Cosmology Views

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.

Ocean tides:
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:

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 50 LIGO events and 29 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 1 LIGO trigger after this day
GW150914 _ event 1 day after NM

NM-15-10-12 --- caused 1 trigger on this day
GW151012 _  same day as NM

FM-15-12-25 --- caused 1 trigger after this day
GW151226 _ 1 day after FM

PH-17-01-04 --- caused 1 trigger on this day
GW170104 _ same day as PH

PG-17-04-15 --- caused 1 trigger, before this event
S190412 _ 3 days before PG

FM -17-06-09 --- caused 1 trigger, before this event
GW170608 _ 1 day before FM

NM-17-07-23 --- caused 1 trigger, after this event
GW170729 _ 6 days after NM

FM-17-08-07 --- caused 1 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 1 trigger, after this event
GW170823 _ 2 days after NM

NM-19-04-05 --- caused 1 trigger, after this event
* S190408an _  3 days after NM 

PG-19-04-15 --- caused 1 trigger, before this event
S19040412m-   4 days before PG

FM-19-04-19_ resulted in 1 trigger after
S190421 _ 2 days after FM
MJ-19-04-23_ resulted in 2 triggers after
* 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

PG-19-05-13 _ resulted in 3 triggers, before
S190510g   3 days before PG
S190512at _ 1 day before PG
S190513bm _ same day as PG

FM-19-05-18 _ resulted in 4 triggers, 1 before, 3 after
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 1 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 1 trigger, after this event
S190720a _  2 days after FM

NM-19-07-31 -- caused 2 triggers, both before
S190727a _ 4 days before NM
S190728q  _ 3 days before NM

FM-19-08-15  -- caused 1 trigger before
S190814bv _ 1 day before FM

NM-19-08-30 --- caused 3 triggers, 2 before, 1 after
S190910d _  3 days before FM
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 4 triggers, 2 before, 2 after
S190923y _ 5 days before NM
S190924h _ 4 days before NM
S190930s _ 2 days after NM
S190930t _ 2 days after NM

FM-19-11-12 -- caused 2 triggers before
S191105e _ 7 days before FM
S191109d _ 3 days before FM

NM-19-11-26 -- caused 1 trigger
S191129u _ 3 days after NM

FM-19-12-12 -- caused 4 triggers 2 before, 2 after
S191204t_ 8 days before FM
S191205ah_ 7 days before FM
S191213g _ 1 day after FM

S191215w _ 3 days after FM

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 50 LIGO events were within 8 days of an earth tide event. 29 were within 2 days.

In other words, LIGO had no events without an associated earth tide event.

LIGO had no events during spans which included earth tide events:
2015 November ; O1 observing run began 2015 and ended 2017
2016 no events in 2016
2017 no events in February, March, May, September through December
2018 no events in 2018
2019 no events in January through March;  O3 observing run began April 1,2019
2019 no events in October LIGO off for maintenance

The above observations indicate LIGO will 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 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 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. not limited to the speed of light. For example, the orbits of all bodies in our solar system cannot possibly remain stable with that time delay caused by slow gravity. 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.

from LIGO
At its most sensitive state, LIGO will be able to detect a change in distance between its mirrors 1/10,000th the width of a proton!

LIGO is one of the most sophisticated scientific instruments ever built.  LIGO's detections will provide physicists with the means to answer key scientific questions, such as:

What are the properties of gravitational waves?
Is general relativity the correct theory of gravity?

(excerpt end)

In practice:

LIGO's detections will provide physicists with the means to answer key scientific questions, such as:
Did an earth tide event occur or is one beginning?

LIGO is so sensitive there are earth tide detections a few days before the peak of the wave from the earth tide in Earth's crust and additional detections are reported as the crust wave subsides because the Earth keeps rotating.
For example, the Full Moon peaked on 2019-05-18 but resulted in 6 detections, with 3 before the peak and 3 after the peak.

Nobel Prize:
the 2017 Nobel Prize in Physics was awarded to the pioneering leaders of the Laser Interferometer Gravitational-wave Observatory, or LIGO, for the first detection of gravitational waves.

(excerpt end)

LIGO was awarded the 2017 Nobel prize in physics for the first detection of an earth tide's wave event in Earth's crust using their extremely sensitive system.

Last updated (12/22/2019)