Starship Asterisk*

by **Chris Peterson** » Mon Dec 29, 2008 11:24 pm

neufer wrote:I'll bet that he was a good lecturer; but "the phone book" had a significant gravitational field of its own as I recall.

He's a very funny guy; the classes were most entertaining (not to mention enlightening). I've got the book sitting on the shelf right behind me, and that shelf is definitely sagging.

by **neufer** » Mon Dec 29, 2008 10:59 pm

Chris Peterson wrote:
neufer wrote:
I took a course under Misner using _Gravitation_ (Misner, Thorne, Wheeler 1973).
Cool. I had a class from Thorne, using the same text, of course.

I'll bet that he was a good lecturer;
but "the phone book" had a significant gravitational field of its own as I recall.

by **neufer** » Mon Dec 29, 2008 10:54 pm

apodman wrote:If we are to be historians and use "B.C.E." instead of "B.C.",
why don't we go all the way and use "C.E." instead of "A.D."?

People at the time actually used "A.D." but never "B.C."
"Historical reference only" (as bystander would say).

by **Chris Peterson** » Mon Dec 29, 2008 10:51 pm

neufer wrote:This isn't really an issue on whether an one person IS ALLOWED to choose their own space-time coordinates quite freely; this is an issue about THE FACT that modern human society (with the exception of Liberia, Myanmar and some Lockheed Martin engineering teams) has ALREADY CHOSEN a well defined space-time coordinate system. And as almost any astronomer will tell you, that CHOSEN system states quite clearly that when we look out at the universe through our telescopes we are ALSO looking back in time. To be precise: we see Deneb as it was 3,000 years ago (not as it was 2,000 years ago, nor 1,000 years ago, nor as it is today). If you have a problem with THAT FACT then go argue with the astronomers.

In no way does a widely accepted, defined spacetime coordinate system alter what I said. Neither did I say that looking outward isn't equivalent to looking back in time. I only pointed out that simultaneity is a tricky concept, and that by one well accepted frame of reference it is proper to say that an event happens at the same time it is observed (assuming the information travels at c). Time and space can be interchangeable concepts, both measured in the same units.

I took a course under Misner using _Gravitation_ (Misner, Thorne, Wheeler 1973).

Cool. I had a class from Thorne, using the same text, of course.

by **apodman** » Mon Dec 29, 2008 10:25 pm

If we are to be historians and use "B.C.E." instead of "B.C.", why don't we go all the way and use "C.E." instead of "A.D."?

by **neufer** » Mon Dec 29, 2008 10:08 pm

Chris Peterson wrote:
neufer wrote:
Chris Peterson wrote:Whoa...! This seems to be an excessively esoteric answer from Chris.

Our earth based time system is quite well defined and it makes perfect sense to say that SN1054 took place at a point in space time D light years away and D+954 years in the past. The real problem lies in the fact that D is a little hard to define precisely with current technology.
Not really esoteric at all; quite mainstream, actually.

Have you read Spacetime Physics by Taylor and Wheeler? This book on special relativity has one of the finest explanations of spacetime I've seen (and I had the good fortune to receive that particular physics lecture from Richard Feynman). Imagine the Universe built up from a 3D orthogonal latticework of meter sticks, with a clock at each junction. The question is, how do you synchronize the clocks? One standard method is to set your local clock to zero, then set off an omnidirectional flash of light. As an observer at each vertex sees the light, he resets his own clock. It is only when we imagine ourselves outside this Universe that we believe the clocks are all showing different times. That's because we define a sort of "super simultaneity". But from within the Universe, embedded as we are in spacetime, the clocks can be treated as being synchronized.

In the most basic, special relativity oriented viewpoint, it is perfectly reasonable to say that the supernova happened when we observed it. My making that statement has nothing to do with any practical difficulty in figuring out the value of D. Because our worldview is such that space and time are perceived as different things, we like to extract time from space, and therefore ask "when did it really happen?" But that question isn't easy to answer, not least because the question as stated has more than one correct answer.

I took a course under Misner using _Gravitation_ (Misner, Thorne, Wheeler 1973).

This isn't really an issue on whether an one person IS ALLOWED to choose their own space-time coordinates quite freely; this is an issue about THE FACT that modern human society (with the exception of Liberia, Myanmar and some Lockheed Martin engineering teams) has ALREADY CHOSEN a well defined space-time coordinate system. And as almost any astronomer will tell you, that CHOSEN system states quite clearly that when we look out at the universe through our telescopes we are ALSO looking back in time. To be precise: we see Deneb as it was 3,000 years ago (not as it was 2,000 years ago, nor 1,000 years ago, nor as it is today). If you have a problem with THAT FACT then go argue with the astronomers.

When SN 1054 exploded, the Chinese, Japanese, Arabs & Anasazi probably all agreed that it was happening right then & there but we no longer concur with that assumption. And, perhaps, there is some Galactic Federation out there who once all agreed to synchronize their clocks by the burst of neutrinos that came out of SN 1054 ... but we have yet to join that Federation.

by **Chris Peterson** » Mon Dec 29, 2008 7:07 pm

neufer wrote:
Chris Peterson wrote:Whoa...! This seems to be an excessively esoteric answer from Chris.

Our earth based time system is quite well defined and it makes perfect sense to say that SN1054 took place at a point in space time D light years away and D+954 years in the past. The real problem lies in the fact that D is a little hard to define precisely with current technology.

Not really esoteric at all; quite mainstream, actually.

Have you read Spacetime Physics by Taylor and Wheeler? This book on special relativity has one of the finest explanations of spacetime I've seen (and I had the good fortune to receive that particular physics lecture from Richard Feynman). Imagine the Universe built up from a 3D orthogonal latticework of meter sticks, with a clock at each junction. The question is, how do you synchronize the clocks? One standard method is to set your local clock to zero, then set off an omnidirectional flash of light. As an observer at each vertex sees the light, he resets his own clock. It is only when we imagine ourselves outside this Universe that we believe the clocks are all showing different times. That's because we define a sort of "super simultaneity". But from within the Universe, embedded as we are in spacetime, the clocks can be treated as being synchronized.

In the most basic, special relativity oriented viewpoint, it is perfectly reasonable to say that the supernova happened when we observed it. My making that statement has nothing to do with any practical difficulty in figuring out the value of D. Because our worldview is such that space and time are perceived as different things, we like to extract time from space, and therefore ask "when did it really happen?" But that question isn't easy to answer, not least because the question as stated has more than one correct answer.

by **neufer** » Mon Dec 29, 2008 6:03 pm

Chris Peterson wrote:
ahen wrote:Thanks for the response. Let me see if I've got it.

It is unknown when the explosion actually happened, but given an estimated distance of 6,000 light years probably around 5,000 BC. We observed it first 1,000 years ago (roughly). So the first supernova "blast" photons from a 6,000 year old event reached Earth in 1054. We are 1,000 years from the encounter with the photons, not the crab pulsar. The supernova event happened 7,000 years ago.
That's generally correct- or at least, one way of looking at it. However, dating any event that is far away is an iffy business, and to many theorists unnecessary. The whole idea of "simultaneity" needs to be carefully defined within relativity theory. It is, in fact, a perfectly reasonable and consistent viewpoint to say that the supernova actually happened 1000 years ago, not just that its light reached us then. This is the natural result of the way that space and time are inextricably entwined. Which way you choose to look at it really depends on the question you're trying to answer, not on what is "real".

Whoa...! This seems to be an excessively esoteric answer from Chris.

Our earth based time system is quite well defined and it makes perfect sense to say that SN1054 took place at a point in space time D light years away and D+954 years in the past. The real problem lies in the fact that D is a little hard to define precisely with current technology.

Likewise, the boundaries of many western U.S. states were defined according to the American Meridian NOT the Greenwich Meridian primarily because land surveying was the only accurate technology at the time:
http://en.wikipedia.org/wiki/Washington_meridian

by **neufer** » Mon Dec 29, 2008 5:46 pm

ahen wrote:Thanks for the response. Let me see if I've got it.

It is unknown when the explosion actually happened, but given an estimated distance of 6,000 light years probably around 5,000 BC. We observed it first 1,000 years ago (roughly). So the first supernova "blast" photons from a 6,000 year old event reached Earth in 1054. We are 1,000 years from the encounter with the photons, not the crab pulsar. The supernova event happened 7,000 years ago.

That's about right
--------------------------------------------
http://en.wikipedia.org/wiki/SN_1054
http://en.wikipedia.org/wiki/Crab_Pulsar
...............................
. ~5250 B.C.E.
.
A progenitor star located in the Milky Way galaxy at a distance of ~6,300 light years explodes as a core-collapse supernova.
...............................
. 1054 A.D.
.
The supernova is recorded by Chinese, Japanese, and Arab astronomers as being bright enough to see in daylight for 23 days and was visible in the night sky for 653 days. An Anasazi cliff painting near the great house of Penasco Blanco may portray it.

...............................
. 1774 A.D.
.
The cloudy remnants of SN 1054 are cataloged as Messier 1 or M1.
...............................
. 1930 A.D.
.
The notion of gaseous filaments and a continuum background was photographically confirmed by Walter Baade and Rudolph Minkowski in 1930: The filaments are apparently the remnants from the former outer layers of the former star (the "pre-supernova" or supernova "progenitor")
...............................
. 1953 A.D.
.
Soviet astronomer J. Shklovsky proposes that the inner, blueish nebula is highly polarised synchrotron radiation emitted by high-energy (fast moving) electrons in a strong magnetic field.
...............................
. 1956 A.D.
.
Shklovsky theory supported by polarised light observations of Jan H. Oort and T. Walraven (1956).

...............................
. April 1963 A.D.
.
M1 X-rays are detected with a high-altitude rocket of type Aerobee with an X-ray detector developed at the Naval Research Laboratory; the X-ray source was named Taurus X-1, and the energy emitted in X-rays by the Crab nebula is about 100 times more than that emitted in the visual light.
...............................
. September 1942
.
Two stars are observed near the center of the M1 (referred to in the literature as the "north following" and "south preceding" stars). In September 1942, Walter Baade rules out the north following star but finds the evidence inconclusive for the south preceding.Rudolf Minkowski, in the same issue of Astrophysical Journal as Baade, advances spectral arguments claiming the "evidence admits, but does not prove, the conclusion that the south preceding star is the central star of the nebula".
...............................
. late 1968,
.
David H. Staelin & Edward C. Reifenstein III reported the discovery of two pulsating radio sources "near the crab nebula that could be coincident with it" using the 300-foot Green Bank radio antenna. They were given the designations NP 0527 and NP 0532. A subsequent study by them including William D. Brundate found that the NP 0532 source is located at the Crab Nebula.
...............................
. February 1969
.
Optical pulsations 30 times each second reported by Nather, Warner, and Macfarlane.
----------------------------------------------------------------------------------------
----------------------------------------------------------------------------------------
http://en.wikipedia.org/wiki/Tsunami_2004
http://en.wikipedia.org/wiki/Timeline_o ... earthquake
...............................................
. Sunday, 26th December, 2004
...............................
. 00:58:53 UTC
.
The Great Sumatra-Andaman earthquake, with an epicentre off the west coast of Sumatra, Indonesia. With a magnitude of between 9.1 and 9.3, it is the second largest earthquake ever recorded on a seismograph. This earthquake had the longest duration of faulting ever observed, between 8.3 and 10 minutes. It caused the entire planet to vibrate as much as 1 cm (0.5 inches).
...............................
. 01:23 UTC
.
A tsunami hits the coast of Indonesia. Banda Aceh, a town in northwest Indonesia, receives seismic sea waves that are 9 meters in height. Effects of the tsunami reach 4 kilometers inland from the coastline. Just minutes prior to the tsunami, southeast Indonesia had sustained damage from the earthquake.
...............................
. 02:33 UTC
.
A tsunami hit the coastal villages in Sri Lanka.
...............................
. 02:33 UTC
.
A tsunami hits the coasts in Thailand. According to many witnesses, the first seismic sea wave hit the coast in Phuket at 02:33 UTC. Khao Lak was hit a few minutes later. A few tourists managed to receive warning calls of big waves from other tourists in Phuket. According to a lot of witnesses the tsunamis, 5-10 meters in height, came in 10 minute periods.
...............................
. 05:25 UTC
.
The first reading from the Australian National Tidal Centre gauge at Cocos Island west of Australia gave a reading of 0.5m crest-to-trough.
--------------------------------------------

by **Chris Peterson** » Mon Dec 29, 2008 5:25 pm

ahen wrote:Thanks for the response. Let me see if I've got it.

It is unknown when the explosion actually happened, but given an estimated distance of 6,000 light years probably around 5,000 BC. We observed it first 1,000 years ago (roughly). So the first supernova "blast" photons from a 6,000 year old event reached Earth in 1054. We are 1,000 years from the encounter with the photons, not the crab pulsar. The supernova event happened 7,000 years ago.

That's generally correct- or at least, one way of looking at it. However, dating any event that is far away is an iffy business, and to many theorists unnecessary. The whole idea of "simultaneity" needs to be carefully defined within relativity theory. It is, in fact, a perfectly reasonable and consistent viewpoint to say that the supernova actually happened 1000 years ago, not just that its light reached us then. This is the natural result of the way that space and time are inextricably entwined. Which way you choose to look at it really depends on the question you're trying to answer, not on what is "real".

by **ahen** » Mon Dec 29, 2008 4:46 pm

Thanks for the response. Let me see if I've got it.

It is unknown when the explosion actually happened, but given an estimated distance of 6,000 light years probably around 5,000 BC. We observed it first 1,000 years ago (roughly). So the first supernova "blast" photons from a 6,000 year old event reached Earth in 1054. We are 1,000 years from the encounter with the photons, not the crab pulsar. The supernova event happened 7,000 years ago.

by **neufer** » Sun Dec 28, 2008 9:15 pm

ahen wrote:This APOD raised a question that's been on my mind, if the supernova is known to have occurred in 1054, why is its estimated distance 6,000 light years away? Don't we KNOW that it is 955 light years away? (I rolled the year 1 tick forward since its just a couple days away)

The supernova is known to have been observed on earth in 1054 A.D.

The supernova explosion actually took place some 6,000 years
before 1054 A.D. or ~ 5,000 B.C.E.

A tidal wave of photons from the supernova has now extended about 955 light years beyond earth.
We don't we KNOW if there are other observers 955 light years away who are just experiencing the supernova?

by **Chris Peterson** » Sun Dec 28, 2008 9:11 pm

ahen wrote:This APOD raised a question that's been on my mind, if the supernova is known to have occurred in 1054, why is its estimated distance 6,000 light years away? Don't we KNOW that it is 955 light years away? (I rolled the year 1 tick forward since its just a couple days away)

Because the convention is to ignore the light time. Unless there is some specific wording to the contrary, we refer to something happening when we observe it. And we observed it in 1054, regardless of when it "really" happened (which is a slippery question), or how far away it is.

by **ahen** » Sun Dec 28, 2008 8:01 pm

This APOD raised a question that's been on my mind, if the supernova is known to have occurred in 1054, why is its estimated distance 6,000 light years away? Don't we KNOW that it is 955 light years away? (I rolled the year 1 tick forward since its just a couple days away)

by **ta152h0** » Sun Dec 28, 2008 4:56 pm

You guys, astronomers and physicists are just awesome. Inventing all these toys that make these observations possible. awesome

by **neufer** » Sun Dec 28, 2008 2:49 am

bystander wrote:
neufer wrote:Gravitational & electromagnetic interactions do not violate parity.
Not sure what you mean by parity in this context, but electromagnetic fields affect electrons.
Would they not have an opposing affect on positrons?

The ceiling mirror image experiment of
two electrons impinging upon a clockwise spinning neutron star and jetting out the south pole is
two electrons impinging upon a clockwise spinning neutron star and jetting out the north pole.

The side mirror image experiment (analogous to the picture below) of
two electrons impinging upon a clockwise spinning neutron star and jetting out the south pole is
two electrons impinging upon a counterclockwise spinning neutron star and jetting out the south pole.

In either case the physics has changed in the mirror image situation
which can ONLY happen with parity violating WEAK INTERACTIONS:
-------------------------------------------------------------------

-------------------------------------------------------------------
The only parity consistent outcome for gravitational & electromagnetic interactions is for the two electrons impinging upon
a clockwise spinning neutron star to split with one jetting out the north pole and the other jetting out the south pole.

(Ditto for positrons.)

by **Chris Peterson** » Sun Dec 28, 2008 12:06 am

bystander wrote:Not sure what you mean by parity in this context, but electromagnetic fields affect electrons. Would they not have an opposing affect on positrons?

They do indeed. But antimatter is no more limited to positrons than ordinary matter is to electrons. So a mechanism that separates by charge will still send antiprotons and electrons in the same direction (or positrons and protons), so it won't prevent matter-antimatter annihilation from happening.

In any case, there's no evidence of significant charge separation occurring anywhere in the Universe. The electromagnetic force is simply too strong; there is no mechanism to keep the charges separated outside a very local area. That's why there are no electric currents flowing through the Universe.

by **bystander** » Sat Dec 27, 2008 9:59 pm

neufer wrote:Gravitational & electromagnetic interactions do not violate parity.

Not sure what you mean by parity in this context, but electromagnetic fields affect electrons. Would they not have an opposing affect on positrons?

by **neufer** » Sat Dec 27, 2008 9:44 pm

bystander wrote:Could it be that the jets of matter and anti-matter are directed to opposite poles by the intense electromagnetic field?

No.

Gravitational & electromagnetic interactions do not violate parity.

by **Chris Peterson** » Sat Dec 27, 2008 8:51 pm

bystander wrote:I guess I expected more evidence of matter/anti-matter annihilation.

The usual result of matter-antimatter annihilation is photons with gamma radiation wavelengths. Seems to be plenty of that coming from M1. Is there some reason to assume we aren't seeing annihilation products in that? (I'd still expect the energy from such annihilation to be small compared with the synchrotron output, however).

by **bystander** » Sat Dec 27, 2008 8:32 pm

Chris Peterson wrote:There isn't much matter, and even less antimatter. The pulsar is producing synchrotron radiation- that's the energy source that's driving the emission nebula. I'm sure there are some collisions generating new particles, including antimatter, but on the whole the nebula would be considered a pretty good vacuum. Most of the effects are simply thermal, and the result is ions, not new particles.

I'm not sure what you would describe as spectacular: the Crab is already radiating over the entire EM spectrum, and is an optically bright object as well.

I agree the Crab Nebula is quite spectacular, as seen in these previous APODs:

APOD: 2006 October 26 - Composite Crab
APOD: 2005 December 2 - Crab Nebula Mosaic from HST
and others.

But both the HEAPOW and Chandra explanations indicated jets of matter and anti-matter streaming from the pulsar.

This image gives the first clear view of the faint boundary of the Crab Nebula's X-ray-emitting pulsar wind nebula. The nebula is powered by a rapidly rotating, highly magnetized neutron star, or pulsar (white dot near the center). The combination of rapid rotating and strong magnetic field generates an intense electromagnetic field that creates jets of matter and anti-matter moving away from the north and south poles of the pulsar, and an intense wind flowing out in the equatorial direction.

I guess I expected more evidence of matter/anti-matter annihilation. Could it be that the jets of matter and anti-matter are directed to opposite poles by the intense electromagnetic field?

HEAPOW: Blue Crab (2008 Nov 16)

by **Chris Peterson** » Sat Dec 27, 2008 7:49 pm

bystander wrote:The spinning pulsar and jets of matter and anti-matter aren't as obvious in the normal visible light photos of the Crab. But I was wondering, with so much matter and anti-matter spewing from the pulsar, why aren't there more spectacular displays from the Crab?

There isn't much matter, and even less antimatter. The pulsar is producing synchrotron radiation- that's the energy source that's driving the emission nebula. I'm sure there are some collisions generating new particles, including antimatter, but on the whole the nebula would be considered a pretty good vacuum. Most of the effects are simply thermal, and the result is ions, not new particles.

I'm not sure what you would describe as spectacular: the Crab is already radiating over the entire EM spectrum, and is an optically bright object as well.

by **neufer** » Sat Dec 27, 2008 3:40 pm

bystander wrote:http://apod.nasa.gov/apod/ap081227.html
http://heasarc.gsfc.nasa.gov/docs/objec ... andra.html

The spinning pulsar and jets of matter and anti-matter aren't as obvious in the normal visible light photos of the Crab. But I was wondering, with so much matter and anti-matter spewing from the pulsar, why aren't there more spectacular displays from the Crab?

http://chandra.harvard.edu/photo/2008/crab/
http://chandra.harvard.edu/photo/2006/crab/

High energy collisions will always generate jets of matter and anti-matter

but eventually the vacuum of space keeps further collisions to a minimum
with non-collisional synchrotron radiation dominating much of the EM spectrum:

by **bystander** » Sat Dec 27, 2008 6:30 am

http://apod.nasa.gov/apod/ap081227.html
http://heasarc.gsfc.nasa.gov/docs/objec ... andra.html

People from the Chesapeake Bay Area should appreciate this, an x-ray photo from Chandra of the pulsar at the heart of the Crab Nebula. The spinning pulsar and jets of matter and anti-matter aren't as obvious in the normal visible light photos of the Crab. But I was wondering, with so much matter and anti-matter spewing from the pulsar, why aren't there more spectacular displays from the Crab?

http://chandra.harvard.edu/photo/2008/crab/
http://chandra.harvard.edu/photo/2006/crab/

Starship Asterisk*

Blue Crab (2008 Dec 27)

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