM

4. question

How can we make accurate predictions on the CURRENT state
of the star based on visual information that is 1 million years
old ? Everything that the observer is recording is based in the very distant past.

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Response to clarice (Reply #4)

Wed Feb 13, 2013, 12:50 PM

8. Actually we can go back a lot further than 1 million years.

What makes you think knowledge is about making accurate predictions?

How can we know what we perceive as being the present without understanding what we perceive to be the past?

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Response to clarice (Reply #4)

Wed Feb 13, 2013, 12:53 PM

12. google "Hertzsprung-Russell (H-R) diagram"

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Response to marybourg (Reply #12)

Wed Feb 13, 2013, 01:23 PM

21. Just googled it. WOW !!!! Thanks

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Response to clarice (Original post)

Wed Feb 13, 2013, 12:43 PM

2. Sounds about right.

Even light from our sun takes 8 minutes to get here, so we never really know the "current" nature of it, only why is was 8 minutes ago.

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Response to cleanhippie (Reply #2)

Wed Feb 13, 2013, 12:48 PM

6. What makes you think we would know the "current" nature even if we saw the light instaneously?

What exactly is light? What is matter? What is energy? What is space? What is time?

We are not objective beings. We are only subjective beings trying our best to be objective.

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Response to Cary (Reply #6)

Wed Feb 13, 2013, 02:34 PM

31. We could take that conversation to the philosophy group.

I hardly see it as relevant when discussing in this one though.

But excellent points.

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Response to cleanhippie (Reply #31)

Wed Feb 13, 2013, 03:19 PM

37. There's not that much difference between philosophy and physics these days. n/t

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Response to Cary (Reply #37)

Wed Feb 13, 2013, 03:41 PM

40. How so?

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Response to cleanhippie (Reply #40)

Wed Feb 13, 2013, 03:54 PM

45. Ever heard of Schrodinger's Cat? n/t

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Response to cleanhippie (Reply #31)

Wed Feb 13, 2013, 03:37 PM

39. The OP was a question about not knowing the true nature because we "see" light through time & space.

Obviously I think the author of the OP is correct to wonder about the universe, but that author of the OP is a little off in terms of the scope of the problem. It's not that we're seeing things after the fact. It's that what we think is "the fact" is actually an illusion.

On the other side of that is the human brain, which is capable of things way beyond "the facts". In nature we cannot travel the speed of light. We have no such barriers in the realms which are our minds.

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Response to cleanhippie (Reply #2)

Wed Feb 13, 2013, 12:48 PM

7. So, following this logic...

That distant star may not even be there anymore
*shakes head*

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Response to clarice (Reply #7)

Wed Feb 13, 2013, 02:37 PM

32. Certainly possible, and depending on its age as we see it...

It could be plausible. Astronomers have identified thousands of distant stars that are likely candidates to be supernovas right now, even though we see them as stars.

Mind boggling, huh?

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Response to clarice (Original post)

Wed Feb 13, 2013, 12:44 PM

3. There are a lot of things we will probably never know. n/t

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Response to clarice (Original post)

Wed Feb 13, 2013, 12:46 PM

5. All true! We can't know the current nature of the star--only it's past nature. That said...

...we do know enough about the life cycles of stars--and might know enough about the past nature of that particular star (i.e. our telescopes and such could tell us enough about its make-up, size, type, age, etc.) to have a good estimate as to it's current nature (i.e. a million years later, in our "now"). After all, stars go on for billions of years, and a star isn't likely to change that much in a million years. If it is likely to change that much--i.e. it's on the verge of collapse, there will likely be indications there in its current state to tell us that it might have collapsed, etc.

Obviously, the trickiest stars are the ones that we're gazing at from the distance of a billion light years or more. Those are the stars most likely to be shadows/ghosts, no longer there in the now. We're looking into the distant past of what was. Cool, huh?

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Response to clarice (Original post)

Wed Feb 13, 2013, 12:50 PM

9. boggles the mind, doesn't it! take it a step further....

you look at the sky on a dark, moonless night and see countless stars. And each one is its own particular distance from us - so the patterns you see don't truly exist (in terms of a particular time) - just on earth, to us, on a particular date - a skyful of historical images - and none of it reflective on what's going on in any particular star's neighborhood!

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Response to clarice (Original post)

Wed Feb 13, 2013, 12:51 PM

10. correct.

By observing different types of stars, all in their various stages, we can hypothesize about what it actually looks like now. But we'll never see it in real time.

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Response to clarice (Original post)

Wed Feb 13, 2013, 12:53 PM

11. And you are following Quantum Mechanics?

I have no problem wrapping my head around the fact that our sun could be gone 8 minutes before we would see the absence, for example. I have difficulty getting my head around the fact that we can never know where something is because it is in several places at the same time. I wish the damned car keys would just appear wherever I am looking for them.

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Response to Sekhmets Daughter (Reply #11)

Wed Feb 13, 2013, 01:09 PM

15. I find the energy transfer time in the sun (and all stars) to be even more interesting...

...than the travel time once a photon has escaped.

From Wikidedia, Solar Core:

Energy transfer

The high-energy photons (gamma rays and x-rays) released in fusion reactions take a long time to reach the Sun's surface, slowed down by the indirect path taken, as well as by constant absorption and reemission at lower energies in the solar mantle. Estimates of the "photon travel time" range from as much as 50 million years to as little as 17,000 years. However, the concept of photon travel is not a well-defined one, since photons are not conserved, and one photon at a high temperature normally turns into many photons at a lower temperature, during passage of heat out of the solar core to the Sun's photosphere. The long periods of time (tens of millions of years) refer to the characteristic time for the entire solar temperature distribution to change, as a result of changing heat generation rate in the core. This is far longer than the average time for transport of heat through the Sun because most of the Sun's heat capacity is in the kinetic energy of the particles in its plasma, not in the electromagnetic radiation present within it. The shorter estimates of photon travel time (tens of thousands of years) refer to the relatively rapid mean time needed for radiation to travel from the center of the Sun to the photosphere, even though the Sun's heat cannot pass from core to surface at this rate, due to the large heat capacity needed to be heated or cooled in the process, as mentioned above.

After a final trip through the convective outer layer to the transparent surface of the photosphere, the photons escape as visible light. Each gamma ray in the Sun's core is converted into several million visible light photons before escaping into space. Neutrinos are also released by the fusion reactions in the core, but unlike photons they very rarely interact with matter, so almost all are able to escape the Sun immediately. For many years measurements of the number of neutrinos produced in the Sun were much lower than theories predicted, a problem which was recently resolved through a better understanding of the effects of neutrino oscillation.


Cool, huh??

Ouch, I just got hit by a 45,000 year old photon. They get real grumpy when they're that old.

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Response to DreamGypsy (Reply #15)

Wed Feb 13, 2013, 01:11 PM

17. Very cool....*head explodes*

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Response to DreamGypsy (Reply #15)

Wed Feb 13, 2013, 01:17 PM

19. Yes it is wicked cool.

I love the "How the Universe Works" series.

Neutrinos are fascinating as well:

Neutrinos have no electrical charge. They're produced in vast numbers in some nuclear reactions, such as those that occur in the fusion processes that light the stars. But neutrinos rarely interact with other matter. Neutrinos produced by the sun can, and routinely do, pass through the entire earth without interacting with a single atom.

There are three kinds of neutrinos: electron, muon and tau. The heaviest neutrino could weigh as little as one ten-millionth the mass of an electron.

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Response to Sekhmets Daughter (Reply #19)

Wed Feb 13, 2013, 02:51 PM

34. Right. And if the sun woke up and decided it was tired...

...of fusion, fusion, fusion. Everyday just the same old thermonuclear process, 4.57 billion years worth. And suppose the sun decided to just stop!! (Of course, our sun wouldn't really do that...that's not among the ways stars die.)

If that happened, then how long would it be before we earthlings knew we might be in a bit of trouble?

Well, if we relied on energy transfer, then it could take a 100,000 years, or maybe just 17,000, before any measurable difference in electromagnetic radiation was apparent. There might be some other observational change that would hint at the problem - magnetic flux changes, or sunspot activity...I don't know, but stellar structure/behavior experts might.

However, our friendly little neutrinos would be trying to tell us almost immediately - after that ~8 minute travel time during which we receive the sun's final dose, all solar neutrinos following that would be intermittent travelers. Since we detect about 1 solar neutrino per day on earth, out 5 billion per square centimeter per sec, we would probably figure out with in a matter of weeks that something had changed. That would allow us a reasonably long time to stock up on firewood for the long cold winter which would eventually arrive.

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Response to DreamGypsy (Reply #34)

Wed Feb 13, 2013, 03:02 PM

35. Fusion, fusion, fusion... DreamGypsy that is hilarious!

Wouldn't we know 8 minutes and 18 seconds later, when it became unexpectedly dark at noon, or the moon suddenly blinked out of the night sky?

I have Alex Filippenko's lectures "Understanding the Universe"...I really must get around to watching them soon.

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Response to Sekhmets Daughter (Reply #35)

Wed Feb 13, 2013, 03:47 PM

43. The Universe in 96 Beers...

Hi, Sehkmets Daughter,

The energy transfer out of the sun takes (according to the data/caveats from the wikipedia article I posted) between 17,000 and 50 million years to escape the body of the sun. That means, if the thermonuclear filament burned out, the bulb would still be illuminated until all the contained energy escaped. No immediate darkness at noon, no loss of moonlight, Mars light, or Neptune light for a long time.

I am major a Alex Filippenko groupie. I acquired the Understanding the Universe: An Introduction to Astronomy, 2nd Edition from the Teaching Company in Spring 2008. My wife was departing on long trip to Australia (business and family), so I anticipated a need for some evening entertainment, learning, and company. A couple days after she left I sat down, with a beer, and watched the first of the 96 lectures. Same the next night. Some of the early lectures didn't give me much new information, but Alex was very entertaining and enthusiastic and the material reminded me of a some important concepts that had blurred or slipped away. Pretty soon was doing 2 lectures per evening...and, uh, two beers. Around lecture 50 the lectures were including a lot of information about findings and conclusions after 1990 or so, which is when I stopped reading Sky and Telescope and Astronomy and buying books on cosmological topics. Yup, three lectures/three beers ensued. The last 10 lectures blew me away.

Allocate some time, invite your friends in, stockpile your beverages of choice, enjoy Alex. It's a wonderful trip.

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Response to DreamGypsy (Reply #43)

Wed Feb 13, 2013, 04:01 PM

46. I shall begin this weekend...

or perhaps sooner... I have all the time in the world as I am retired.... I just need to stop playing on DU.

Thanks for the input.

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Response to Sekhmets Daughter (Reply #19)

Wed Feb 13, 2013, 03:43 PM

41. That IS a great series!

Very educational and informative, in a language most can easily understand.

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Response to cleanhippie (Reply #41)

Wed Feb 13, 2013, 03:45 PM

42. Hey cleanhippie,

Are you enjoying the updates?

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Response to Sekhmets Daughter (Reply #42)

Wed Feb 13, 2013, 03:49 PM

44. Not sure what you mean.

I'm on my phone, so maybe I'm missing something. Not following you at all.

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Response to cleanhippie (Reply #44)

Wed Feb 13, 2013, 04:04 PM

47. They have updated

the series "How the uni works" I've been watching for years and this year many of the titles are the same or similar but there is new information, including little boxes of info in the bottom left corner.

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Response to Sekhmets Daughter (Reply #47)

Wed Feb 13, 2013, 04:16 PM

48. Ahh, I see. No, I haven't seen a new episode in a few months or more.

I will have to check it out. Thanks for the heads up!

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Response to cleanhippie (Reply #48)

Wed Feb 13, 2013, 04:21 PM

49. You're welcome! n/t

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Response to Sekhmets Daughter (Reply #11)

Wed Feb 13, 2013, 01:19 PM

20. You are reffering to the...

double slit electron experiment ? The electrons behave differently when you observe them? lol WTF ???

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Response to clarice (Reply #20)

Wed Feb 13, 2013, 01:28 PM

22. Yep.

I know it's crazy isn't it? I think it was Einstein who first postulated that the mere observance of something changed its behavior and properties. Photons can be particles or they can be rays. I think if I ever really studied Quantum Physics I'd become schizophrenic.

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Response to Sekhmets Daughter (Reply #22)

Wed Feb 13, 2013, 01:36 PM

24. I might be wrong, but

I thought Einstein was against the whole "quantum" thing.

"God doesn't play dice with the universe"

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Response to clarice (Reply #24)

Wed Feb 13, 2013, 01:57 PM

27. He had trouble believing his own theories....

which led to quantum mechanics! You're also correct that it wasn't Einstein, but I don't remember who it was ...

You might enjoy this brief article.

http://discovermagazine.com/2008/mar/10-einstein-didnt-grok-his-own-revolution#.URvf8-jXHJw

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Response to Sekhmets Daughter (Reply #27)

Wed Feb 13, 2013, 03:15 PM

36. Planck and Einstein

Max Planck proposed the initial idea which led to quantum mechanics:

From Wikipedia:

Black-body radiation

In 1894 Planck turned his attention to the problem of black-body radiation. He had been commissioned by electric companies to create maximum light from lightbulbs with minimum energy. The problem had been stated by Kirchhoff in 1859: "how does the intensity of the electromagnetic radiation emitted by a black body (a perfect absorber, also known as a cavity radiator) depend on the frequency of the radiation (i.e., the color of the light) and the temperature of the body?". The question had been explored experimentally, but no theoretical treatment agreed with experimental values. Wilhelm Wien proposed Wien's law, which correctly predicted the behaviour at high frequencies, but failed at low frequencies. The Rayleigh–Jeans law, another approach to the problem, created what was later known as the "ultraviolet catastrophe", but contrary to many textbooks this was not a motivation for Planck.

Planck's first proposed solution to the problem in 1899 followed from what Planck called the "principle of elementary disorder", which allowed him to derive Wien's law from a number of assumptions about the entropy of an ideal oscillator, creating what was referred-to as the Wien–Planck law. Soon it was found that experimental evidence did not confirm the new law at all, to Planck's frustration. Planck revised his approach, deriving the first version of the famous Planck black-body radiation law, which described the experimentally observed black-body spectrum well. It was first proposed in a meeting of the DPG on October 19, 1900 and published in 1901. This first derivation did not include energy quantization, and did not use statistical mechanics, to which he held an aversion. In November 1900, Planck revised this first approach, relying on Boltzmann's statistical interpretation of the second law of thermodynamics as a way of gaining a more fundamental understanding of the principles behind his radiation law. As Planck was deeply suspicious of the philosophical and physical implications of such an interpretation of Boltzmann's approach, his recourse to them was, as he later put it, "an act of despair ... I was ready to sacrifice any of my previous convictions about physics."

The central assumption behind his new derivation, presented to the DPG on 14 December 1900, was the supposition, now known as the Planck postulate, that electromagnetic energy could be emitted only in quantized form, in other words, the energy could only be a multiple of an elementary unit E = h \nu, where h is Planck's constant, also known as Planck's action quantum (introduced already in 1899), and \nu (the Greek letter nu, not the Roman letter v) is the frequency of the radiation. Note that the elementary units of energy discussed here are represented by h \nu and not simply by h. Physicists now call these quanta photons, and a photon of frequency \nu will have its own specific and unique energy. The amplitude of energy at that frequency is then a function of the number of photons of that frequency being produced per unit of time.

At first Planck considered that quantization was only "a purely formal assumption ... actually I did not think much about it..."; nowadays this assumption, incompatible with classical physics, is regarded as the birth of quantum physics and the greatest intellectual accomplishment of Planck's career (Ludwig Boltzmann had been discussing in a theoretical paper in 1877 the possibility that the energy states of a physical system could be discrete).


In 1905, Einstein recognized that Planck's proposal of light quantization was key to understanding the photoelectric effect and wrote a paper of the subject, one of four discoveries published that year, now referred to as the Annus Mirabilis papers.

From Wikipedia:

The Annus Mirabilis papers are four articles pertaining to the photoelectric effect (which gave rise to quantum theory), Brownian motion, the special theory of relativity, and E = mc2 that Albert Einstein published in the Annalen der Physik scientific journal in 1905. These four works contributed substantially to the foundation of modern physics and changed views on space, time, and matter.


The first of these papers was entitled On a Heuristic Viewpoint Concerning the Production and Transformation of Light. The ideas proposed in the paper resolved an unsolved puzzle by suggesting that energy is exchanged only in discrete amounts (quanta). This idea was pivotal to the early development of quantum theory.

Many great scientists stood, and still stand, on the shoulders of Planck and Einstein in developing the theoretical and observational basis of quantum mechanics.

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Response to DreamGypsy (Reply #36)

Wed Feb 13, 2013, 03:33 PM

38. You are really enjoying yourself...

I love it! I also have a series of lectures on Einstein's theories...I have let my continuing education lapse...but so rarely do I find anybody with any interest in discussing any of this.

You'll think I'm as mad as the Hatter but Einstein's theory of special relativity ...that matter and energy are constant and that matter is never destroyed, merely converted to energy, and Lavoisier's principle of mass conservation, saved my sanity when my daughter died 3 years ago. It made infinity more sense than some notion that she had gone to some 'after-life'

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Response to Sekhmets Daughter (Reply #22)

Wed Feb 13, 2013, 01:40 PM

26. lol....believe me, I'm not studying it, I would just like to be

conversational about it.

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Response to clarice (Reply #26)

Wed Feb 13, 2013, 01:59 PM

28. Ckarice, you're too cute...

You know many people who sit around talking Quantum Mechanics? I'm teasing, I am always curious myself and I wish I knew more people who could/would talk about physics.

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Response to Sekhmets Daughter (Reply #28)

Wed Feb 13, 2013, 02:21 PM

29. You know many people who sit around talking Quantum Mechanics?

No, but I love being a smarty pants !

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Response to clarice (Reply #29)

Wed Feb 13, 2013, 02:24 PM

30. Welcome to DU

where smarty pants abound!

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Response to Sekhmets Daughter (Reply #30)

Wed Feb 13, 2013, 02:48 PM

33. Thanks.....you ROCK !!!

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Response to clarice (Original post)

Wed Feb 13, 2013, 12:58 PM

13. Some very important knowledge about the cosmos is based on information ~13.5 billion years old.

The cosmic background microwave radiation.

Hubble found galaxies for us that formed a few hundred years after the big bang. Many of the stars in those galaxies burned out, were novas, or supernovas long, long ago. The galaxies may have collapsed, merged, or been pulled apart. Giant hamsters are improbable, but...

I think it's wonderful that we get to experience directly the 4-dimensional macro universe this way.

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Response to clarice (Original post)

Wed Feb 13, 2013, 01:05 PM

14. Aw heck...just hop through a worm hole and travel a million light years in a sec and take a look...

or make an entanglement camera and see what that star of yours is doing today!

I don't have a clue about mirror symmetry, but if you keep hanging around Brian Greene, the only certain thing is that eventually you're gonna get more confused.

See ya in the next dimension!

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Response to Sancho (Reply #14)

Wed Feb 13, 2013, 01:15 PM

18. lol....and what's funny is...

Mr. Greene is trying to explain this stuff in layman's terms.

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Response to clarice (Original post)

Wed Feb 13, 2013, 01:09 PM

16. Try figuring out quantum entanglement...so cool.

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Response to clarice (Original post)

Wed Feb 13, 2013, 01:32 PM

23. Considering a star, like our sun, has a lifespan of 8 billion years

1 million is not a lot of time.

To put it in human terms, if your lifespan was 75 years, that 1 million years would be like looking in on you, as a human, on a Tuesday, and then seeing you again on a Friday.

How much would you have changed in three days?

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Response to Confusious (Reply #23)

Wed Feb 13, 2013, 01:37 PM

25. Yes, I used 1 million as a conversation starter.

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