I like how they state clearly that the result they obtained, even though unexpected, does mean that there are things that we still do not know, not that all we know must be burned to the ground.
I also like how their possible suggestions for why theories might not be panning out points to not enough understanding about something. So now we have a new scientific understanding to pursue. And on the way to figuring out /that/ new thing, we'll probably run into even more questions that need answering!
In some ways, this is exciting - deepening mysteries always provoking further study. But on the flip side, it also makes me ponder the thought that maybe we will never gain true knowledge of the universe. At least, probably not before a very long time passes.
> But on the flip side, it also makes me ponder the thought that maybe we will never gain true knowledge of the universe.
Therefore, we might need to address the problem from the other end. This requires a totally different mindset. See for example the work done here: [1], or see the video lectures starting here: [2]
It's been 472 since humanity realized the Earth moves around a star, 328 years since we knew the equations of gravitation, only 100 since we learned about GR, and only 15 years since we were certain the universe is expanding.
I think we might be excused to take a few more years to nail down the rest of gravitation. There's an embarrassment of riches of data; it just needs assembling into a picture.
maybe we will never gain true knowledge of the universe
If you are equating true knowledge with perfect knowledge, this obviously should be considered a straw-man. There is no reason why the rules completely describing universe should have to fit in a human mind. Our brains were evolved to solve the specific context of our prehistoric survival.
It goes deeper than that. I think the human mind is fundamentally incapable of understanding Nature and reality. We make clever models, increasingly sophisticated and successful at manipulating matter and energy within the limited realm of our perception.
However, we will never truly grasp the outside World. Every discovery will open up another can of worms, in an endless chase for more refined models. Today it's Dark Energy and Dark Matter. Centuries from now our views will seem as naïve and simplistic as Phlogistics and 19th-century Ether.
That's OK though, as long as we're having fun. And don't blow ourselves up. And love and laugh.
I’ve always felt that theoretical physicists should give more thought to the implication that gravitational waves don’t exist. Just maybe it would require reworking relativity in a way that’s more compatible with quantum mechanics. Sadly, it seems that everyone seems to think the flaw is with the standard model not the other way around.
A lack of gravitational waves would mean information can travel infinitely fast, a Lorentz violation. There's no evidence in QM (or anywhere, really) that this is true.
Ok, assume gravitational influence travels at the speed of light.
Now imagine you pick up a heavy object (the Earth, say) and wave it back and forth. Can you see how the spreading gravitational influence manifests itself as a wave?
I'd rather take evidence from observation than from QM: let theory burn, as the current paradigm surely will if science ever trumps politics and regains its senses.
I had thought that the lack of gravitational waves makes it harder to reconcile with QM. It would be as if you could not detect real photons, only observe the indirect effect of virtual photons.
The fact that gravitational waves must exist follows from the idea that information must travel at a finite speed. Whatever theory you come up with, if it has a causal structure, it will have a wave structure.
You'd think a binary pulsar would be ideal for measuring gravitational waves: they're precise clocks swimming in rapidly changing gravitational fields.
Interestingly, binary systems of pulsars are the only source of evidence for gravitational waves. Astronomers use the pulsar timing to detect the slowing of orbital motion due to gravitational wave emission. I wonder if it's possible to detect a 'local gravitational wave background' modulating the pulsar timing on top of the usual modulation from the slowing binary.
> Astronomers use the pulsar timing to detect the slowing of orbital motion due to gravitational wave emission.
Correct, at least that's the theory
But that's not evidence of gravitational waves per se, rather an evidence that a spinning binary system will have a velocity decay (and gravitational waves fit the description of what might be happening)
So maybe there's an issue with how we measure it, how it actually affects matter or "it's complicated"/"it doesn't exist"
But the rate of orbital decay of pulsars in binary systems is very precisely matched by general relativity, which is going to be very hard to explain with a different cause.
Given that GR has been verified so thoroughly, while on the other hand models of the gravitational background depend on so many assumptions and simulations and approximately measured empirical relationships about supermassive black hole (SMBH) sizes, occurrences, time for SMBH mergers, etc, as detailed in the article, clearly this is incredibly weak evidence that gravitational waves don't exist. But something is wrong somewhere.
Good question. You don't need to directly observe every rotation in order to "account" for it. The drift rate for a pulsar is extremely low, so as long as you sync up often enough that the error is much smaller than one cycle you can be confident that you've counted every one even though you haven't directly measured them all.
Since they contain energy, they in turn have mass, and a gravitational field of their own.
Which is quite an interesting implication, because since they travel at the speed of light, they can't slow down when interacting with mass, instead they must do some sort of "blue shift".
It also means that when the waves are bent by traveling near a large mass, those waves emit daughter waves of their own.
And one part of the gravitational wave is attracted by another part of it.
I suspect that a combination of those processes adds so much noise that there is no detectable signal left.
> Since they contain energy, they in turn have mass,
That is not true...
> and a gravitational field of their own.
... although this is.
It's energy that creates a gravitational field, of which mass is a (usually dominant) subset. It does not mean anything with energy has mass. See: light.
Edit: also, the basic theory of gravitional waves is "linearized", which means that this kind of self-interaction is weak. That doesn't mean it doesn't happen, but it wouldn't resemble radiation if the effect is strong.
You misunderstand the difference between rest mass, invariant mass, and relativistic mass.
Invariant mass is the same in all reference frames, so light can possess it (if there are multiple photons, or they are in a box).
That is my preferred mass.
Rest mass excludes photons, but there is no reason to do so most of the time, since the mass of the photon acts exactly like mass in most things except when dealing with change in velocity.
Relativistic mass is special and depends on the relative motion between the objects.
In any case gravitational waves posses invariant mass, so essentially they do have mass, and if you could hold them you could weigh them on a scale.
> since the mass of the photon acts exactly like mass in most things except when dealing with change in velocity
Right: inertia. Funny that.
The fact that photons are affected by gravitational fields, even though they're massless, was a major victory for the theory of general relativity. It wouldn't be a big deal if you could just say the photon has mass. Because it doesn't.
A photon is massless. Fullstop. To say otherwise is to use a nonstandard definition of "mass". At best, people won't know what you're talking about. At worst, they will assume you don't. You should be more specific next time.
That will be huge if true. Gravity wave will tell us many things about the very early universe(first few 100,1000s of years!), for which we have very little data now. Its an amazing achievement for LIGO just after 10 days of its start.
I work in numerical relativity and our group produces many, many gravitational waveforms. I even visited LIGO this past summer. If Lawrence Krauss isn't bullshitting (and I have no reason to doubt he would be) then this is absolutely huge news. Nobel Prize worthy discovery no question.
41 comments
[ 3.9 ms ] story [ 96.3 ms ] threadIn some ways, this is exciting - deepening mysteries always provoking further study. But on the flip side, it also makes me ponder the thought that maybe we will never gain true knowledge of the universe. At least, probably not before a very long time passes.
Therefore, we might need to address the problem from the other end. This requires a totally different mindset. See for example the work done here: [1], or see the video lectures starting here: [2]
[1] http://www.liv.ac.uk/physical-sciences/events/fpl/
[2] https://www.youtube.com/watch?v=W2XdhzCORbo
I think we might be excused to take a few more years to nail down the rest of gravitation. There's an embarrassment of riches of data; it just needs assembling into a picture.
If you are equating true knowledge with perfect knowledge, this obviously should be considered a straw-man. There is no reason why the rules completely describing universe should have to fit in a human mind. Our brains were evolved to solve the specific context of our prehistoric survival.
However, we will never truly grasp the outside World. Every discovery will open up another can of worms, in an endless chase for more refined models. Today it's Dark Energy and Dark Matter. Centuries from now our views will seem as naïve and simplistic as Phlogistics and 19th-century Ether.
That's OK though, as long as we're having fun. And don't blow ourselves up. And love and laugh.
Now imagine you pick up a heavy object (the Earth, say) and wave it back and forth. Can you see how the spreading gravitational influence manifests itself as a wave?
Interestingly, binary systems of pulsars are the only source of evidence for gravitational waves. Astronomers use the pulsar timing to detect the slowing of orbital motion due to gravitational wave emission. I wonder if it's possible to detect a 'local gravitational wave background' modulating the pulsar timing on top of the usual modulation from the slowing binary.
Correct, at least that's the theory
But that's not evidence of gravitational waves per se, rather an evidence that a spinning binary system will have a velocity decay (and gravitational waves fit the description of what might be happening)
So maybe there's an issue with how we measure it, how it actually affects matter or "it's complicated"/"it doesn't exist"
Given that GR has been verified so thoroughly, while on the other hand models of the gravitational background depend on so many assumptions and simulations and approximately measured empirical relationships about supermassive black hole (SMBH) sizes, occurrences, time for SMBH mergers, etc, as detailed in the article, clearly this is incredibly weak evidence that gravitational waves don't exist. But something is wrong somewhere.
Isn't this pulsar just being watched by one radio telescope in Australia, which presumably can't point at it 24 hours a day?
Since they contain energy, they in turn have mass, and a gravitational field of their own.
Which is quite an interesting implication, because since they travel at the speed of light, they can't slow down when interacting with mass, instead they must do some sort of "blue shift".
It also means that when the waves are bent by traveling near a large mass, those waves emit daughter waves of their own.
And one part of the gravitational wave is attracted by another part of it.
I suspect that a combination of those processes adds so much noise that there is no detectable signal left.
That is not true...
> and a gravitational field of their own.
... although this is.
It's energy that creates a gravitational field, of which mass is a (usually dominant) subset. It does not mean anything with energy has mass. See: light.
Edit: also, the basic theory of gravitional waves is "linearized", which means that this kind of self-interaction is weak. That doesn't mean it doesn't happen, but it wouldn't resemble radiation if the effect is strong.
We are using different definitions of mass. I'm calling invariant energy mass, you are calling rest energy mass.
> but it wouldn't resemble radiation if the effect is strong
The wave does have a frequency though, which must blueshift as it interacts with matter.
Modern physics only refers to rest mass [1] as 'mass', otherwise people tend to get confused about how 'relativistic mass' (γm) affects gravity.
[1] E/c^2 in a centre of momentum frame, which doesn't exist for an object travelling at c
Invariant mass is the same in all reference frames, so light can possess it (if there are multiple photons, or they are in a box).
That is my preferred mass.
Rest mass excludes photons, but there is no reason to do so most of the time, since the mass of the photon acts exactly like mass in most things except when dealing with change in velocity.
Relativistic mass is special and depends on the relative motion between the objects.
In any case gravitational waves posses invariant mass, so essentially they do have mass, and if you could hold them you could weigh them on a scale.
> since the mass of the photon acts exactly like mass in most things except when dealing with change in velocity
Right: inertia. Funny that.
The fact that photons are affected by gravitational fields, even though they're massless, was a major victory for the theory of general relativity. It wouldn't be a big deal if you could just say the photon has mass. Because it doesn't.
A photon is massless. Fullstop. To say otherwise is to use a nonstandard definition of "mass". At best, people won't know what you're talking about. At worst, they will assume you don't. You should be more specific next time.
You can calculate what the non-linearities do to gravitational waves and, in short, this isn't correct.
I don't know, but my intuition tell me that would lose almost all it's energy as heat, but if there is better information please let me know.
[1] http://news.mit.edu/2015/advanced-ligo-begins-operations-091...
[2] https://twitter.com/LKrauss1/status/647510799678750720