"We have detected gravitational waves. We did it."

[essentialsaltes]

Scientists announce discovery of clear gravitational wave signal, ripples in spacetime first predicted by Albert Einstein

 

[Michael]

Assuming this study is confirmed, congrats to the LIGO team. Nice.

I do have a couple of comments on the article itself:

Which is why on Thursday scientists around the world were able to hail the announcement as yet another confirmation of their “standard model” of the cosmos, and the beginning of a new era of discovery.

All this technically confirms is one aspect of GR theory itself. It's not a confirmation of "dark energy", or "dark matter", or "inflation", or anything else related to a full "cosmology theory". About the only thing it does confirm is the value of GR theory (again).

The most weird and wonderful prediction of Einstein’s theory was that everything came out of a single event: the Big Bang singularity. And we will be able to see what happened.”

GR theory doesn't "predict" that everything came from a single event. Only Lambda-CDM predicts such a thing. Einstein even embraced and discussed and entertained a static universe theory using GR, so this statement is simply false and misleading, just like so many other statements that are made by the mainstream.

Lambda-CDM proponents are constantly misleading the public with respect to the difference between GR theory and Lambda-CDM. GR theory doesn't require Lambda-CDM to be correct for it's scientific legitimacy. The reverse is not true.

 

[Look Up]

Cool. So has the speed of the gravitational wave also been measured or estimated ( esp. to be the speed of light)? Or are we witnessing a difference between waves that does not suggest speed (I don't know what that might mean)?

 

[Oafman]

Great write up from the Guardian, linked in the OP. Very layman friendly.

 

[Look Up]

"at the speed of light" http://www.livescience.com/53684-gravitational-waves-found.html

 

[essentialsaltes]

"at the speed of light"

At this point that is probably more of an assumption (based on the underlying theory) than a direct measurement of the speed by this detection.

 

[Michael]

At this point that is probably more of an assumption (based on the underlying theory) than a direct measurement of the speed by this detection.

I suspect that you are correct. I would think that you'd need to be able to triangulate the signal and know the exact origin/direction of the event to a high degree of accuracy in order to verify the propagation speed.

 

[Murby]

Current telescopes can only see back in time to about a million years after the big bang. Gravitational waves will allow observations to within a billionth of a second...

Comparing gravitational waves to our current observation technologies is like comparing television to radio. A whole new era of astronomy is about to open wide up.. The rate of new discoveries and understanding is about to greatly accelerate.

 

[Loudmouth]

At this point that is probably more of an assumption (based on the underlying theory) than a direct measurement of the speed by this detection.

If the gravitational waves reached the detectors the same time that the collision was seen in the telescope, then it would indicate that light and gravitational waves travel at the same speed.

 

[Michael]

If the gravitational waves reached the detectors the same time that the collision was seen in the telescope, then it would indicate that light and gravitational waves travel at the same speed.

In theory if we see the same signal in several detectors, it should arrive at each detector at slightly different times depending on the location of each detector.

 

[Wgw]

Good. That said, correct me if I am wrong, we are still far from detecting the hypothetical graviton particle?

 

[Loudmouth]

In theory if we see the same signal in several detectors, it should arrive at each detector at slightly different times depending on the location of each detector.

In theory, if gravitational waves are travelling at the speed of light, then they should arrive at the same time as the light produced by the merger of the black holes. If gravitational waves were faster or slower than light, then they would arrive before or after the observation of the merger.

 

[Murby]

In theory, if gravitational waves are travelling at the speed of light, then they should arrive at the same time as the light produced by the merger of the black holes. If gravitational waves were faster or slower than light, then they would arrive before or after the observation of the merger.

Your assumption assumes that they both originate from the same starting point. They discovered this issue with neutrino's and found that the travel time to our detectors was different because the light the event created came from a different point within the event than where the neutrinos were created.

 

[Loudmouth]

Your assumption assumes that they both originate from the same starting point.

The evidence is strongly in favor of it.

"Not only had the detector picked up the collision of two enormous black holes across a distance of almost 1bn light years of space, it recorded the distinctive “chirp” as the two spiralled towards each other."
https://www.theguardian.com/science...scovery-hailed-as-breakthrough-of-the-century

The changes in gravitational waves matched the spiraling orbits of the black holes.

They discovered this issue with neutrino's and found that the travel time to our detectors was different because the light the event created came from a different point within the event than where the neutrinos were created.

Over a 1 billion light year distance, any differences would have to be really small.

 

[Michael]

Good. That said, correct me if I am wrong, we are still far from detecting the hypothetical graviton particle?

Correct. The existence of gravity waves are a prediction of GR theory rather than a QM oriented prediction of gravity, so their discovery really doesn't help QM oriented concepts of gravity.

 

[Michael]

In theory, if gravitational waves are travelling at the speed of light, then they should arrive at the same time as the light produced by the merger of the black holes. If gravitational waves were faster or slower than light, then they would arrive before or after the observation of the merger.

I would agree with that logic as well.

Theoretically gravity waves would always travel at C even if light itself interacts with the medium of spacetime. In theory at least, the gravity wave signal could arrive *ahead* of light from the same event assuming that photons interact with the medium.

 

[Look Up]

At this point that is probably more of an assumption (based on the underlying theory) than a direct measurement of the speed by this detection.

After posting, I suspected the same.

 

[essentialsaltes]

If the gravitational waves reached the detectors the same time that the collision was seen in the telescope, then it would indicate that light and gravitational waves travel at the same speed.

This is true, but as far as I know, the collision was not seen by anything other than the gravitational wave detector.

 

[Loudmouth]

This is true, but as far as I know, the collision was not seen by anything other than the gravitational wave detector.

After further reading, you are correct. I saw mention of orbit periods and thought that came from visual data.

There was a delay between the detection at the two detectors. However, I think they are assuming the velocity of the gravitational waves in order to find the location of the event. If the event occurred at a point in the sky equidistant between the two detectors then the event would be detected at the same time.

 

[Michael]

After further reading, you are correct. I saw mention of orbit periods and thought that came from visual data.

There was a delay between the detection at the two detectors.

There should be. One should be slightly closer to the event than the other, and the signals should therefore arrive at slightly different times. I think you'd need at least three detectors to triangulate the location of the event to any serious degree of accuracy, and then you could more accurately calculate the propagation speed of the event.

However, I think they are assuming the velocity of the gravitational waves in order to find the location of the event.

Sounds about right.

If the event occurred at a point in the sky equidistant between the two detectors then the event would be detected at the same time.

Agreed.

The interesting aspect of finally detecting gravity waves is that may give us a way to verify or falsify the premise that light from distant events always travels at C.

Unless I'm mistaken, gravity should always propagate at C. Light from distant objects could however interact with the medium between the event and the Earth, and therefore light from any given event may not reach us as soon as the gravitational wave.