Well played, Ludovic.
Nice.
Ludovic, for once a clever “zombie” comment on a resurrected thread - good show.
Gin Bell, if I may be so bold as to guess what I think you were asking with your question:
I don’t think your question was specific to neutrinos. I think you were wondering how to wrap your head around something existing, yet having no mass. An excellent question, worthy of a child, which I say as a compliment.
Perhaps the error here is assuming the properties of the every day physical world apply at the micro level. As soon as you get down to subatomic particles, it’s often best to check your intuition at the door and go with what the equations tell you. It’s like a different country down there at the micro level with its own laws - electrons, photos, neutrinos etc. aren’t obliged to obey our everyday “common sense” rules in the everyday world.
Just because in everyday life you’re used to everything having mass, doesn’t mean the same holds true at the subatomic level. You would rightfully assert that, for example, an apple has to weigh something, such as 5 ounces, but you can’t have an apple that weighs zero ounces. At the subatomic level, you can: an “apple” (i.e. photon, gluon) can exist yet have zero mass. At that level, mass is just another “property” like “spin” or “charge” that a particle can have or not have. The latest thinking is that mass itself, as a property, is imbued by the Higgs Field, hence the huge fanfare around the putative discovery by CERN of the Higgs Boson.
Maybe this will help. Forget about mass, and substitute another property: electric charge. It happens that electric charge is a property that objects in the everyday world can either have or not have. (It’s a little more complicated than that, but I’m simplifying.) You can touch a live wire and get an electric shock (DNTTAH!) but then you touch that juicy apple in the fruit bowl and do not get a shock, because it has no (net) electric charge. Would you recoil in horror and conclude that the apple does not exist, because it lacks electric charge? No. The thought wouldn’t even occur to you, since you know instinctively that electric charge is an “optional” property in our everyday world, so an apple doesn’t have to zap you when you touch it in order to exist. The apple can happily exist with no electric charge. So it is with the property of “mass” at the microscopic world.
At least…that’s my lay understanding 
I don’t get it! 
For what it’s worth, photons (and neutrinos and gravitons and the rest) do still have energy, momentum, and angular momentum, even with little or no mass.
How can a particle have momentum when it does not have mass? Is this because they travel at the speed of light?
That’s correct, Gin Bell. Any massless particle will travel at the speed of light, and has momentum directly proportional to its energy.
A particle made of pure energy, such as a photon, isn’t governed by the same laws as matter (i.e. E=mc[sup]2[/sup]).
So, a photon’s momentum is derived from the equation, E=hf, where E is energy, h is Planck’s constant and f is the frequency/wavelength.
I stil can’t grap this in full 
If particles without mass travel at the speed of light, then such particles do not experience spacetime?
Does this mean such particles are at some level present everywhere at once and that’s how to explain ‘spooky action at a distance’ in photon entanglement?
What are current explanations for photon entanglement? Can someone provide a link I may understand?
Let me say another excellent question, worthy of a child, which I also say as a compliment.
Yes, in some sense photons don’t experience spacetime; since they’re moving at the speed of light, from their point of view it takes no time at all to travel from one point to another. On the other hand, they still follow paths through spacetime, so when space is curved by gravity, photons take a curved path, too; in that sense photons certainly do experience spacetime.
But I don’t think it’s useful to think about this relating to entanglement at all. Entanglement is really a quantum thing that happens, and (what some people interpret as) action-at-a-distance is just one little aspect of quantum mechanics. Wheras time dialation and ‘spacetime’ are described by relativity.
And right now, we still don’t know how to integrate quantum mechanics and relativity. If the best physicists in the world treat them separately, you probably should, too.
The way I was seeing it this would only be true if you observe from a point other than the photon itself.
In a personal search for satisfactory explanations of spacetime I decided to look into nuclear decay rates. I found to my surprise that the latest data claims annual inaccuracies in such rates. Getting all exited about this idea I then read on another site that these inaccuracies were simply due to the fact that we only have 3 digit accuracy on such data. Fluctuation was said to be the result of more accurate measurement. I didn’t find this a very satisfactory explanation but couldn’t get my hands on actual data to look into it myself. What are your opinions on this topic?
“Glasstone15 (1950) has the half life for Proactinium 231 as 3.2 x 104 years while Kaplan l6 (1962) has the half life as 3.43 x 104 years. For the half life of Radium 223, Glasstone has 11.2 days while Kaplan has 11.68 days…”
If the radioactive decay rate is slowing down, then speed of light must slow down too.
I see the difference as the result of better measurements, or at least as the result of experimental error. Just from your quote and your previous post, I do not see any indication that decay rates for all materials are decreasing.
I found this to be very logical when thinking about it over and over. Whether readings are inaccurate due to human error or round ups may be beside the point. The real question instead could be whether time is indeed a constant or not. If true than this would drastically impact the way we look at things.
Time isn’t a constant, so we can all sleep well tonight!
I meant speed of light …duh… I wish I could find the edit button, seems newbies are not allowed to edit posts.
Not just newbies… Everyone only gets a 5 min. edit window.
ETA: However, if c were slowing down, things like GPS would begin to fail.