Are there any particles or "cosmic rays" in space that travel at
substantially less than the speed of light?

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Request for Question Clarification by wengland-ga on 14 Jun 2002 15:15 PDT

Particles?  Sure.  Dust.  Everywhere.

Or high energy particles that exhibit both wave and particle behavior,
like photons?

Please clarify what you are looking for.

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Request for Question Clarification by mvguy-ga on 14 Jun 2002 16:01 PDT

Are you interested in theoretical subatomic particles, or only those
whose existence has been demonstrated?

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Request for Question Clarification by gnovos-ga on 14 Jun 2002 18:03 PDT

Well, I'm not 100% sure this question is answerable, as "travel at
substantially less than the speed of light" is not clarified with what
frame of reference you wish to measure a particles speed.  What I mean
is, foe example, if you are measuring from a point outside our galaxy,
the earth will appear to be moving quite fast, but measuring from it
from the moon would give you a speed signifigantly less.

I think your question needs some deeper thought before we can answer
it honestly.

The short answer to your questions is "yes."

As wengland-ga points out, there are dust particles traveling at a
wide variety of speeds.  Depending on how big something that meets
your definition of "particle" can be, meteors are another example. 
The question of cosmic rays is answered directly at
http://helios.gsfc.nasa.gov/qa_cr.html#crvel:  "The velocity of cosmic
rays can go from a small fraction of the speed of light up to about
.999999999999 times the speed of light."

This is all dependent on your frame of reference, of course.  The
question of how fast a particle of matter is moving, be it a cosmic
ray or otherwise, is meaningless without a frame of reference.  Any
particle of matter has zero velocity in its own rest frame.  By
contrast, one can always choose a frame of reference in which a
particle of matter is moving at 99% of the speed of light if one
chooses.

Assuming you are thinking of the reference frame of an observer on the
earth, the answer to your question is still "yes."  Cosmic rays and
other particles can travel through space at a wide variety of
velocities relative to the earth.  I think that the solar wind would
be a good example to answer your question with.

"Solar wind is the plasma of charged particles (protons, electrons,
and heavier ionized atoms) coming out of the Sun in all directions at
very high speeds -- an average of about 400 km/sec"  (Source: 
http://helios.gsfc.nasa.gov/sw.html.)  Accord to this page the range
of velocities is anywhere from 300 km/second to 800 km/second.  Rice
University has a really cool page called "Space Weather Resources" at
http://space.rice.edu/ISTP/#RT.  It has real-time data about the solar
wind including speed at http://space.rice.edu/ISTP/dials.html. 
According to this web site, as I write this answer the current solar
wind speed is about 350 km/second.  Since the speed of light is about
300,000 km/second, the solar wind serves as a good example of
“particles in space that travel at substantially less than the speed
of light.”

FYI, here is a little more information on cosmic rays.  The exact
definition of "cosmic rays" is not completely agreed upon.  A good
general definition is that cosmic rays are, "Particles [of matter] and
high-energy light that bombard the Earth from anywhere beyond its
atmosphere."  (Source: http://helios.gsfc.nasa.gov/cosmic.html.  This
web site is also a very good starting point for more information.) 
Many people do not consider photons (light) to be cosmic rays.

Dictionary.com also has a good definition of cosmic rays:
http://www.dictionary.com/search?q=cosmic%20ray.

I hope this helps.

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Clarification of Answer by 8ball-ga on 15 Jun 2002 02:41 PDT

My first link seems to have posted incorrectly.  The trailing ":"
should not be part of the link.  It was meant as punctuation.  Instead
it should be:

http://helios.gsfc.nasa.gov/qa_cr.html#crvel

Sorry for any confusion.

Clarification

To 8ball-ga and other who have commented on my question my regrets at
having left unspecified the nature of the particles of interest. The
particles I was alluding to  were subatomic particles, especially
ionized particles that have been hypothesized as having the capacity
to damage protoplasmic cells. So then the human body, say, may serve
as the frame of reference for the speed of these particles. Such
particles traveling at the speed of light would have a very short
residence time within whatever or whomever it might impinge upon. Call
the impingee me. My idea was that if such particles happened to be
moving with somewhere near the same speed and direction that I was
traveling (with respect to some very distant point of reference) the
particles' residence time within me would be lengthened according to
the degree of match. The longer the residence time, the better chance
of causing mischief, I would assume. Does such a thought have
heuristic value?

I thank 8ball-ga for his quick and thorough anwers.

 Arminius-ga

"Residence time" might not be the best way to think about this.  That
would be OK if there were no interactions, but if there were no
interactions, you wouldn't have to worry about damage.  Kind of like
the old joke that it's safe to run a red light if you do it at very
high speed, because the faster you're going, the smaller the time you
spend in the intersection!

The ionized particles cause damage by virtue of their speed.  If
you're above the protective influence of Earth's atmosphere & magnetic
field, those particles can cause some real damage. Of course, you'll
be in a spaceship, so that will eliminate most of your worries.