[thamer]

It took a few tries, but I got Wolfram Alpha to compute its velocity compared to the speed of light[1].

I started with:

    sqrt(1-((1/(1+120 PeV / (neutrino mass * c^2)))^2))

but it simply said "data not available". So I changed:

    120 PeV to 120e15 * 1.602176634e-19 kg m^2 s^-2
    neutrino mass to 1.25e-37kg
    speed of light to 299792458 m/s

and finally it gave a numeric result:

    0.999999999999999999999999999999999999829277971

(that's 36 nines in a row). Pasting it in Google says the value is "1", which is… not far off.

If you want details about the way this is calculated, I dug up the formula from an article I'd written about particle velocities in the LHC, back in 2008[2]. For comparison, their 7 TeV protons were going at 0.999999991 × c.

[1] https://www.wolframalpha.com/input?i=sqrt%281-%28%281%2F%281...

[2] https://log.kv.io/post/2008/09/12/lhc-how-fast-do-these-prot...

[davrosthedalek]

We don't know the neutrino's masses, so this is a lower limit for v (since the mass you used is an upper limit)

[dr_dshiv]

That’s fast! But for how much energy? For comparison, the total energy from this one particle (0.0192 joules) is equivalent to keeping a 50 mW LED lit for a third of a second.

[wd776g5]

I can see it came from your source but why is the neutrino mass specified in kg instead of g? why not 1.25e-34g?

[thamer]

The kilogram is the base unit of mass in the International System of Units (SI): https://en.wikipedia.org/wiki/SI_base_unit

Time is in seconds, length in meters, temperature in kelvin, etc. A unit of energy like a joule is then defined using these base units, so 1 joule is 1⋅kg⋅m^2⋅s^-2.

[l33tman]

In particle physics you just use GeV (with varying powers) for most parameters :)