NowThatWeKnow

if you shine a lot of light onto a reflective surface, would the reflective surface be pushed back by the light? From the photons hitting and bouncing off it?

Solar sails come to mind so I think yes.

http://en.wikipedia.org/wiki/Solar_sail

I back up everything important on a CD along with other methods. Not sure about Solar flare damage but a close lightning strike can damage an unplugged computer.

I'm sorry... it was so bad I kept falling asleep and never really could give you some detailed analysis of it... deleted it pretty fast!

 

Didn't know this thread was based on a particular program viewing?

I will agree that a few episodes were lame but some were pretty good. My least favorite was "Sex in space" and "Parallel universes" was pure speculation. The Light speed episode along with a few others were pretty good IMO

Anyway.. Martin, I was about to start a thread when I saw your post about the cosmological expansion (or cosmological redshift etc.). (And hey, these questions are laymen , not technical as such).

 

I am thinking.. we see light from for example andromeda.. no strike that for simplicity lets say a star in our galaxy.. 10 000 ly away. (and let us just say it is moving away from us, the principle is important, not the actual dynamics of the galaxy.. we could use a redshift galaxy as an example). Anyway.. light reaches us now, and so when we say.. hey this thing is 10 000 years away.. is that AFTER taking into account it was perhaps 7000 ly away when the light started reaching us or was it 10 000 at the time the light was emitted and so now would actuall be, lets say 11000 light years away?

The Ned Wright calculator can answer your questions but it deals better with billions of light years, not thousands.

http://www.astro.ucla.edu/~wright/DlttCalc.html

The numbers you are talking about are still in the Milky Way and the cosmological expansion does not apply.

Most of the experts around here will argue that light can not be slowed down but the average speed can be slowed down as it passes through different substances. The light is absorbed and then re-emitted with a delay coming while it is absorbed.

That being said, here is how to stop or slow down light.

http://www.hno.harvard.edu/gazette/2001/01.24/01-stoplight.html

so for example, if you drive a rocket ship at the speed of light to the sun and back, the trip will be instanteneous. It won't take distance/(speed of light) time, it will take 0 minutes.

Actually it takes over 8 minutes for light to reach us from the Sun.

I just downloaded some THC documentaries in cluding some on space... more amateur , crap documentaries I have never seen. Stay well clear of that channel!!! (don't know how it is on archaelogy and the like though but certainly is C R A P on anything in physics).

I think calling THC "C R A P" ("The Universe" program in particular) is a little unfair. It was not designed to meet the physics experts expectations for continued education. It is for the amateur and attempts to convert the math into words so normal people can understand and enjoy cosmology and relativity to some degree. Just like her in SFN, the History channel "The Universe" program presents facts and speculation and I have no trouble separating them considering their presentation. I would like you or anyone else to point out something presented as fact during "The Universe" program that was not in the ball park. I think it does well in getting people interested so they can continue their education using different avenues if they choose. You can't call kindergarten "C R A P" just because it is below your level. Accept it for what it is. Those are my thoughts.

Careful, though, because in the Hafele-Keating experiment, the two directions are not the same. The earth is not an inertial reference frame, so east- and westbound travelers are not going the same speed, even if their speed with respect to the earth's surface is the same. You have to do the comparison with respect to an inertial frame.

Yes, everything would have to be equal relative to an inertial frame. After reading http://en.wikipedia.org/wiki/Hafele-Keating_experiment I see that GR was considered.

Yup. That's the Hafele-Keating experiment:

http://en.wikipedia.org/wiki/Hafele-Keating_experiment

That video made it sound like only SR was considered and not GR because of altitude.

but people dont seem to realize this. many people (without a firm understanding of relativity perhaps?) seem to think that time travel is impossible, yet it clearly is not so.

Gravity and speed (acceleration) cause clocks to to tick at different speeds so we are all traveling through time, but some at different rates. This could put you into someones future but not their past.

Merged post follows:

do both the planes get their watches behind? despite their direction?

Yes, if the trips were the same as far as acceleration, speed and time.

How do you combine the meters cubed and km squared?

Wouldn't [math]125,000m^3 = 125km^3 = 1,953,125km[/math]

There is an energy conversion calculator that will convert Joules to just about anything at:

http://www.cthreepo.com/cp_html/math1.htm

are you sure there? maybe nothing weve come across, but it seems that all the data other than the amount directly containing what weve tooken from space regarding this idea seems to suggest there should be. maybe its just undetectable so far.

It seems most experts agree that space is just a metric but there are a few that think there may be an ether that has not been defined yet. Nobel Prize winner Frank Wilczek calls it a grid "But the Grid is highly evolved ether,

ether on steroids if you like, with many new features."

So then gravity does effect time in a noticeable difference?

It depends on what you call noticeable. (GPS satellite - Altitude 12,000 miles) Our Earth clocks are slower by 45 microseconds per day. It would take a black hole to be really noticeable. When Martin said "The pendulum clock at the top of a tall building would run slower than his brother on the ground floor because of less pull on his pendulum." He was referring to a pendulum clock only. Normally less gravity will cause a clock to run faster.

Every post you've made at this site is a trolls post.

I agree.

I am traveling at .5c towards you. I turn on a light aimed at you.

 

In one second, how far did the light travel? 186,000 miles? OK

 

How far did I travel in that same second, 93,000 miles? Good.

 

The light is ahead of me 93,000 miles in one second.

 

The light is 186,000 miles closer to you in one second.

 

I am 93,000 miles closer to you.

 

The light appears to be traveling at .5c away from me from my perspective, as in the one second duration, the light goes from me to 93,000 miles in front of me. That means my perception (illusion) is that the light is traveling at .5c.

...

You will see the light moving away from you at 186,000 miles per second.

I think that what you are not considering is time dilatation. Relative to your starting point it will seem to you that the light is moving at 1.5c but your clock is running slower then the person it is pointed at. 1 second for you will be more then one second for the other person so relative to their time light is moving at c.

Yes, and a shorter trip could make you younger then your kids when you get back. It will seem as time is passing as usual for all concerned.

you could just see what the clock says for you, and add the amount of time it would take the light to reach you from it, judging by yours and its coordinates. get the right time, i think.

The right time on Earth but not your right time. I think.

What do you mean by "twin paradox" mate?

The twin paradox

http://www.phys.unsw.edu.au/einsteinlight/jw/module4_twin_paradox.htm

Another example is that if you were in a rocket with 1 G continuous acceleration, your could cross the galaxy in about 12 years on your clock but on Earth well over 100,000 years will pass.

Check out the "Long Relativistic Journeys" calculator at the bottom.

http://www.cthreepo.com/cp_html/math1.htm

Accounting for 50% of variation is not the same thing as "changing your intelligence by 50%."

Point taken. My reply was also referencing post #9 "50% genetically determined is plenty for natural selection to work with." and my wording could have been different.

Honestly, I just don't think we're anywhere near where we need to be to begin drawing real conclusions.

 

To be cynical, we're trying to estimate the heritability of a poorly-defined trait probably controlled by many, many genes and regulatory regions using fairly small sample sizes. No part of that is conducive to getting answers.

I present planet Earth as our laboratory. Watch a group of people in their original environment and then watch them over generations in the USA environment. The pecking order does not change.

This method escapes the problems of interminably debating how accurate IQ tests are. While you could argue that the above measures are only indicative of intelligence, you cannot argue that what they measure is meaningless, since they are direct physical measurements. Good science!

Good science would have gone well beyond using just twins. I would like to see a chart something like in the "Bell Curve" book.

...but by no means all of it. Roughly half of the variation between two individual's intelligence is due to genetic differences between them, and the remainder to the details of their upbringing.

Regardless of their upbringing, there are some that have trouble making it past Chimpanzee intellect. It is important to consider the difference in one's ability to learn and one's ease of learning. You may be capable of learning by rote or by understanding. Your upbringing my help determine what you know but changing your intelligence by 50% is stretching it IMO.

Isn't "genetically determined" what makes evolution and natural selection possible? My observations tell me it plays a larger roll than many would think.

If the universe only exsits "now" this must be uniform for all in it.

I was wondering how long it would take for "now" to show up.

I think Swansont explained it well earlier in this thread.

"The confounding thing about relativity is that it's not just a static offset of times, but that clocks run at different rates. We could agree on a universal time if we chose to, by picking a single reference frame and do the relativistic conversions, but there is no physics reason to prefer one over the other."

Mod note: this and other recent posts moved from another thread

Sleeping works better then "twiddling your thumbs" for me.

A relativistic trip can take you to the future, as shown by the 'twin paradox'.