Thread.new is slow

gistfile1.rb

require "rubygems"
require "rbench"

def noop
end

RBench.run(100_000) do
  column :one, :title => "Unthreaded"
  column :two, :title => "Threaded"

  report "Thread.new is slow" do
    one{noop}
    two{Thread.new{noop}}
  end
end

__END__

# Ruby 1.8.7-p302
                           Unthreaded | Threaded |
--------------------------------------------------
Thread.new is slow              0.022 |    8.644 |

# Ruby 1.9.2
                           Unthreaded | Threaded |
--------------------------------------------------
Thread.new is slow              0.013 |   13.448 |