Hard to imagine how engineers, already tasked to prepare for earthquakes, fires, storms, and perhaps collisions, cope with a requirement to deal with the bending of spacetime itself. (Guess I’ll have to go read the link.)

It still seems to me that, say, a supernova shockwave passing through a nebula might leave differently-shaped ripples than would a similar mass of non-relativistic particles, but the experiment would be rather difficult to set up properly.

… wakefields are scattered over very wide areas …

The terminology makes sense, but probably causes some confusion among readers of pre-Victorian English literature.

Thanks for your patience in explaining things to the physics-ly handicapped!

Yes, particles traveling at relativistic speeds produce a kind of space-time shockwave and this is a fact well known by particle collider designers who need to build special buffers and dampeners as they whiz by. I mentioned this in a post about the colliders of the future in which the energies they would create could knock out some of the insanely delicate and expensive machinery.

Relativistic wakefields don’t diffuse gravity because they’re usually generated by tiny particles and while they constantly interact with much larger chunks of matter, they don’t seem to have any serious cosmological consequences as far as we know.

Unlike in colliders where bunches of them are aimed to smash into each other at 0.997c, their wakefields are scattered over very wide areas and the mass of the objects they hit is so immense by comparison, it’s like driving through a field of flies. Sure, some will smack into your windshield and leave a little streak, but it won’t change the direction of your car. The biggest effect cosmic rays have on Earth is the production of short lived muons, close cousins of electrons, in the atmosphere.

If a cosmic “ray”/particle bangs into an atomic nucleus, that nucleus will be all messed up in ways that wouldn’t happen if it met a similar particle at a sedate 0.004c. Well and good, but similar in principle to the difference between being shot and having a little kid throw a bullet at you.

Now imagine, say, a loosely packed dirty snowball drifting free in interstellar space, and a kilotonne iron cannonball zipping by at .004c, passing within 1 mm of the snowball. Gravitational effect is close to zero; maybe a few water molecules shift position slightly.

The next cannonball, otherwise identical, skims the snowball at the same clearance, but 249.9 times faster. If (the weak point here) my understanding of relativity is anywhere near accurate, the spacetime curvature/gravitation pull of this object is significantly greater than that of its slowpoke twin, and its tidal effects on the snowball are detectable.

In reality, my thought experiment is for practical purposes impossible. Nonetheless, even though they don’t travel in unified bodies, the rays/particles emitted by supernovae (etc) amount to exatonnes of mass, multiplied (I think) by the relativistic effect of their momentum. Does that unevenly diffuse gravitational influence (like that of comparably diffuse interstellar hydrogen) have any measurable or theoretical cosmological consequences?

One very important thing to remember is the size of those particles. They’re protons and electrons with some helium nuclei, so their small size and mass inherently limit the effect they can have on the surrounding matter, even when traveling at 0.999c.

Let me step back & take another run at my previous question:

IIRC, an object zipping along at relativistic speeds experiences several counterintuitive effects according to Einstein’s theories. Most attention is paid to time dilation (cuz it’s fun in sf plotlines, and has also been measured), but there’s also an increase in effective mass (or gravitational pull, or spacetime curvature). A stray body passing by at a high fraction of c will alter another body’s course more than one of the same mass and path just ambling along.

Back to our cosmic ray particle, cruising at almost-lightspeed. Its hypothetical mass at rest is, poetically, as close to zero as its actual velocity is as close to c. But does that near-photonic rate of motion give it more influence on material bodies than it would otherwise have – and if so, how much, and what else might that imply?

That’s kind of a tricky question. I think you may be wondering about their momentum more than their mass since they move so quickly because they have very little mass and are thus going close to the cosmic speed limit.

“Does their aggregate mass have notable cosmological consequence?”

And that’s one of the mysteries of modern science. So far, it doesn’t seem so, but who knows how that idea will be refined after the LHC smashes enough particles for us to make a definitive statement about the Higgs boson.

I s’poze “very little mass” is relative, too. How much of their (human-measured) mass is due to their material substance (if that term even applies), and how much comes from their velocity? Does their aggregate mass have notable cosmological consequence?

… 0.004c …

Put that way, it sounds positively boring.

On a micro scale, those would be the particles in cosmic rays which can travel at 0.999c because they have very little mass and are created in energetic events like stellar fusion, supernova explosions, or in the accretion disks of black holes.

On a macro scale, that would probably be RX J0822-4300, a neutron star that was slung around by Sgr A*, the supermassive black hole in the center of our galaxy, and is moving at about 4.8 million km per hour. That works out to around 0.004c.

The descending career paths of Jøm Hurum, the balloon boy, or Britney Spears?

Given all the questions raised by Einsteinian frame-of-reference issues, simply defining stellar velocities seems a bit problematic. F’rinstance, good ol’ Sol is orbiting the galactic center at a respectable clip; add in the galaxy’s motion within the galactic cluster, etc and hang on to your beret! Cherry pick your star, galaxy & cluster, perhaps you could get within an order of magnitude of c.

Leaving out expansion-of-the-cosmos factors for a moment, just what is the fastest-moving known interstellar object?