Re: How is it known that the Milky Way is a spiral galaxy ?

jbmorla@xxxxxxxxx wrote in
news:1149057191.397175.197480@xxxxxxxxxxxxxxxxxxxxxxxxxxxx:


Llanzlan Klazmon wrote:
jbmorla@xxxxxxxxx wrote in news:1149050310.985264.243480
@y43g2000cwc.googlegroups.com:


Phineas T Puddleduck wrote:
In article <1149020209.513646.243530@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
<jbmorla@xxxxxxxxx> wrote:

Hi,
I'm an absolute newbie
I just wonder how light propagates 13 billion years to hit our
retin
a,
through void, with nothing to prop against?
And as in a crime novel, "cherchez la femme", if you look at the
universe, it's packed with light no matter
where you go, why is light so meaningful to understand the system?

De la discussion jaillit la lumière

Ishke Baha


Light is a self-propagating electromagnetic wave, and unlike sound
waves doesn't need a medium to wave against, per se. Light is a
electric and magnetic wave at right angles to each other, and to the
direction of motion.

The universe is currently dark energy dominated, but was matter
dominated and in the early days was radiation dominated. A quick
readup on the cosmic microwave background would give you a good
starter to cosmology.

--
The true enemy of science is psuedoscience...

Hi,
Light is a self-propagating electromagnetic wave
How can it propagate without consuming energy?

Newton's first law of motion:

Every object in a state of uniform motion tends to remain in that state
of motion unless an external force is applied to it.

As long as the photon doesn't interact with anything else it continues
on its' merry way.

The erroneous belief that things come to rest unless a force is
applied, was debunked by Galileo. A force is required to change the
state of motion as stated by Newton. The source of the error is that we
are used to things being slowed down by mechanical friction, air
resistance etc.

I thought there was no such thing as perpetual movement

You thought wrong. You are probably confused with perpetual motion
machin
es
of the first and second kind.

Klazmon.




<SNIP>

Hi,

Newton's first law of motion:

Every object...

So you consider light is an object?

You stated:

"How can it propagate without consuming energy?
I thought there was no such thing as perpetual movement"

I pointed out that the belief that propagation requires consumption of
energy is erroneous.

Case closed.

Klazmon.

<Nonsense snipped>
.

Relevant Pages