A few questions for physicists

[Quackers]

Btw, a huge physics story is blowing up. The BBC article states it's in noble prize territory.

 

[BenitoChavez]

Btw, a huge physics story is blowing up. The BBC article states it's in noble prize territory.

Interesting. If it holds up, its another reason why the big bang should still be taught

 

[Leoreth]

Btw, a huge physics story is blowing up. The BBC article states it's in noble prize territory.

Which Nobel prize though?

 

[peter grimes]

"I can't tell you how exciting this is," said Dr Jo Dunkley, who has been searching through data from the European Planck space telescope for a B-mode signal.

"Inflation sounds like a crazy idea, but everything that is important, everything we see today - the galaxies, the stars, the planets - was imprinted at that moment, in less than a trillionth of a second. If this is confirmed, it's huge."

Source: http://www.bbc.com/news/science-environment-26605974

I can hear the religionists checking their holy creation stories now...

Daily News Headline:
"Scientists See God's Fingerprint On Early Universe!"

Sometimes I wish people were more careful with their words, but then I realize that at some point you can't be held responsible for how other people misconstrue your words.

 

[timtofly]

It was imprinted, is not the issue. How it developed is.

 

[Ghpstage]

I don't think the Earth does rotate in relation to space. It does according to Newtonian absolute space, of course. But I think Einstein, and no doubt someone else before him, debunked the idea of absolute space.

The Earth rotates in relation to other "objects" in the cosmos.

Still, maybe you're right. Maybe it would be possible to detect the Earth's rotation even if it were the only object in the Universe. There's surely a measurable difference in effect between the poles and the equator.

Gigaz posted the way it was eventually proven, but in its abscence there are many things that could be used to show the rotation, such as the existance of the jet stream, the shape of the Earth, weather undergoing the Coriolis effect, the posiblity of geosynchronous orbits and more.
However, I don't think that any of these help show if motion is actually 'relative' to space in any way, as they all depend on a Earth rotating relative to its own axis.

This might be more up your alley. Its a testable prediction made by general relativity that relates to a rotating mass 'dragging' space in its wake, not yet been defacto detected but it shouldn't be long now.

 

[tokala]

Some articles on the detection of the influence of cosmological inflation on the microwave background:

Basic Level

Intermediate

The paper itself

This is indeed a big one.

 

[warpus]

I was under the impression that there was disagreement over the whole "is the Earth spinning relative to 'space' or not?" thing? I mean, Einstein showed up to the scene by slamming his fist on the table and proclaiming that everything is relative to everything else and that objective aether doesn't exist. But then I remember reading multiple times that the Earth produces many effects that could only happen if it was spinning.

 

[Mise]

Intermediate

So, have I got this correct? I got a bit lost about half way along but hopefully I got the gist??? (Directed at anyone with an understanding of this stuff, not just tokala!)

1) We know that the universe is basically uniform
2) One theory that explains this uniformity is "inflation". That's the conventional theory, anyway - we don't really know for sure, and inflation has a number of problems, but that's the theory we've gone with so far.
3) We don't know anything about what happened during the inflationary era (~10^-35s after the big bang)
4) If inflation happened perfectly, the Cosmic Microwave Background (CMB) would be uniform
5) The CMB is not uniform; there are perturbations during the inflationary era that result in slight temperature changes
6) These slight differences are what eventually became stars (or areas where there aren't any stars I guess)
7) The perturbations during the inflationary era result in polarisation of the CMB, which we can detect
8) There are two types of perturbation that happened in the inflationary era: density perturbations, and gravitational-wave perturbations. Both types cause polarisation in the CMB.
9) These can be separated from one another experimentally, because density-induced polarisation is only ever E-mode, whereas graviton-induced polarisation is both E- and B-mode
10) We've done that, and we know that density-induced polarisation is a thing
11) However, B-mode polarisation can also be caused by other things, such as gravitational lensing
12) Presumably, separating out B-mode polarisation that is caused by gravitational lensing from B-mode polarisation that is caused by gravitons during the inflationary era is really hard, which is why this is such a big deal
13) BICEP2 has done that now, so yeah, we know something important about the inflationary era. BUT WHAT?!
14) Energy scale! That's an important physics thing, because it tells us ________ <someone fill in the planck blank please!>. It's some important property of the inflationary era; it tells us something about the conditions in the inflationary era. I don't know what exactly.
15) But how does it tell us that, and why didn't the density-induced polarisation tell us?
16) Well, density perturbations are functionally related to the energy scale, what we detect/measure has unfortunately gone through another unknown potential function, V(phi), first.
17) We can guesstimate what the energy scale is from the density perturbations, but we don't know exactly, because of that infernal unknown potential function V(phi)
18) OTOH, the gravitational-wave perturbations are a direct function of the energy scale: when we measure the perturbations, we're measuring the energy scale without any darned unknown potential function getting in the way
19) Apparently, perturbations can be described by two numbers, r and n
20) There's a region in which values for r and n make sense, given what we know already
21) Oddly, the only way BICEP2 could get a strong enough reading is if r is some distance outside of this region
22) However, that's not a problem because the error margins on what we know already are probably high enough to accommodate BICEP2
23) Turns out that BICEP2 reported an r of 0.20 (between 0.15 and 0.27 in standard errors)
24) All of this suggests that the Energy Scale during inflation was really big
25) It's so big, in fact, that a bunch of theories probably don't work anymore
26) There are ways around it, but such a large Energy Scale is "provocative"
27) Anyway, models can be adjusted. The really important thing is that inflation is definitely a real thing that exists (well, assuming the experiment holds water)



Things that I need clarifying for me:
A) How does the uncertainty principle figure into this? The line went that the HUP and quantum fluctuations etc resulted in divergence from a completely uniform universe. But how does this fit in with the gravitational waves causing divergence from a completely uniform universe? Is it simply that HUP results in density perturbations?
B) Why is the Energy Scale thing an important quantity? What is the significance of 10^15 GeV vs 10^2 GeV or whatever? What difference does all that make?

 

[Borachio]

Oh this has been done long ago.
http://en.wikipedia.org/wiki/Foucault_pendulum

Yes I know about Foucault's pendulum. It suddenly resurfaced in my mind as I was posting.

Nevertheless, all that tells us is that points, other than the very poles, on the surface of the Earth are rotating round an axis. Which is my point: that in the absence of any reference points there's no reason to think there's any movement.

 

[Quackers]

Physics stories in the news are impossible to dispense to the layman. You simply cannot do it justice. It is a futile endeavour.

You need to sit down open a textbook and get going for a few hundred hours to be able to "think" you understand it. Just my two quacks.

 

[Borachio]

I'm inclined to agree.

I don't know though.

Maybe the general public (I include myself in this august body) needs to be informed about these things. Even if people can't understand it all.

Maybe it stimulates the collective imagination.

Maybe the taxpayer needs reassurance that all these millions are actually being spent on... something.

Maybe, bit by bit, the general public will eventually understand it all.

 

[Ghpstage]

So, have I got this correct? I got a bit lost about half way along but hopefully I got the gist??? (Directed at anyone with an understanding of this stuff, not just tokala!)
.......
Things that I need clarifying for me:
A) How does the uncertainty principle figure into this? The line went that the HUP and quantum fluctuations etc resulted in divergence from a completely uniform universe. But how does this fit in with the gravitational waves causing divergence from a completely uniform universe? Is it simply that HUP results in density perturbations?
B) Why is the Energy Scale thing an important quantity? What is the significance of 10^15 GeV vs 10^2 GeV or whatever? What difference does all that make?

Even after reading a few short books on QM stuff its still more or ess completely incomprehensible.

1) I'd like to know this too, especially the HUP part as I thought that only set limits on the ability of an observer to make meusurements accurately. .
I would have thought the density changes would occur purely on the back of the random motions at the quantum scale.
2) I know at the Planck scale (10^19GeV), known physics goes out the window and we have no hope of making useful predictions without at least a working theory of Quantum Gravity. My naive guess would be that the energy scale is important due to its impact on the interactions between subatmoic particles, photons etc. e.g. electron synthesis fro photon collisions will require energy scales above a certain point, while quarks will only bind to form protons and neutrons below a certain point (maybe between points).

 

[FredLC]

I was under the impression that there was disagreement over the whole "is the Earth spinning relative to 'space' or not?" thing? I mean, Einstein showed up to the scene by slamming his fist on the table and proclaiming that everything is relative to everything else and that objective aether doesn't exist. But then I remember reading multiple times that the Earth produces many effects that could only happen if it was spinning.

There are issues, yes.

Though it's true that the idea of space being an absolute you can compared to is indeed debunked, it's very feasible that space-time does have that quality. In fact, it can even be soundly structured, as a gigantic membrane (or simply "brane") suggests in M-theory.

For a laymen knowledge of the issue, I suggest Brian Greene's "The Fabric of the Cosmos".

Regards .


Sent from my iPad using Tapatalk

 

[El_Machinae]

It&#8217;s the inflaton that eventually converts into matter and radiation, so the inflaton fluctuations produce fluctuations in the density of the early plasma

I didn't know that! I always thought that the inflationary effect was exogenous to the 'stuff' that eventually became matter/energy.

 

[tokala]

So, have I got this correct? I got a bit lost about half way along but hopefully I got the gist??? (Directed at anyone with an understanding of this stuff, not just tokala!)

Uh,oh, I was hoping someone with a more in-depth knowledge of either cosmology or particle physics would jump in here.
My knowledge of that stuff is a decade or so out of date, and wasn't that deep at the time either

Nevertheless, I will try my best.

1) We know that the universe is basically uniform
2) One theory that explains this uniformity is "inflation". That's the conventional theory, anyway - we don't really know for sure, and inflation has a number of problems, but that's the theory we've gone with so far.

3) We don't know anything about what happened during the inflationary era (~10^-35s after the big bang)

Until now Previously, our earliest knowledge was based on the ratio of the amounts of the lightest elements in the universe, which allowed some insights into the conditions some 1 second after the Big Bang. Now we jumped ahead by some 30 orders of magnitude with our limits of knowledge.

4) If inflation happened perfectly, the Cosmic Microwave Background (CMB) would be uniform

Not completely, any unisotropy just would have been diluted so far to be pretty much undetectable.

5) The CMB is not uniform; there are perturbations during the inflationary era that result in slight temperature changes

6) These slight differences are what eventually became stars (or areas where there aren't any stars I guess)

In principle yes, but at least when I was still actively following that stuff, it was supposed to be a top down process galaxy clusters-->galaxies-->stars

7) The perturbations during the inflationary era result in polarisation of the CMB, which we can detect
8) There are two types of perturbation that happened in the inflationary era: density perturbations, and gravitational-wave perturbations. Both types cause polarisation in the CMB.

Now we are getting in the territory where I'm not comfortable any more, either.
There is a principle problem that the CMB represents the conditions of the universe at the point in time when enough of the primordial plasma had "re"combined to atoms, and became transparent to electromagnetic radiation, which was some 3x10^6 years after the Big Bang.
Any pertubations during the inflation era can only indirectly result in specific polarisation patterns, due to their remanent effects on the structure of the universe those 3x10^6 years later.
And if I understand that blog post correctly, those density pertubations from inflation are themselve only an indicator of pertubations of those unknown "inflaton" field that drove the inflation, and decayed into matter and radiation at the end of the inflation era.

9) These can be separated from one another experimentally, because density-induced polarisation is only ever E-mode, whereas graviton-induced polarisation is both E- and B-mode
10) We've done that, and we know that density-induced polarisation is a thing
11) However, B-mode polarisation can also be caused by other things, such as gravitational lensing

12) Presumably, separating out B-mode polarisation that is caused by gravitational lensing from B-mode polarisation that is caused by gravitons during the inflationary era is really hard, which is why this is such a big deal
13) BICEP2 has done that now, so yeah, we know something important about the inflationary era. BUT WHAT?!

The big deal is rather that cosmological inflation was "only" a compelling theorical construct up to this point in time, with only very, very indirect support in actual measurements. And now for the first time we have a fairly straightforward experimental confirmation.
Not only that inflation happened, but that the conditions during that time were indeed in the same ballpark as expected by theory, if a bit on the high (energetic) side.
Add to that that already mentioned huge jump in our temporal limits of knowledge, and the apparent fact that this also enables as to get very close to the energy threshold for unification of the 3 non-gravity fundamental forces, and this discovery is rightfully described as only ranking third in importance in astrophysics behind the (hypothetical) detection of life on other planets or finding a major component of Dark Matter.

14) Energy scale! That's an important physics thing, because it tells us ________ <someone fill in the planck blank please!>. It's some important property of the inflationary era; it tells us something about the conditions in the inflationary era. I don't know what exactly.

This might actually have been a red herring, as apparently the paper didn't mention energy scale apart from the introduction. It is mentioned however, that conclusions in regard of the energy scale require large angle measurements, and the field scanned by BICEPS was some 20x50°, which might have been not enough for that purpose.
The Planck space telescope however was doing all-sky measurements, and there might be some results in the pipeline.

Apart from that, I'm as clueless as you

15) But how does it tell us that, and why didn't the density-induced polarisation tell us?
16) Well, density perturbations are functionally related to the energy scale, what we detect/measure has unfortunately gone through another unknown potential function, V(phi), first.
17) We can guesstimate what the energy scale is from the density perturbations, but we don't know exactly, because of that infernal unknown potential function V(phi)
18) OTOH, the gravitational-wave perturbations are a direct function of the energy scale: when we measure the perturbations, we're measuring the energy scale without any darned unknown potential function getting in the way
19) Apparently, perturbations can be described by two numbers, r and n
20) There's a region in which values for r and n make sense, given what we know already
21) Oddly, the only way BICEP2 could get a strong enough reading is if r is some distance outside of this region
22) However, that's not a problem because the error margins on what we know already are probably high enough to accommodate BICEP2
23) Turns out that BICEP2 reported an r of 0.20 (between 0.15 and 0.27 in standard errors)
24) All of this suggests that the Energy Scale during inflation was really big
25) It's so big, in fact, that a bunch of theories probably don't work anymore
26) There are ways around it, but such a large Energy Scale is "provocative"

Sounds right, as far as I can tell

27) Anyway, models can be adjusted. The really important thing is that inflation is definitely a real thing that exists (well, assuming the experiment holds water)

Indeed.

Things that I need clarifying for me:
A) How does the uncertainty principle figure into this? The line went that the HUP and quantum fluctuations etc resulted in divergence from a completely uniform universe. But how does this fit in with the gravitational waves causing divergence from a completely uniform universe? Is it simply that HUP results in density perturbations?
B) Why is the Energy Scale thing an important quantity? What is the significance of 10^15 GeV vs 10^2 GeV or whatever? What difference does all that make?

Even after reading a few short books on QM stuff its still more or ess completely incomprehensible.

1) I'd like to know this too, especially the HUP part as I thought that only set limits on the ability of an observer to make meusurements accurately. .
I would have thought the density changes would occur purely on the back of the random motions at the quantum scale.
2) I know at the Planck scale (10^19GeV), known physics goes out the window and we have no hope of making useful predictions without at least a working theory of Quantum Gravity. My naive guess would be that the energy scale is important due to its impact on the interactions between subatmoic particles, photons etc. e.g. electron synthesis fro photon collisions will require energy scales above a certain point, while quarks will only bind to form protons and neutrons below a certain point (maybe between points).

Regarding the uncertainty principle, it's not contrained to a human observer. Any measurement instrument, of for that matter, any interaction of a quantum system with the outside world that constrains it state will be equivalent with an "observation".

And even in a hypothetical empty universe of 0K temperature, there would be still quantum fluctuations, for example creating virtual particles that will disappear again within inconceivably short time scales.

In quantum mechanics there are several pairs of complementary observables, the best known are time and energy, and momentum and location, the latter featuring in the the HUP.
The product of those observables the uncertainties of those obsevables cannot be determined more precise than the Planck constant, and even in the absence of an observers a system that has a very high energy scale will also have a very short timescale, for example.

I'm not sure how this precisely translates into the impossibility of a exactly uniform early universe, but this might make it more plausible, at least.


Regarding the energy scale, here too I'm out of my depth, but as mentioned 10^16 GeV is the energy scale where the unification of the three non-gravity forces is expected, and 10^19 GeV of all fundamental forces.

Those energy scales are way, WAY beyond anything humans will ever be able to access, so the only hope of experimental data around these regimes is finding stuff nature provides.

It's intriguing that the energy scale of the inflation era might actually be in that regime, and (I speculate here) there might be an actual functional relationship between the inflation mechanism and those force unifications, opening up the possibility to approach a real "theory of everything" tying up anything from the largest scale cosmology to the smallest subatomic particles, as well as the forces that make them interact.

 

[Mise]

Thanks Tokala!

 

[warpus]

For a laymen knowledge of the issue, I suggest Brian Greene's "The Fabric of the Cosmos".

Excellent book, I have it sitting on my bookcase in my office at home

 

[dutchfire]

So, have I got this correct? I got a bit lost about half way along but hopefully I got the gist??? (Directed at anyone with an understanding of this stuff, not just tokala!)
Things that I need clarifying for me:
A) How does the uncertainty principle figure into this? The line went that the HUP and quantum fluctuations etc resulted in divergence from a completely uniform universe. But how does this fit in with the gravitational waves causing divergence from a completely uniform universe? Is it simply that HUP results in density perturbations?
B) Why is the Energy Scale thing an important quantity? What is the significance of 10^15 GeV vs 10^2 GeV or whatever? What difference does all that make?

I'll give it a try, though cosmology is not my field of expertise.

6) These slight differences are what eventually became stars (or areas where there aren't any stars I guess)

As tokala mentioned, the length scale of these fluctuations is much bigger than stars.

14) Energy scale! That's an important physics thing, because it tells us ________ <someone fill in the planck blank please!>. It's some important property of the inflationary era; it tells us something about the conditions in the inflationary era. I don't know what exactly.

Energies scales are very important throughout physics, since they indicate what kind of physics/effects are likely involved.
If someone asks you to build something collision proof, then you want to know if he's talking about collisions with a tennis ball, or with a train. This is the 'energy scale' of the collision.

9) These can be separated from one another experimentally, because density-induced polarisation is only ever E-mode, whereas graviton-induced polarisation is both E- and B-mode
10) We've done that, and we know that density-induced polarisation is a thing
11) However, B-mode polarisation can also be caused by other things, such as gravitational lensing
12) Presumably, separating out B-mode polarisation that is caused by gravitational lensing from B-mode polarisation that is caused by gravitons during the inflationary era is really hard, which is why this is such a big deal

I think this part of the original article explains some things quite well (got mangled by the copy-paste though ):

Gravitational lensing of the CMB’s light by large scale
structure at relatively late times produces small deflections of
the primordial pattern, converting a small portion of E-mode power into B-modes. The lensing B-mode spectrum is similar to a smoothed version of the E-mode spectrum but a factor 100 lower in power, and hence also rises toward sub-degree
scales and peaks around 1000. The inflationary gravitational wave (IGW) B-mode, however, is predicted to peak at multipole 80 and this creates an opportunity to search for it around this scale where it is quite distinct from the lensing

Basically, the CMB radiation was originally mostly in E mode. But this radiation was emitted long ago and has since interacted with gravitational waves, which has caused some of the E modes to become B modes. We expect these transformed modes to have the same general properties as the E modes, in particular L is approximately 1000.

The original CMB also contained some B modes though, with L approximately 80. So by looking at L=80, we're likely to see these original B modes (IGW), if they exist.
This research has found strong modes between L=50 and L=150, so these are probably the IGW.


Side note: the L here is like a (spherical) Fourier mode, so L=0 corresponds to something which is the same in all directions of the sky, L=1 is bigger on one side of the sky and smaller on the other side, and the higher L correspond to even higher overtones (so shorter length scales on the visible sky).

 

[Mise]

Thanks df!