Janus

7 hours ago, Moontanman said:

We hear about so called "islands of stability" in super heavy elements, what does this mean exactly? Can we really expect super heavy stable elements or are we talking about elements with half lives more like minutes or hours instead of nanoseconds? 

It's the second case.  Elements that aren't stable, but relatively more stable than you would expect for such a heavy element.

14 hours ago, iNow said:

On the same topic:  A reporter in a recent press conference asked whether Biden would hang a portrait of Trump in the White House ( something Trump refused to do for Obama) and along the same lines would he be inviting Obama to ceremony to finally hang his portrait.  The answer was that no portraits hangings had been scheduled yet. 

But it struck me as a bit of a silly question.  With everything on his plate right now, I doubt that Biden is giving much thought (or should be) to such purely ceremonial things. 

17 hours ago, iNow said:

What an excellent and entirely valid / relevant observation. Many may be leaving to push rightward toward the “Patriot Party.”

Registrations to the GOP surged in many states when he won the primary in 2016. People wanted to join “the Trump Party!” and many of them are likely now just reverting back to their previous baseline state. 

On the other hand, there are a number of past members of former Republican administrations that have begun to discuss forming an Anti-Trump party over their dissatisfaction over how the present Republican establishment have been too subservient to Trump.

The party could be bleeding voters from both ends. 

1 hour ago, Col Not Colin said:

 Hi again.

  You could start another thread for what is another topic - but it's your call.

Greatest contribution to cosmology?    The Hubble Law.  Obviously,  just one opinion.

I would put into consideration a different contribution made by Hubble prior to his Law.  In 1924 he discovered Cepheid variable stars in Andromeda, which he was able to use to show that Andromeda was far outside our own galaxy, and not a part of it.   While there had been debate about this., his observations were the first to provide exidence that the cosmos was much more vast than previously suspected and extended well beyond the Milky way.

3 hours ago, wildie9 said:

Hi all, im not a physicist, but have an interest. Now given that most agree in the big bang theory, means everything is moving away from each other in a ever expanding universe. That being the case how can the milky way galaxy be going to crash into the Andromeda galaxy? Albeit in a few years time. 

Just to build on what has already been said.  "Everything" is not moving away from each other.  The atoms making up the Earth aren't, The planets are not moving away from the Sun (or at least not due to reasons tied to universal expansion),  the stars in the galaxy aren't flying apart...

All these structures are held together by interactions that are much stronger than universal expansion.*  Our galaxy, along with Andromeda and a few others are part of a local group bound together by mutual gravitation.   Our local group is one of many in a larger cluster.  You have to go to scales beyond that for expansion to take hold.  So when we say that the expansion of the universe is causing galaxies to move apart, what is really is that the larger bound clusters are moving apart from each other.

* One way of imagining this is to think of yourself as standing on a polished tiled floor in you stocking feet. The tiles are expanding so that the center of the tiles move apart. But the bottoms of your feet, being held together by molecular force, don't expand along with them.

If you have a friend on an adjacent tile he, would, over time, move further and further away from you as the floor expands.  Unless: You reach out and grasp hands. Now, as long as your grip is stronger than the friction between your feet and the floor, you will stay the same distance apart. Gravity acts like your grasped hands. The difference is that gravity gets weaker over distance.  So, as long as galaxies are close enough to each other, gravity can keep them bound together, but when they are further part,  it can't.

4 hours ago, jajrussel said:

Aether, I know it doesn’t exist. My question is about why we know it doesn’t exist. The Michelson-Morley experiment. Which actually as I read about it doesn’t really make sense to me because if c is c invariant what exactly were they looking for? But, Einstein’s c invariant was after M&M, okay that lines up. Hmm, but what other proofs were being looked for? 
 

why was Aether assumed stationary?

 If they expected it to be stationary, why were they assuming a variation of c would be found? I would assume that a stationary system would have to be non-reactive.

the reason I ask is because I was watching a video about dark matter, and dark energy and the reasons they are believed to exist and the reasons why they are called dark. So, we can see the reasons we think they do exist. Then I’m wondering, why did they think Aether existed, originally?  What were they looking for to prove Aether existed?

What would be the difference between an Aether that doesn’t  react with light and matter, accept gravitationally, and dark matter?

 Was the M&M experiment based solely on an expected variable c?

Thank you. 

The M&M experiment assumed that light's speed was fixed at c relative to the aether.   It was an attempt to measure the Earth's motion with respect to the aether. (the aether would be the standard by which "stationary" would be defined.

Now it was possible that, due to other various motions, the Earth, at a given moment, could be stationary with respect to the aether.  However, that could only happen at one particular point of Earth's orbit.  Do the experiment again 6 mo. later, and the Earth's motion with respect to the aether would have to be in the order of 60 km/sec.

If there was an aether that light traveled at c with respect to, the experiment should have have been able to measure some motion of the Earth with respect to it simply by doing the experiment at different times of the year.

54 minutes ago, michel123456 said:

 

 

How?

Assume the object passes at a distance of 1 light sec from you.  When is is at a point just a bit shy of being even with you light leaves it, and takes just a bit over 1 sec to reach you Eye.

A moment later, it is the same distance past the point of being even with you. The distance between it and you is the same distance as it was during the previous moment, So the light leaving it at this moment takes the same amount of time to reach you.  Since the propagation delay is equal in both positions, time time difference between you seeing the object at each position is equal to the time it took to move between the two positions. You can measure the angle between these two sightings, and knowing the closest approach distance (1 light sec), you can work out how far the object moved in that amount of time. 

There would also be a "double image" effect.

For example, assume the object again passes at a minimum distance of 1 light sec from you.  But this time it starts at a point 1 light sec from the point of closest approach and is moving at ~ 2.415c.  The light leaving it at that moment takes ~ 1.414 sec to reach you.  In 0.414 sec at 2.414c, the object will reach the closet approach point, and the light leaving it then arrive at your eye 1 sec later, or 1.414 sec after it was 1 light sec from this point.  In other words, the light that left it when it was 1 light sec short of closest approach, and the light light that leaves it at closest approach both reach your eye at the same moment.

3 hours ago, Ayden said:

How can we know that nothing travels faster than the speed of light (3 x 10^8 m/s)? If there were certain physical phenomena that could travel faster than light, we wouldn't be able to perceive it, since light has a limited fixed velocity.

What makes you think this?

The fact that the object itself is traveling faster than c would not prevent us from seeing it.  Imagine that it is passing by you at a right angle to your line of sight.  Some of the light emitted  by the object just before it is even with you is emitted at nearly a right angle to its path and reaches you. as light travels at c(relative to you) no matter what the speed of the object that emits it.

Some the light emitted by the object just after it passes you is also emitted at an angle so that it reaches you.  Basically this means that as it passes you, you will still see it move across your line of sight.  By using its distance from you, and the speed it appears to cross your line of vision, you would be able to work out that it is moving greater than c with respect to you.

4 hours ago, Danilo_Rocha2 said:

Dark Matter is approximatly 85% of our universe, we don't know what it is so we can´t say that is matter.

But imagine if Dark Matter was a distortion in the space-time fabric and those distrotions were grooves left by stars, planets or even galaxies, that were doing their thing and just did it.

If dark matter was an effect caused by visible matter like stars and planets etc. , then its effects would follow a pattern that reflects that. 

Galaxies would act as if they had extra mass, but that extra mass would be concentrated where we see stars, etc.   However, what we see is that galaxies behave as if most of the mass is located in regions where we see mostly nothing. (Such as the areas above and below the visible disks of spiral galaxies.) So it the distribution of the extra gravitational effect and not just an increased magnitude.

In addition, we have seen examples where the gravitational effect attributed to dark matter has been dislodged from its parent galaxy cluster by a collision between two such clusters. Again if dark matter was just an additional effect caused by the stars, etc by themselves, you wouldn't be able to " knock it loose" from those stars.

We also have found galaxies that are nearly identical in all other respects, but one behaves like it has dark matter, while the other behaves like it has little to no dark matter.  If dark matter was an effect caused by the stars in the galaxy, then two identical looking galaxies would behave exactly alike.

1 hour ago, iNow said:

We now see the Oregon Republican party joining in the condemnation... the question is whether this does more to condemn themselves or the target of their ire.

 

 

  How far the Oregon Republican party has fallen from the days of the likes of Tom McCall and Mark Hatfield.

Or how about "Bernie at 20,000 ft" ( This one was suggested by my Wife)

1 hour ago, studiot said:

Generally an excellent explanation, +1,

but your examples need updating somewhat.

Both these examples were used in 1930's electrical equipment but have long since been abandoned as wasteful of power and potentially dangerous as they result in the excessive generation of heat.

https://electronics.stackexchange.com/questions/252352/setting-heat-on-electric-stove

 

Electronerd, are you sure you meant a bridge rectifier ?

There are many sorts of bridges, but a simple bridge rectifier is not directly comparable to a rheostat.

A bridge is a particular sort of circuit configuration containing four circuit components arranged in a 'diamond pattern.

Some bridges are used for power control. This application would be comparable to using a rheostat for this purpose, but much more efficient.

Such a bridge would be called a 'controlled bridge rectifier' and contain at least one, probably two or four silicon controlled rectifiers (SCR) or TRIACs

 

 

If you have been reading about bridges for power control are you sure you don't mean this sort of bridge rectifier ?

I was also wondering if he meant a Wheatstone bridge, which uses a similar arrangement with resistors.

And yes, rheostats are old-school, and energy wasters ( they also don't play well with compact florescent lights, which is why if you had an home with the old rheostat type light-dimmer switches, you wouldn't want to use CFLs with them).  Some of the newer dimmer circuits use SCRs ( Silicon Controlled Rectifiers) circuits, which use duty cycle to control power to the load.

And solid state power supplies often replace the old step-down transformer, bridge-rectifier, filter, voltage regulator power supplies.

A rheostat is a variable resistor.  It controls how much current is delivered to a load.  The adjustment is made by moving a slider along to change resistance. A simple example is like this:

Light dimmers are an example, as is the heat adjustment knob for an electric range top burner.

A bridge rectifier uses diodes, which are arranged in in a manner to convert alternating current (current that alternates its direction flow rapidly) to direct current ( current the flows only in one direction.

A diagram would look like this:

D1-D4 are diodes. They act like one-way valves for electricity, letting it flow one way through them and stopping it from flowing the other. The arrangement of the diodes is such that no matter what direction the current in flowing from the source, it only flows one direction through RL.

If the source current is in one direction it passes from point A through D1 to point D then to the left through RL to point C, through D3 to point B, and then back to the source

When the source current reverses direction, it flows from point B through D4 to point D, then to the left through RL to point C, Then through D2 point A before returning to the source.

So, no matter what the direction the current flows from the source it flows through RL from right to left.

If it helps, think of the wires as streets and the ones with diodes are one-way streets,  It doesn't matter whether a car enters through A or B, it has to travel from right to left through RL.

Thus rheostats control the amount of current, and bridge rectifiers control the direction of current.

Keeping with the Star Trek theme:

And it wouldn't be complete without an A Weekend at Bernie's   reference:

My contribution to the meme:

"I'm still cold!"

P.S. This was the only good picture of a sauna that I could find that would work.   It is a bit fancy compared to the ones I grew up frequenting, which were a bit more "rustic".  They more closely resembled this:

This image is  pixelated because it is from a Youtube video and the original  was not well lit.  This is the best result I could get in lightening it up.

This particular Sauna is also a bit on the small size, as it is one for a summer cabin.  Just imagine it a bit wider and deeper, with a two tier bench rather than the single bench, and you'd have a pretty good idea of what I was used to.

20 hours ago, DrmDoc said:

I agree but I think Trump's threat is likely a veiled flexing of his potential political muscle against those Republicans who might support some future punitive action for his clearly seditious efforts against Biden's presidential confirmation.  

But anyone in the Republican party who really understands Trump also knows that Trump would expect to be the major candidate for that new party.  If you strip him of the ability to run for federal office again, you would remove his interest in forming the new party.  

2 minutes ago, J.C.MacSwell said:

Can we breath a sigh of relief yet? 

At least as far as Trump being able to pull off some last minute stunt (like declaring martial law) in an attempt to hold on to office.

9 minutes ago, StringJunky said:

Look at this EM chart:

Wifi. and mobile wavelengths are around 3metres  long and the lowest level of ionizing radiation is just into the uv range many, many times shorter. Look where visible light is, I don't think that causes ionizing radiation, so how can microwaves cause the purported issues if ionization starts and increases to  the right of the uv segment? 

Most people don't really grasp that the term "radiation" spans a huge range.  After microwave ovens came out, and people were told that they used microwave "radiation", they started to use the term "nuke" when heating things up in a microwave. After all, "radiation" is something associated with nuclear reactors and bombs.  The fact that microwaves are nearer the opposite end of the spectrum isn't commonly understood.

9 hours ago, iNow said:

Snapchat permanently banned Trumps account today, too. 

The city of New York has backed out of all contracts with the Trump organization.

Marriott and many other companies have pulled contributions from all congress people who opposed certifying Biden’s win.

I’m pretty sure Hertz just said they would even rent Trump a car and Nathan’s wouldn’t serve him a hot dog.

Okay... that last one was made up, but wow!

Josh Hawley ( The Senator who raised the objection to counting the Electoral votes even after the attack on the Capital), has also had a book deal with Simon and Schuster canceled.

Of course, he went on FOX to cry about "First amendment rights".  But this has nothing to do with that.  This was purely a business decision. The publisher simply felt that doing the book deal with him would be worse for business than the loss of profit from not selling it.  They are perfectly free to choose not to do business with someone if they feel it is in their best interest. 

This is capitalism;  Something you would think that a Republican senator would be quite familiar with.

42 minutes ago, iNow said:

What do you think about that? Is this an unacceptable obstacle to free speech?

All decisions made by private entities.  Having free speech does not obligate others to provide you with a platform from which to express it.

13 minutes ago, Airbrush said:

Does anyone think Trump can be charged with something related to his attack on the Capitol?  He incited it.  The penalties below do not take account for a murder taking place during the attack, a police officer was bashed to death with a fire extinguisher, and a woman was shot by a cop as she climbing menacingly thru a window inside the Capitol.

"A person who commits the following acts faces up to six months’ imprisonment and a $5,000 fine:

• 1 enters or remains on the floor or in the gallery of the U.S. Senate or House chambers without authorization
• 2 obstructs or impedes passage through or within the Capitol building or grounds
• 3 damages or destroys property in Capitol buildings or on Capitol grounds, or
• assaults an individual in a Capitol building or on Capitol grounds.

The penalties increase to a class E felony—punishable by up to five years in prison AND a $250,000 fine—for the following violations involving weapons, force, or violence:

1 carrying, having readily accessible, discharging, or transporting any firearm, dangerous weapon, or explosive on in Capitol buildings or on Capitol grounds, or

• 2 with force or violence, entering or remaining on the floor of either chamber."

Federal Trespassing Laws | CriminalDefenseLawyer.com

Trump was telling his supporters for several weeks to come to DC to overthrow election, and that "it's going to be wild!"

Wednesday morning Trump tells his crowd, in a rally near the White House to march to the Capitol building and "be strong" and that he was coming with them. Giuliani tells the same crowd to have "trial by combat." Trump then went home to watch it all on TV, amused.

There are legal experts that say that the attack on the Capital building could be tried for sedition and that it is almost textbook case.  It has to do with the U.S. code on seditious conspiracy which, among other things, lists "or by force to prevent, hinder, or delay the execution of any law of the United States,".    Since the intent was to stop congress form counting electoral votes as required by law, their acts pretty much fall under this.   If found guilty, they could face up to 20 yrs in prison.

The 25th amendment would probably be a more likely scenario.  It require just a majority of the cabinet and Pence to initiate. (And apparently Pence is furious with Trump, and it has been discussed by some cabinet members*.)    Pence would then take over until the inauguration. While Trump could dispute it, the dispute would have to go to Congress where it would take a 2/3 majority to reject Trump's claim.  However, Pence would remain in charge until Congress reaches a decision, and the Democratically controlled House could delay the vote until the end of Trump's term anyway.

* And while this is mere speculation, I also wonder if they could just being using the mere threat as a "check" On Trump.  He went from egging his supporters on just before the attack( "We will never concede!"), to a weak response right after, even rejecting repeated requests for him to call in the National Guard to regain control(somebody eventually did, but it's not clear who), to a condemnation of the attackers and an acceptance that Biden will be sworn in,  all over a very short period.  Could it be that someone went to him and basically said, "We have the 25th amendment ready and loaded.  And while we'd rather not use it, If you continue to force our hand, we will."

24 minutes ago, npts2020 said:

How, then, does a nuclear powered aircraft carrier go from all stop to full speed ahead in a short period of time?

Oh, I don't know, maybe by just not delivering the reactor output to the propeller?

49 minutes ago, beecee said:

Thanks for that...makes sense. But then again, why cannot the constitution be changed to suit the times? [Probably also  many other areas of it could see the USA benefit by changes] 

It can, But the amendment to do so would first have either get a 2/3 majority support in both Houses (House of Rep and Senate) or be applied for by the state legislatures in 2/3(34) of the states. In which case Congress must call a convention.

An amendment proposed by either of these means would then have to get ratification from the legislatures  of 3/4(38) of the states.

13 minutes ago, beecee said:

Can I ask a question here? Why the bloody hell, does the US leave a defeated President in office for 2 months, before installing the bloke [Biden] that defeated him? Is this something to do with the US constitution? I understand that vote counting can take some days or even weeks in certain circumstances, if counting is close...that happens everywhere. I just cannot understand for the life of me, why Trump after losing all his so called challenges, can still linger in that position, and potentially create and pass new laws and legislation that can stifle the incoming President. Can someone please educate me as to this apparent anomaly in US politics?

Yes, it is in the constitution. And remember when the Constitution was written.  Vote results had to travel by land to a centralized point in each state, then counted. Then electors selected, gathered together, and cast their votes.  These votes had to be delivered from each state to congress without any quick means to do so.  Once Congress got and counted the elector votes, they could announce the winner, who, if he wasn't already in the capital, would have to travel there to be inaugurated.    The whole process just took time, and the constitution was written to account for this.

To change it would require amending the constitution.