### Re: LIGO

```On Sun, Mar 31, 2019 at 5:06 PM Lawrence Crowell <
goldenfieldquaterni...@gmail.com> wrote:

>> Yes but LIGO detects the peak to peak displacement of a wave not its
>> power or energy as cameras and radios do. And that means LIGO's ability to
>> detect wave producing things is reduced with distance much more slowly than
>> with telescopes that deal with electromagnetic waves. Peak-to peak
>> displacement is proportional to the Root Mean Square of the wave and the
>> RMS is proportional to the square root of the power. So if there is 4 times
>> less power in the gravitational wave (because the source is twice as far
>> away) the peak to peak displacement is only reduced by a factor of 2.
>>
>

> I guess you will have to give a reference on this.
>

>From LIGO's website:

https://www.ligo.caltech.edu/page/facts

"*improvements will ultimately make LIGO's interferometers 10 times more
sensitive than their initial incarnation. A 10-fold increase in sensitivity
means that LIGO will be able to detect gravitational waves 10 times farther
away than Initial LIGO, which translates into 'sampling' 1000-times more
volume of space (volume increases with the cube of the distance. So 10
times farther away means 10x10x10=1000 times the volume of space)"*

From:

https://dcc.ligo.org/public//P070082/004/P070082-v4.pdf

"the gravitational wave field strength is proportional to the second time
derivative of the quadrupole moment of the source, and it falls off in
amplitude inversely with distance from the source"

From:

https://archive.briankoberlein.com/2016/02/19/how-close-is-too-close/

*"**The amount of shift caused by a gravitational wave is due to its
amplitude, not its energy. While the energy of gravitational waves follow
the inverse square relation, the amplitude of gravitational waves follows
the inverse distance relation. In other words, if we were half as far away
from the merger we’d have seen four times the energy, but only twice the
shift."*

And note that it is the shift that LIGO detect not energy.

> I can see in one sense what you are saying about RMS, but I don't think
> displacemement.
>

That just means as one leg of LIGO is moved to a maximum distance the other
leg is moved to a minimum distance, and the difference between the maximum
and minimum is what causes interference in the Laser beam that LIGO
detects. Needless to say that is not the way a radio receiver works and is
not way film detects light either.

John K Clark

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### Re: LIGO

```On Sunday, March 31, 2019 at 8:23:02 AM UTC-6, John Clark wrote:
>
> On Sun, Mar 31, 2019 at 8:43 AM Lawrence Crowell  > wrote:
>
>
>> > An antenna or any receiver of electromagnetic waves in effect measures
>> the displacement of electrons or equivalently a current is produced.
>>
>
> A radio receiver detects the power in a AC circuit, and that is the Root
> Mean Square voltage times the Root Mean Square current. Unlike LIGO
> radios don't detect peak to peak values.
>
> > A gravitational wave is measured according to strain, but a strain
>> through distance has an energy content as well.
>>
>
> Yes but LIGO detects the peak to peak displacement of a wave not its power
> or energy as cameras and radios do. And that means LIGO's ability to detect
> wave producing things is reduced with distance much more slowly than with
> telescopes that deal with electromagnetic waves. Peak-to peak displacement
> is proportional to the Root Mean Square of the wave and the RMS is
> proportional to the square root of the power. So if there is 4 times less
> power in the gravitational wave (because the source is twice as far away)
> the peak to peak displacement is only reduced by a factor of 2.
>

I guess you will have to give a reference on this. I looked at some
references and I can't find anything on what you say here:

I can see in one sense what you are saying about RMS, but I don't think
displacemement. There is the quadrupole tensor Q = 3d_id_j - d^2δ_{ij},
where fields are Q_{ij}/r^4. The distance to the source is r and the
distance between the two inspiralling black holes is d. The displacement is
given by the metric g_{ab} = δ_{ab} + h_{ab} for the ++ and xx
polarizations. The ++ polarization metric will be h_{++} = 2d_+^2/r^2, for
r the distance to the source, and the curvature is R_++ = ½h_{++}R =
d_{++}/r^4. The Einstein space criterion the metric proportional to the
Ricci curvature and the metric giving the displacement means the
displacement is ~ 1/r^2.

LC

> > So gravitational waves have intensities that drops with the square of
>> the distance
>
>
> I'm not disputing that, but that fact is not inconsistent with the fact
> that LIGO's ability to detect gravitational wave sources only decreases
> linearly with distance because with LIGO the key thing is peak to peak
> displacement of the wave not its intensity.
>
> John K Clark
>
>
>
>
>>

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### Re: Energy efficiency of different programming languages

```

On Sunday, March 31, 2019 at 11:58:46 AM UTC-5, Bruno Marchal wrote:
>
>
> On 30 Mar 2019, at 07:15, Philip Thrift >
> wrote:
>
>
>
>
> https://thenewstack.io/which-programming-languages-use-the-least-electricity/
>
> Which language one uses makes a physical difference.
>
>
> That is correct, interesting for the application, but not directly
> relevant for the “ontological problem” and the mind-body problem.
>
> Physics is not able to make any prediction without assuming something
> (what exactly) capable of selecting our computation in arithmetic.
> Theologically, it still invoke an ontology, which cannot be done when doing
> science.
>
> The fact that efficient computation “survives”, and non efficient do not,
> requires magic if the environnement does not map the finitely many
> accessible histories at (or below) our substitution level.
>
> A quantum computation does not require any energy, note. And both
> observation, and mechanism seems to force the physical reality into a
> combinatory algebra without Kestrel (Kxy = x, which eliminates the
> information in y), nor Starling S (Sxyz = xz(yz)) nor any duplicator (no
> Mocking Bird like M, Mx = xx). Information cannot be physically created,
> nor eliminated, nor duplicated.
>
> We can still have Turing universality without eliminators. Yet we lost
> Turing universality when we have no eliminators and no duplicators, but we
> can regain it with adding “measurement” modal operator (internally defined,
> or not). That is the combinatory BCI algebra, with a core physics where
> energy is a constant, and computations use no energy, yet relative
> subcomputation are allowed to make relative measurement, leading to
> apparent (indexical) breaking of the core laws, and apparent elimination of
> “memories”. There are Turing universal group and group have natural mesure
> theory associated with them, but again, such group must be justified
> mathematically (and theologically to get the private (first person) parts
> not eliminated).
>
> Thinking of group, I have said that physics is a symphony played by the
> number 0, 1, e, PI, gamma, and with the number 24 has chief orchestra. To
> be honest, my motivation comes more from physics and number theory than
> from Metamathematics (mathematical logic, machine theology), and it makes
> me nervous that the number theorist stumble on the right physics before the
> theologian (leading to an arithmeticalism still capable of eliminating the
> first person for awhile). Here is a nice video where John Baez explains
> well why he likes 24 too, and its main role in String Theory (the Riemann
> related to the Monster Group and Moonshine (where deep relation occurs
> between fundamental physics and number theory).
>
>
> To be sure, my favorite reason to love 24 is more the one related to Hardy
> Rademacher and Ramanujan exact formula for the number of partition of a
> number. That plays also some role in fundamental chemistry and
> classification of “orbitals” (or quantum stationary waves).
>
> Bruno
>
>
>
Every programming language has physical semantics -- which depends on its
material computing substrate -- in addition to (substrate-independent)
denotational and operational semantics . That includes quantum programming
languages, like QASM [ https://arxiv.org/abs/1707.03429 ] (for IBM's Q
computer).

- pt

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### Re: Energy efficiency of different programming languages

```
> On 30 Mar 2019, at 07:15, Philip Thrift  wrote:
>
>
>
> https://thenewstack.io/which-programming-languages-use-the-least-electricity/
>
>
> Which language one uses makes a physical difference.

That is correct, interesting for the application, but not directly relevant for
the “ontological problem” and the mind-body problem.

Physics is not able to make any prediction without assuming something (what
exactly) capable of selecting our computation in arithmetic. Theologically, it
still invoke an ontology, which cannot be done when doing science.

The fact that efficient computation “survives”, and non efficient do not,
requires magic if the environnement does not map the finitely many accessible
histories at (or below) our substitution level.

A quantum computation does not require any energy, note. And both observation,
and mechanism seems to force the physical reality into a combinatory algebra
without Kestrel (Kxy = x, which eliminates the information in y), nor Starling
S (Sxyz = xz(yz)) nor any duplicator (no Mocking Bird like M, Mx = xx).
Information cannot be physically created, nor eliminated, nor duplicated.

We can still have Turing universality without eliminators. Yet we lost Turing
universality when we have no eliminators and no duplicators, but we can regain
it with adding “measurement” modal operator (internally defined, or not). That
is the combinatory BCI algebra, with a core physics where energy is a constant,
and computations use no energy, yet relative subcomputation are allowed to make
relative measurement, leading to apparent (indexical) breaking of the core
laws, and apparent elimination of “memories”. There are Turing universal group
and group have natural mesure theory associated with them, but again, such
group must be justified mathematically (and theologically to get the private
(first person) parts not eliminated).

Thinking of group, I have said that physics is a symphony played by the number
0, 1, e, PI, gamma, and with the number 24 has chief orchestra. To be honest,
my motivation comes more from physics and number theory than from
Metamathematics (mathematical logic, machine theology), and it makes me nervous
that the number theorist stumble on the right physics before the theologian
(leading to an arithmeticalism still capable of eliminating the first person
for awhile). Here is a nice video where John Baez explains well why he likes 24
too, and its main role in String Theory (the Riemann regularisation). I think
and Moonshine (where deep relation occurs between fundamental physics and
number theory).

To be sure, my favorite reason to love 24 is more the one related to Hardy
Rademacher and Ramanujan exact formula for the number of partition of a number.
That plays also some role in fundamental chemistry and classification of
“orbitals” (or quantum stationary waves).

Bruno

>
> - pt
>
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### Dark Matter

```A second galaxy has been found that contains no Dark Matter. These odd
galaxies are about the same size as our Milky Way but contain 200 times
fewer stars. They pretty much rule out the idea that Dark Matter doesn't
exist and our laws of gravity just need to change because unlike every
other galaxy studied these 2 oddballs behave just as Newton says they
should.

Second galaxy without dark matter discovered

John K Clark

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### Re: LIGO

```On Sun, Mar 31, 2019 at 8:43 AM Lawrence Crowell <
goldenfieldquaterni...@gmail.com> wrote:

> > An antenna or any receiver of electromagnetic waves in effect measures
> the displacement of electrons or equivalently a current is produced.
>

A radio receiver detects the power in a AC circuit, and that is the Root
Mean Square voltage times the Root Mean Square current. Unlike LIGO radios
don't detect peak to peak values.

> A gravitational wave is measured according to strain, but a strain
> through distance has an energy content as well.
>

Yes but LIGO detects the peak to peak displacement of a wave not its power
or energy as cameras and radios do. And that means LIGO's ability to detect
wave producing things is reduced with distance much more slowly than with
telescopes that deal with electromagnetic waves. Peak-to peak displacement
is proportional to the Root Mean Square of the wave and the RMS is
proportional to the square root of the power. So if there is 4 times less
power in the gravitational wave (because the source is twice as far away)
the peak to peak displacement is only reduced by a factor of 2.

> So gravitational waves have intensities that drops with the square of the
> distance

I'm not disputing that, but that fact is not inconsistent with the fact
that LIGO's ability to detect gravitational wave sources only decreases
linearly with distance because with LIGO the key thing is peak to peak
displacement of the wave not its intensity.

John K Clark

>

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```

### Re: LIGO

```On Saturday, March 30, 2019 at 8:32:53 AM UTC-6, John Clark wrote:
>
> On Fri, Mar 29, 2019 at 8:05 PM Lawrence Crowell  > wrote:\
>
>
>> > Weak gravitational waves are very similar to electromagnetic waves,
>>
>
> From a practical point of view there are 2 differences:
>
> 1) Our ability to detect electromagnetic waves decreases with the square
> of the distance, but LIGO's ability to detect gravitational waves only
> decreases linearly with distance because unlike film or CCD cameras LIGO
> does not detect the energy in the wave it detects the displacement the wave
> produces.
>

An antenna or any receiver of electromagnetic waves in effect measures the
displacement of electrons or equivalently a current is produced. This is
associated by Maxwell's equation by electric and magnetic fields with
energy. A gravitational wave is measured according to strain, but a strain
through distance has an energy content as well.

Let us think about very weak gravitational waves. The metric for weak
gravitational fields is a flat space metric plus a perturbing particular

g_{ab} = η_{ab} - h_{ab}.

This perturbing metric has 10 independent elements. We now eliminate the
diagonal elements from the metric h_{ab} with a trace condition, which
leaves only 6 independent variables.

The Christoffel symbols are

Γ^a_{bc} = ½g^{ad}(∂_cg_{db} + ∂_bg_{dc} - ∂_dg_{bc}),

Where linear in the perturbing term this is

Γ^a_{bc} = ½(∂_ch^a_b + ∂_bh^d_c - ∂^ah_{bc}).

Now we compute the Riemann curvature tensor and eliminate the Γ^2 terms as
O(h^2) and so we have

R^a_{bcd} = ∂_cΓ^a_{bd} - ∂_dΓ^a_{bc}

∂_b∂_ch^a_d - ∂^a∂_ch_{bd} + ∂^a∂_dh_{bc} - ∂_b∂_dh^a_c.

The first line above should look familiar for anyone who knows
electromagnetic theory as a commutator of coordinates on a differential and
gauge connection.

The Einstein field equation may be written as R_{ab} - ½Rg_{ab} =
8πGT_{ab}, as well as the form R_{ab} = 8πG(T_{ab}  - ½ Tg_{ab}) where the
Ricci curvature and Ricci curvature scalar are computed with a lot of
contraction on indices to get

□h_{ab} + ∂_a∂_bh - ∂_a∂_ch^c_b - ∂_a∂_ch^c_b = 8πG(2T_{ab} - ½ Tg_{ab}).

That is a complicated looking differential equation, but it is
underdetermined. This equation has 6 variables and we need to eliminate 4
of them. Now this requires a gauge-like condition as with electromagnetism.
The standard one is Γ^a_{bc}g^{bc} = 0. which in our linearized gravity
contains first order derivatives of h_{ab}. This looks similar to the
Coulomb or Lorentz gauge in electromagnetism. This gauge condition is then
∂^bh_{ab} = ½∂_ah and this eliminates lots of stuff as we get

□h_{ab} = 8πG(2T_{ab} - ½ Tg_{ab}).

This looks a lot more like a wave equation, where for T_{ab} = 0 in source
free region this is □h_{ab} = 0, and the box is the d'Alembertian second
order with

∂^i∂_ih_{ab} - ∂^2_th_{ab} = 0

which is a familiar wave equation. This wave equation has not just one term
but two, which correspond to the two helicity states of a gravitational
wave. For a spherically symmetric wave the intensity will drop as 1/r^2
from the point of origin. Waves at higher orders may have quadrupole and
dipole terms and even higher, but for sufficient distance from the source
it becomes more spherically symmetry FAPP. So gravitational waves have
intensities that drops with the square of the distance far removed from the
source.

This is the first order wave equation most used to compute expected
gravitational waves at the LIGO. The complicated stuff is in using the
2T_{ab} - ½ Tg_{ab} for the generation of gravitational waves by imploding
matter. The collision of black holes means one needs to expand the terms
with

g_{ab} = η_{ab} - h^1_{ab} - h^2_{ab} - h^2_{ab}

where these higher orders in h deviate from the linearity with orders
below. This is similar to post-Newtonian formalism, but once you have
h^1_{ab} you use those to compute h^2_{ab} linear in h^2_{ab}, but with O((
h^1_{ab})^2) terms, and then continue to the next order and … . Then to get
Euler angles etc.

LC

>
> 2) It's easy for telescopes to determine the direction electromagnetic
> waves are coming from but difficult to determine its distance, with LIGO
> it's easy to determine the distance from the gravitational wave source but
> hard to determine the direction it's coming from.
>
>  > The graviton is quantum mechanically much the same as biphotons that
>> occurs with bunching or Hanbury Brown and Twiss physics.
>>
>
> LIGO can not detect gravitons and even if the graviton exists I am
> skeptical anyone will ever be able to detect it.
>
> > The main advantage of having a third LIGO is that now the source can be
>> triangulated more accurately.
>>
>
> It also increases sensitivity. If you get a small jump above the noise
> level in just 2 detectors that may not be enough to reach the 5 sigmas
> needed to claim a ```