Difficult Concepts (for me)

[notFritzArgelander]

thank you Mark.

thank you so much again nFA.
I remember reading that a reason why its called dark, is because of how little we know about
dark energy. we're in the dark about it. and dark matter too.

nFA,
I was just wondering:
what would have Aristotle have thought about all of this that we talked about in this thread?
how about Newton?
and Einstein? how much of this did Einstein know?
some, all?
would would Hawking have thought?
would he have agreed?
how about Leonard Susskind, or Kip Thorne?

You know I was going to take this very seriously and answer something based on how different philosophies in the foundations of mathematics treat infinities...... The folks above had VERY different ideas about infinity. But then when you mentioned....

or Alyssa Milano, or Scarjo?
hahahaha

I decided to watch a movie or two... Perhaps another time...

[chasmanian]

ok. lol

in the meantime, I am now writing a screenplay for a guaranteed to be blockbuster film,
celebrating the contributions of 2 women to science. (side note, they both died when they were 53.)

the first is Emmy Noether.

from the wiki:
https://en.wikipedia.org/wiki/Emmy_Noether

"She was described by Pavel Alexandrov, Albert Einstein, Jean Dieudonné, Hermann Weyl and Norbert Wiener as the most important woman in the history of mathematics."

the other is Henrietta Swan Leavitt. (no relation to Leavitt to Beaver of which I'm aware.
perhaps in some alternate universe there's a tv show called Leavitt to Swan?).
from the wiki:
https://en.wikipedia.org/wiki/Henrietta ... fic_impact

"The accomplishments of Edwin Hubble, the American astronomer who established that the universe is expanding, also were made possible by Leavitt's groundbreaking research."

ok, now if ONLY I could think of 2 hollywood actresses to play the parts of these 2 women scientists.
by Jove, I think I've got it!!
Alyssa Milano and Scarjo?

[AntennaGuy]

"Alyssa Milano and Scarjo?" Well, I had to look up "Scarjo," since I had never heard of that name. Scarface maybe, but not Scarjo.
And the winner is... Scarlett Johansson. Sigh. Really? Now that's some brain cells that I could have used for more useful knowledge, but which will now be devoted to "Scarjo."

[notFritzArgelander]

"Alyssa Milano and Scarjo?" Well, I had to look up "Scarjo," since I had never heard of that name. Scarface maybe, but not Scarjo.
And the winner is... Scarlett Johansson. Sigh. Really? Now that's some brain cells that I could have used for more useful knowledge, but which will now be devoted to "Scarjo."

Gee whizzacres! Don't confuse Scarjo with the Kardashians! She can actually DO THINGS!

[AntennaGuy]

"Alyssa Milano and Scarjo?" Well, I had to look up "Scarjo," since I had never heard of that name. Scarface maybe, but not Scarjo.
And the winner is... Scarlett Johansson. Sigh. Really? Now that's some brain cells that I could have used for more useful knowledge, but which will now be devoted to "Scarjo."

Gee whizzacres! Don't confuse Scarjo with the Kardashians! She can actually DO THINGS!

Yes, I understand that she can. But these nicknames are silly. Wouldn't you agree, uh... Fritz-ay ? (That has kind of a ring to it. For example, "Et tu, Fritz-ay?") Eway allway ovelay Fritz-ay!

[notFritzArgelander]

"Alyssa Milano and Scarjo?" Well, I had to look up "Scarjo," since I had never heard of that name. Scarface maybe, but not Scarjo.
And the winner is... Scarlett Johansson. Sigh. Really? Now that's some brain cells that I could have used for more useful knowledge, but which will now be devoted to "Scarjo."

Gee whizzacres! Don't confuse Scarjo with the Kardashians! She can actually DO THINGS!

Yes, I understand that she can. But these nicknames are silly. Wouldn't you agree, uh... Fritz-ay ? (That has kind of a ring to it. For example, "Et tu, Fritz-ay?") Eway allway ovelay Fritz-ay!

I’ve given up fighting the trend. I confess to being confused by JLo and LiLo. (Is she still alive? No need to answer the question. It’s rhetorical.) I quickly surrendered to the human tendency to adopt portmanteau contractions. As for your Fritzay.... I’ve been called worse with more ill will so I’ll take it easy but take it, as Studs would say.

[chasmanian]

I emailed the Q and A youtube Professor Chris Impey, and asked him for his thoughts about this stuff.
he replied in a very kind manner,
and suggested I check out some forums, like physicsforums.com.


so, I started a thread there.
here's a link to it, for anyone who's interested.
and I would like to add that,
I now have even more appreciation for nFA.
thank you again nFA for your incredible generosity,
explaining so much cool amazing fascinating stuff to us,
and for your kindness.

https://www.physicsforums.com/threads/t ... es.991285/

[chasmanian]

nFA, have been wondering about this a bit.

at the other forum, a member replied to a question.
he quoted me piecemeal, and replied to each piece.
I am doing my best to present it clearly here.
if this is too confusing, (and I totally understand if so),
please just scroll to the bottom of my post here.
I will write my question again.
thank you.

me: "how does and how will the expansion of the Universe affect this?"

other forum dude: "depends on what you are referring to by "this". Your question is very poorly stated."

me: "the ones that overlap and intersect with each other now, will continue to do so."

other forum dude: "no. Their centers are receding from each other way faster than their radii are increasing (*)"

me: "and the ones that do not overlap and intersect, will continue to stay separate from each other."

other forum dude: "yes"

*EDIT: my statement is not valid if the two observable universes are within a galactic cluster, since things the size of clusters and smaller do not recede from each other

ok, here is what I'm wondering about:
the other forum member said that the centers of the observable universes are receding from each other,
way faster than their radii are increasing.

is he right, or does it depend on what Dark Energy does?

[notFritzArgelander]

nFA, have been wondering about this a bit.

at the other forum, a member replied to a question.
he quoted me piecemeal, and replied to each piece.
I am doing my best to present it clearly here.
if this is too confusing, (and I totally understand if so),
please just scroll to the bottom of my post here.
I will write my question again.
thank you.

me: "how does and how will the expansion of the Universe affect this?"

other forum dude: "depends on what you are referring to by "this". Your question is very poorly stated."

me: "the ones that overlap and intersect with each other now, will continue to do so."

other forum dude: "no. Their centers are receding from each other way faster than their radii are increasing (*)"

me: "and the ones that do not overlap and intersect, will continue to stay separate from each other."

other forum dude: "yes"

*EDIT: my statement is not valid if the two observable universes are within a galactic cluster, since things the size of clusters and smaller do not recede from each other

ok, here is what I'm wondering about:
the other forum member said that the centers of the observable universes are receding from each other,
way faster than their radii are increasing.

is he right, or does it depend on what Dark Energy does?

it depends on a lot of things, actually. it's impossible to say that he is right or wrong in all cases because it depends on how you are placing "centers of observable universes" just as much as it depends on what Dark Energy is doing.

assume we are talking about a placement of "observable universes" that are not intersecting now but are barely touching NOW in the universe at 13.8 Billion years of look back time. in another billion years (or any additional time, actually) the observable universes will intersect and share some of the same space available for observation. so for nearest neighbor observable universes they eventually overlap. because of the accelerating expansion of the universe there will be more distant "observable universes" which will never overlap in that way. that is what your interlocutor is talking about and that is the subset of "observable universes" for which the statement is true. it is not true for all. it is obviously false for nearest neighbor bubbles.

[chasmanian]

ok, thank you very much nFA.
you're awesome!!
so very fascinating.

[notFritzArgelander]

ok, thank you very much nFA.
you're awesome!!
so very fascinating.

Here is a link that discusses the math of it. At present objects 46 B lyr away are within the 13.8 B yr look back time. In the future we will be able to see objects now 61 B lyr away at the maximum. It is only beyond that present distance that the universe is forever unseeable due to acceleration from Dark Energy.

https://www.forbes.com/sites/startswith ... 2cc664f827

[helicon]

Very interesting thread...

[chasmanian]

thank you nFA.

I wonder what Ethan would think about this thread.

[turboscrew]

I also find this thread very interesting.
I think, to science there is no unobservable universe - because we can't observe it.
Science is models. "The real truth" is more or less religion.
Also, I've got this funny idea that if you travel in speed of light, you wouldn't notice. Everything would look normal to you. Just the time and spatial dilatations make everything look normal to you.

I may be totally wrong, though.

[notFritzArgelander]

I also find this thread very interesting.
I think, to science there is no unobservable universe - because we can't observe it.
Science is models. "The real truth" is more or less religion.
Also, I've got this funny idea that if you travel in speed of light, you wouldn't notice. Everything would look normal to you. Just the time and spatial dilatations make everything look normal to you.

I may be totally wrong, though.

The consequences of the unobservable portions of the universe, have observable consequences, though. For instance we can never observe (because of Dark Energy and the accelerating expansion of the universe) all of the universe even if we wait for an infinite time. Nevertheless the observations we can make are consistent with the universe being flat, homogenous and isotropic. Noether's Theorem guarantees that an infinite, homogenous, isotropic universe (no need for flatness, yet) has momentum and angular momentum conservation. So every experiment that we do (and there are a lot of them) where momentum and angular momentum are conserved is in accord with there being parts of the universe that we can never see. Flatness guarantees zero average energy density and so infinite extent and energy conservation.

Science constructs models that explain the observations. It is rather rigorous in that a compelling contradiction to a theory chucks the theory out and demands a replacement. That, I think, is as close to "the real truth" as one can get. I don't think that "The Real Truth" is knowable. Others might differ. But I think Platonism (knowing The Real Truth) has been dead since the 14th century. YMMV.

As you approach light speed the appearances of objects become increasingly distorted. MIT had a neat game to play online that illustrated the distortion of optics caused by relativistic motion. I've tried to find it again but failed. Instead this 6 minute YouTube clip shows the same effects.



There are several different ways in which relativity distorts appearances and the video starts out simple and then adds each effect in turn.

[notFritzArgelander]

PS On the optical effects of Special Relativity, the Doppler Effect is somewhat familiar as is the "aberration" effect (the distortion that comes from moving through the rain of photons). The "aberration" is somewhat analogous to when running through vertically falling raindrops your front gets wetter than your back.

Less familiar is what the computer generated narrator refers to as the Terrell rotation effect. It's been known for over 60 years but there is a short summary and a neat graphic here: https://en.wikipedia.org/wiki/Terrell_rotation

Edit: There is also a good wikipedia entry on aberration: https://en.wikipedia.org/wiki/Aberration_(astronomy)

[Graeme1858]

Could it be that there are two different things being discussed here. The observable universe exists within an infinite universe and it's not a physical thing but a visual thing constrained by the position of the observer and the finite speed of light. Everyone's observable universe overlaps with everyone else's where ever they are, down the street, 13 billion LYs away 46 billion LYs away or 90 billion LYs away.

Bubbles implies a way of thinking perhaps better described by a multiverse theory. As I understand it, the multiverse comes about due to infinite multiple big bangs forming an infinite number of separate universes which all exist in an infinite universe. Our observable universe exists within our universe which exists within our bubble which exists with many others in the multiverse. I once read that the cold spot on the CMB was an indication of an adjacent universe in contact with ours which exists at a colder temperature than ours. But I don't think many people went for it. Not something we will ever be able to prove anyway.

Sorry if I'm rambling nonsense, I've just got up!

Great thread!

Cheers

Graeme

[notFritzArgelander]

A welcome ramble.

It’s true that the multiverse folks speak of bubbles but I’m understanding chasmanian’s bubbles as different. Different bubble for each observer, no multiverses implied, unless I’m mistaken. Multiverses toss out Noether’s Theorem and are repugnant.

I need to clarify that as in the link in post #31 that points further than 61 billion light years away now can never see each other due to accelerating expansion. So in our seemingly infinite universe there are observable universes that will never overlap.

That cold spot in the CMB could still be a mere statistically insignificant fluke.

[turboscrew]

I also find this thread very interesting.
I think, to science there is no unobservable universe - because we can't observe it.
Science is models. "The real truth" is more or less religion.
Also, I've got this funny idea that if you travel in speed of light, you wouldn't notice. Everything would look normal to you. Just the time and spatial dilatations make everything look normal to you.

I may be totally wrong, though.

The consequences of the unobservable portions of the universe, have observable consequences, though. For instance we can never observe (because of Dark Energy and the accelerating expansion of the universe) all of the universe even if we wait for an infinite time. Nevertheless the observations we can make are consistent with the universe being flat, homogenous and isotropic. Noether's Theorem guarantees that an infinite, homogenous, isotropic universe (no need for flatness, yet) has momentum and angular momentum conservation. So every experiment that we do (and there are a lot of them) where momentum and angular momentum are conserved is in accord with there being parts of the universe that we can never see. Flatness guarantees zero average energy density and so infinite extent and energy conservation.

Science constructs models that explain the observations. It is rather rigorous in that a compelling contradiction to a theory chucks the theory out and demands a replacement. That, I think, is as close to "the real truth" as one can get. I don't think that "The Real Truth" is knowable. Others might differ. But I think Platonism (knowing The Real Truth) has been dead since the 14th century. YMMV.

As you approach light speed the appearances of objects become increasingly distorted. MIT had a neat game to play online that illustrated the distortion of optics caused by relativistic motion. I've tried to find it again but failed. Instead this 6 minute YouTube clip shows the same effects.



There are several different ways in which relativity distorts appearances and the video starts out simple and then adds each effect in turn.

But in the "vehicle" you are not moving relative to, everything looks normal?
And is indirectly observable unobservable...?

[turboscrew]

PS On the optical effects of Special Relativity, the Doppler Effect is somewhat familiar as is the "aberration" effect (the distortion that comes from moving through the rain of photons). The "aberration" is somewhat analogous to when running through vertically falling raindrops your front gets wetter than your back.

Less familiar is what the computer generated narrator refers to as the Terrell rotation effect. It's been known for over 60 years but there is a short summary and a neat graphic here: https://en.wikipedia.org/wiki/Terrell_rotation

Edit: There is also a good wikipedia entry on aberration: https://en.wikipedia.org/wiki/Aberration_(astronomy)

The aberration was new to me, but your comparison to moving in a rain made it very understandable.
Sorry for the late response, but my first work day after summer vacation just ended.