LIGO Event Trigger Timing
LIGO was designed to detect a tiny ripple in Earth's crust caused by a gravitational wave from a distant inspiral merger.
The LIGO 'trigger timing' is interesting; this trigger determines when LIGO will declare a gravitational wave detection event.
There is a pattern for a trigger for LIGO detections.
The timing of tidal events is related to the Earth's rotation and the revolution of the moon around the Earth. If the moon was stationary in space, the tidal cycle would be 24 hours long. However, the moon is in motion revolving around the Earth. One revolution takes about 27 days and adds about 50 minutes to the tidal cycle. As a result, the tidal period is 24 hours and 50 minutes in length.
The second factor controlling tides on the Earth's surface is the Sun's gravity. The height of the average solar tide is about 50% the average lunar tide. At certain times during the moon's revolution around the Earth, the direction of its gravitational attraction is aligned with the Sun's. During these times the two tide producing bodies act together to create the highest and lowest tides of the year. These spring tides occur every 14-15 days during full and new moons.
The combination of the ocean tide and Earth's rotation results in essentially a slow wave moving across the ocean's surface over the course of a day.
Earth tide is the displacement of the solid earth's surface caused by the gravity of the Moon and Sun. Its main component has meter-level amplitude at periods of about 12 hours and longer.
A new moon or full moon cause a significant earth tide with the Sun also aligned. A perigee has an earth tide regardless of the Sun.
The Earth's crust is solid, unlike the fluid oceans. This disturbance is spread across many square miles but it cannot begin or end smoothly like a fluid.
However it is essentially a slow wave in the crust.
This wave is affecting LIGO which is looking for a gravitational wave affecting the crust.
The celestial events causing an earth tide in this time period: Full Moon, New Moon, PeriGee, PeriHelion, MJ = Moon-Jupiter alignment on 2019-04-23.
More than one LIGO event has been triggered and detected in the ripples from one earth tide event. This indicates the erratic disturbance can result in more than one trigger.
There are 41 LIGO events and 22 earth tide events in the following list.
This list has the LIGO events in chronological order but preceded by the associated earth tide event. LIGO events can be reported before or after the earth tide event whose effect is over a span of time.
The LIGO 'trigger mechanism' for when to declare an event is sensitive to the prolonged disturbance in the crust of an earth tide. Frequently there is only a one day mismatch.
The lines starting with GW or S are the LIGO events.
NM-15-09-13 --- caused one LIGO trigger after this day
GW150914 _ event 1 day after NM
NM-15-10-12 --- caused one trigger on this day
GW151012 _ same day as NM
FM-15-12-25 --- caused one trigger after this day
GW151226 _ 1 day after FM
PH-17-01-04 --- caused one trigger on this day
GW170104 _ same day as PH
PG-17-04-15 --- caused one trigger, before this event
S190412 _ 3 days before PG
FM -17-06-09 --- caused one trigger, before this event
GW170608 _ 1 day before FM
GW170608 _ 1 day before FM
NM-17-07-23 --- caused one trigger, after this event
GW170729 _ 6 days after NM
FM-17-08-07 --- caused one trigger, after this event
GW170809 _ 2 days after FM
PG-17-08-18 _ caused 3 events, 2 before and 1 on this day
GW170814 _ 4 days before PG
GW170817 _ 1 day before PG
GW170818 _ same day as PG
NM-17-08-21 _ solar eclipse --- caused one trigger, after this event
GW170823 _ 2 days after NM
NM-19-04-05 --- caused one trigger, after this event
S190408an _ 3 days after NM
PG-19-04-16 --- caused one trigger, before this event
S19040412m 4 days before PG
MJ-19-04-23_ resulted in 3 triggers, 1 before, 2 after
S190421 _ 2 days before MJ
S190425z _ 2 days after MJ
S190426c _ 3 days after MJ
NM-19-05-04 _ resulted in 2 triggers, 1 before, 1 after
S190503bf _ 1 day before NM
S190510g _ 6 days after NM
FM-19-05-18 _ resulted in 6 triggers, 3 before, 3 after
S190512at _ 6 days before FM
S190513bm _ 5 days before FM
S190517h _ 1 day before FM
S190519bj _ 1 day after FM
S190521g _ 3 days after FM
S190521r _ 3 days after FM
NM-19-06-03 _ caused one trigger, before this event
S190602aq _ 1 day before NM
NM-19-07-02 _ solar eclipse _ resulted in 4 triggers, 2 before, 2 after
S190630ag _ 2 days before NM
S190701br _ 1 day before NM
S190706ai _ 4 days after NM
S190707q _ 5 days after NM
FM-19-07-18_ caused one trigger, after this event
S190720a _ 2 days after FM
NM-19-07-31_ caused 2 triggers, both before this event
S190727h _ 4 days before NM
S190728q _ 3 days before NM
FM-19-08-15 _ one trigger before this event
S190814bv _ 1 day before FM
NM-19-08-30_ caused 3 triggers, 2 before, 1 after
S190828j _ 2 days before NM
S190828l _ 2 days before NM
S190901ap _ 2 days after NM
FM-19-09-13 -- caused 3 triggers, 2 before, 1 after
S190910d _ 3 days before FM
S190910h _ 3 days before FM
S190915ak _ 2 days after FM
NM-19-09-28 -- caused 2 triggers before
S190923y _ 5 days before NM
S190924h _ 4 days before NM
Whether the trigger was before after the event appears random. I imagine the response in the crust to an earth tide is not always consistent in the very long detectors.
Many of the LIGO events were just a day or two before or after the earth tide event.
All 41 LIGO events were within 6 days of an earth tide event.
In other words, LIGO had no events without an associated earth tide event.
LIGO had no events during spans which included earth tide events:
2016 no events in 2016
2017 February, March, May, September through December
2018 no events in 2018
2019 January through March
The above observations indicate LIGO can trigger on or near the start of an earth tide disturbance, also trigger near the end of the earth tide, and even trigger more than once during its duration.
The LIGO design has no method to filter out a ripple from an Earth tide. The design simply looks for a template in the data from the 'world's most sensitive GW project' and upon a verification (by a very high probability) of that template a detection is recorded.
In practice, an earth tide disturbance is coincident with one or more wave detections.
The earth tide is a much larger disturbance than that expected from a distant inspiral merger.
LIGO needs independent confirmation for credibility when it declares a gravitational wave detection. Right now each LIGO detection could be from either a merger or something else, like an earth tide. Only the one claimed NS-NS event had a gamma ray burst recorded that day though that one is suspicious. None of the others have anything.
Without a confirmation for each, we don't know how many are correct.
As a software programmer I know either all claims are verified or some results could be a lucky outcome from the software with a problem revealed later.
LIGO has no known merger event to verify their model for each template.
This observation indicates an earth tide triggers the LIGO analysis of its data looking for a template.
With that, either the analysis is 100% accurate or it could be declaring false detections.
Confirmations do not accompany all detections.
Even if one doubts only the LIGO analysis, many scientists doubt the possibility of a gravitational wave. Many scientists know gravity must be instantaneous. For example, the orbits of all bodies in our solar system cannot possibly remain stable with that time delay. Isaac Newton when he described gravity (the first to do so, with an equation) knew gravity must be instantaneous.
If gravity is instantaneous then there is no wave; LIGO cannot detect the invalid prediction of a mistake.
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Last updated (09/26/2019)
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