Ask a physicist anything. (7)

[Chalnoth]

What are your thoughts on the superluminal velocities of muon neutrinos reported by OPERA?

Highly highly unlikely to be correct. We already have a far more sensitive measurement of the speed of neutrinos, one that is far less prone to error: the measurement of neutrinos from SN1987A. At 180,000 light years away, we don't need sensitive clocks to detect the arrival time difference, and the result is that the speed of neutrinos and light differs by no more than roughly one part in a hundred million, if you are exceedingly generous about the systematic errors.

The OPERA detection has neutrinos going faster by one part in a hundred thousand, using an instrumental setup that is extremely hard to do. So the best bet is on an experimental error.

 

[Non sequitur]

Highly highly unlikely to be correct. We already have a far more sensitive measurement of the speed of neutrinos, one that is far less prone to error: the measurement of neutrinos from SN1987A. At 180,000 light years away, we don't need sensitive clocks to detect the arrival time difference, and the result is that the speed of neutrinos and light differs by no more than roughly one part in a hundred million, if you are exceedingly generous about the systematic errors.

The OPERA detection has neutrinos going faster by one part in a hundred thousand, using an instrumental setup that is extremely hard to do. So the best bet is on an experimental error.

A 0.0025% increase is rather small.

 

[Chalnoth]

A 0.0025% increase is rather small.

Depends. It's humongous when compared to the error bars on the neutrino speed as measured by SN1987A.

 

[Non sequitur]

Depends. It's humongous when compared to the error bars on the neutrino speed as measured by SN1987A.

True, true.

It'll be interesting to see if anyone comes up with some concrete evidence how it was faulty, instead of falling in the "well, that obviously can't be true" pile.

It's just as interesting to see things proven wrong as right.

Go science!

 

[Chalnoth]

True, true.

It'll be interesting to see if anyone comes up with some concrete evidence how it was faulty, instead of falling in the "well, that obviously can't be true" pile.

Oh, yeah, there's definitely a lot of work being done right now to try and replicate the result. We'll probably know the answer within a couple of years.

 

[Cactus Jack]

Ask a physicist anything.http://www.christianforums.com/t7558609

What is the likelihood of using planetary rotation to perform time travel?
In this, let's say you hop in a SR-71 Blackbird and fly east or west greater than the speed of sound, for 24 (or longer) hours. What prevents this from happening? Other than the lack of fuel?

 

[Chalnoth]

What is the likelihood of using planetary rotation to perform time travel?

Zero.

In this, let's say you hop in a SR-71 Blackbird and fly east or west greater than the speed of sound, for 24 (or longer) hours. What prevents this from happening? Other than the lack of fuel?

The human conventions of time cannot possibly lead to time travel. That's like saying you can travel back in time by constructing a clock that ticks backwards. Otherwise you could go back in time simply by going to the north or south poles and walking in circles around the north/south pole. The idea is pretty ludicrous.

In order to keep clocks sensible around the world, the international date line corrects for the date difference. Going west across a time zone boundary makes you set your clock back by one hour. But going west across the international date line causes you to move to the next date on the calendar. So go all the way around the world and your clock goes to down 24 hours, one for each time zone, and also up 24 hours as you cross the international date line, leading to no change once you arrive back at your destination.

 

[Wiccan_Child]

What is the likelihood of using planetary rotation to perform time travel?

In this, let's say you hop in a SR-71 Blackbird and fly east or west greater than the speed of sound, for 24 (or longer) hours. What prevents this from happening? Other than the lack of fuel?

Nothing prevents it - it's perfectly possible to travel faster than sound for 24+ hours due east (or west). Eventually, you'll cross the International Date Line and your date will flip back or forward, but that's a matter of notation than actual time travel.

A common misconception is that, in the Superman film, Superman flies around the world so fast that he reverses its spin and thus reverses time. In fact, what he's doing is this: he needs to go back in time, so he travels really really fast. But he has to stay near the Earth, so he travels really fast around the Earth in an orbit. So, when time reverses, it looks like he's causing the Earth to rotate backwards - but in reality he's just travelling backwards through time.

I don't know if that's relevant to your question, but, in short, no, travelling for long periods of time east or west won't make you travel forwards or backwards in time.

 

[Davian]

Nothing prevents it - it's perfectly possible to travel faster than sound for 24+ hours due east (or west). Eventually, you'll cross the International Date Line and your date will flip back or forward, but that's a matter of notation than actual time travel.

A common misconception is that, in the Superman film, Superman flies around the world so fast that he reverses its spin and thus reverses time. In fact, what he's doing is this: he needs to go back in time, so he travels really really fast. But he has to stay near the Earth, so he travels really fast around the Earth in an orbit. So, when time reverses, it looks like he's causing the Earth to rotate backwards - but in reality he's just travelling backwards through time.

I don't know if that's relevant to your question, but, in short, no, travelling for long periods of time east or west won't make you travel forwards or backwards in time.

That's always an interesting tidbit left out of time travel stories. To go back in time, you will have to travel to where earth *was*.

 

[pgp_protector]

That's always an interesting tidbit left out of time travel stories. To go back in time, you will have to travel to where earth *was*.

 

[acropolis]

That's always an interesting tidbit left out of time travel stories. To go back in time, you will have to travel to where earth *was*.

The lack of an absolute reference frame really compounds this problem.

 

[pgp_protector]

The lack of an absolute reference frame really compounds this problem.

So True
Rotation of the earth is (depending on Latitude) 0-1K MPH
Earth's Orbital Speed (App) 66K MPH
Milky Way's Orbital Speed (App) 483K MPH
Milky Way's Relative Speed to the CBR 1.3M MPH
so a 1 Second Jump back it time would be .. well... not good
You could (depending on Direction of Travel up to 400 Miles away from where you were )

 

[Wiccan_Child]

So True
Rotation of the earth is (depending on Latitude) 0-1K MPH
Earth's Orbital Speed (App) 66K MPH
Milky Way's Orbital Speed (App) 483K MPH
Milky Way's Relative Speed to the CBR 1.3M MPH
so a 1 Second Jump back it time would be .. well... not good
You could (depending on Direction of Travel up to 400 Miles away from where you were )

The whole frame of reference thing is weird - on the one hand, the Earth was clearly in a different place the further back you go. On the other, where would it be? Suppose you did go back in time, and you noticed the Earth was somewhere other than where you were - ipso facto, you have just defined an absolute frame of reference, thus unravelling all of Relativity.

Thinking about it, the only way to avoid inferring an absolute reference frame is if you reappear only where the time machine exists - i.e., you can't go back before time machines were invented, specifically your time machine.

Which also solves the Temporal Tourist paradox.

 

[Gath]

Ok, two questions for you:

1. If you had a spacecraft flying away from earth at 99.9% of the speed of light, (let's assume it's already 1 light year away) and you wanted to send a message to it from earth, (via radio waves at the speed of light) would you be able to in a reasonable amount of time? I'm fairly certain that it would take an incredibly long time to reach the spacecraft relative to earth, because relative to earth the message is traveling towards the spacecraft at .1% of the speed of light. However, relative to the spacecraft, it is traveling at the speed of light towards it. How long would it take then, relative to the spacecraft? 1 year, for the 1 light year? That would be my guess, because the spacecraft is not moving relative to itself and the message is moving towards it at the speed of light. Am I correct in that thinking?

2. This one's a bit stranger. Let's assume that the Big Bang made, literally, a big bang. That is to say, it made a lot of noise when it started expanding. Because sound travels slower than light, the sound would therefore not be at the very edge of the universe. (not literal edge, but the extent to which it has expanded so far.) Does that mean that it would be possible to fly a spacecraft out beyond the point that the sound waves had reached so far and hear the big bang? If not, where did I go wrong?

Thanks.

 

[Chalnoth]

Ok, two questions for you:

1. If you had a spacecraft flying away from earth at 99.9% of the speed of light, (let's assume it's already 1 light year away) and you wanted to send a message to it from earth, (via radio waves at the speed of light) would you be able to in a reasonable amount of time? I'm fairly certain that it would take an incredibly long time to reach the spacecraft relative to earth, because relative to earth the message is traveling towards the spacecraft at .1% of the speed of light. However, relative to the spacecraft, it is traveling at the speed of light towards it. How long would it take then, relative to the spacecraft? 1 year, for the 1 light year? That would be my guess, because the spacecraft is not moving relative to itself and the message is moving towards it at the speed of light. Am I correct in that thinking?

Right, so, it can take a little while to get there from the perspective of us on Earth (999 years if I'm thinking about this problem correctly). But it won't take very long at all from the perspective of the space-craft, because of the combination of time dilation and length contraction. At v=0.999c, the time dilation factor is 22.37. So that 999 years to us is 999/22.37 = 44.67 years to them.

How does this work out? Well, in addition to time dilation, there is also length contraction. We not only see their clocks moving more slowly, but they see the distance between them and the Earth as being much closer. Closer by the exact same factor of 22.37. That is, when we measure them moving away from us at 0.999c at one light year away, they see themselves moving away from Earth at 0.999c at 1/22.37 = 0.0447 light years away. So it takes, from their perspective, 999*0.0447 years for the message to arrive, or 44.67 years.

2. This one's a bit stranger. Let's assume that the Big Bang made, literally, a big bang. That is to say, it made a lot of noise when it started expanding. Because sound travels slower than light, the sound would therefore not be at the very edge of the universe. (not literal edge, but the extent to which it has expanded so far.) Does that mean that it would be possible to fly a spacecraft out beyond the point that the sound waves had reached so far and hear the big bang? If not, where did I go wrong?

Well, there are two things wrong with this:
1. The big bang happened everywhere, so the sound is all around us.
2. Noise doesn't transmit through the vacuum of space, so we can't hear it now anyway.

However, the universe wasn't always as spread-out as it is now! Sound waves transmitted just fine in the early universe, and in fact there were a lot of sound waves early-on! See here:
Listening to the Big Bang : Starts With A Bang

 

[Cactus Jack]

Nothing prevents it - it's perfectly possible to travel faster than sound for 24+ hours due east (or west). Eventually, you'll cross the International Date Line and your date will flip back or forward, but that's a matter of notation than actual time travel.

A common misconception is that, in the Superman film, Superman flies around the world so fast that he reverses its spin and thus reverses time. In fact, what he's doing is this: he needs to go back in time, so he travels really really fast. But he has to stay near the Earth, so he travels really fast around the Earth in an orbit. So, when time reverses, it looks like he's causing the Earth to rotate backwards - but in reality he's just travelling backwards through time.

I don't know if that's relevant to your question, but, in short, no, travelling for long periods of time east or west won't make you travel forwards or backwards in time.

Actually, it's kinda like that, I think. If the earth rotates at 1k mph, and you fly against the rotation at at least twice that, in theory you only fly for 12 hours to reach your destination. I dunno. In my mind it all works out.

 

[Chalnoth]

Actually, it's kinda like that, I think. If the earth rotates at 1k mph, and you fly against the rotation at at least twice that, in theory you only fly for 12 hours to reach your destination. I dunno. In my mind it all works out.

Well, yeah. But getting to another location in 12 hours still takes 12 hours. It'll still be 12 hours later no matter which way you slice it.

 

[Zippy the Wonderslug]

This is being predicted for tomorrow.

Possible tornadoes include the following:


AL north - 5
AL central (night) - 3
AR east, north-central - 3
GA north (night) - 3
IL south - 4
IN south - 4
to 5 KY central - 7
KY west - 4
KY east - 6
LA north - 3
LA central, southeast (night) - 3
MO southeast - 3 to 4
MS north - 5
MS central (night) - 3
NC west (night) - 3
OH - 3
TN north-central - 7
TN west - 4
TN east - 5 to 6
TN south-central - 5
WV west - 4
Other areas - less than 2

This seems awfully strange for being so early in the year.

I'm still kind of waiting for winter to finally hit my State.

Are there any theories or studies showing that this could be a really big year for natural disasters?

Cheers guys.

 

[Chalnoth]

Are there any theories or studies showing that this could be a really big year for natural disasters?

Well, I think it's generally pretty difficult to predict the weather on time scales of a year or two. However, we do know that global warming is causing the average rate of severe weather, including both storms and droughts, to increase.

 

[Cactus Jack]

Ok. Mr. Physisisicist- Pheromones. Some businesses (such as Ahtenainstitute.com) sell pheromone fragrances to attract the opposite sex. Does this really work and if so, is the use of such considered ethical in mate selection?