Why when bitcoins rises the altcoins falls?

[ShakyhandsBTCer]

When bitcoin rises it is in terms of fiat.

When alt-coins fall it is in terms of BTC.

In terms of fiat, alt-coins stay at roughly the same price.

True enough for "a few days or weeks", but some alt/usd have made stunning moves.
For example, Namecoin used to have a normal range of ~$0.40 to ~$0.70, then it exploded and went to around $10 each, which is a monster % gain for people who caught even part of the move.

Now NMC acts like it is 'dead forever', but someday...?

Personally I think that most alt-coins are really just a way that their creators are trying to get rich.

With NMC being the exception, pretty much all alt-coins do not provide any value that bitcoin does not already provide. If you are going to deal in alt-coins then you are speculating IMO (not that anything is wrong with that but speculating is not the same as investing)

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[Amph]

bcause they dump to buy bitcoin

[sagrid]

bcause they dump to buy bitcoin

agree

[bitcool]

Since the majority loses money, you have to go against the herd.

[counter]

it's simple really. people mine alts because the difficulties are much lower than that of btc. then, when btc rises, they sell off their alts to convert to btc which causes the price of the alt to drop (because of the selloff) and in turn causes btc to rise even more because people are buying it instead of selling.

Wow, I never put the miners into consideration which is something I feel silly about overlooking honestly.  The theory I had before is one I still believe but I feel the point you make is also valid then my suggestion.

miners are running a lot behind the scenes.  I am pretty sure big mining heavy hitters talk and make back room deals.  they are pumping and dumping.  alts are really a dangerous place to play.  a dev can release a coin.  the dev and friends can mine and mine.  and then once enough people are in, they can dump.  it happens over and over.

Well put jabo38.  I have just started paying some attention the the alts and I'm of the opinion that there is some manipulation taking place. 
So that does not surprise me that you'd suggest such deals taking place.  When you think of whales and miners and the potential of shady deals taking place it puts a lot of things in perspective, when looking for a alternative coin to invest in I'd say.  Not to mention the exchanges is just another aspect to take under consideration.

[Zer0Sum]

I have noticed that in terms of US Dollars both BTC and alt coins have a positive correlation.

Yes, highly correlated = 0.841...
Above is a carefully constructed semi-cap weighted Alt Index (blue) vs BTC (gold)...
That had about 12 alts summer 2013... and now 22 alts summer 2014.

A coin is not added to the above index unless it's been on an exchange for 4-8 weeks...
So you are missing all the early mining gains and listing pumps...
Even without the real action experts capture... Alts as a universe have kept up with BTC gains.

There is a concept "fooled by randomness"...
Where most people own a few alts and use the "eye test"...
Then develop this "feeling" that BTC/Alts are negatively correlated... but it's mostly lags.

[ShakyhandsBTCer]

it's simple really. people mine alts because the difficulties are much lower than that of btc. then, when btc rises, they sell off their alts to convert to btc which causes the price of the alt to drop (because of the selloff) and in turn causes btc to rise even more because people are buying it instead of selling.

Wow, I never put the miners into consideration which is something I feel silly about overlooking honestly.  The theory I had before is one I still believe but I feel the point you make is also valid then my suggestion.

miners are running a lot behind the scenes.  I am pretty sure big mining heavy hitters talk and make back room deals.  they are pumping and dumping.  alts are really a dangerous place to play.  a dev can release a coin.  the dev and friends can mine and mine.  and then once enough people are in, they can dump.  it happens over and over.

Well put jabo38.  I have just started paying some attention the the alts and I'm of the opinion that there is some manipulation taking place. 
So that does not surprise me that you'd suggest such deals taking place.  When you think of whales and miners and the potential of shady deals taking place it puts a lot of things in perspective, when looking for a alternative coin to invest in I'd say.  Not to mention the exchanges is just another aspect to take under consideration.

I have my doubts about market manulipation by the miners.

The miners have (usually) invested a lot in their machines.

IMO they would be the last set of people who would attempt to manulipate the market as market manulipation only decreases trust in the coin.

[pastet89]

Because people sell alts to cash out BTC.

[counter]

it's simple really. people mine alts because the difficulties are much lower than that of btc. then, when btc rises, they sell off their alts to convert to btc which causes the price of the alt to drop (because of the selloff) and in turn causes btc to rise even more because people are buying it instead of selling.

Wow, I never put the miners into consideration which is something I feel silly about overlooking honestly.  The theory I had before is one I still believe but I feel the point you make is also valid then my suggestion.

miners are running a lot behind the scenes.  I am pretty sure big mining heavy hitters talk and make back room deals.  they are pumping and dumping.  alts are really a dangerous place to play.  a dev can release a coin.  the dev and friends can mine and mine.  and then once enough people are in, they can dump.  it happens over and over.

Well put jabo38.  I have just started paying some attention the the alts and I'm of the opinion that there is some manipulation taking place. 
So that does not surprise me that you'd suggest such deals taking place.  When you think of whales and miners and the potential of shady deals taking place it puts a lot of things in perspective, when looking for a alternative coin to invest in I'd say.  Not to mention the exchanges is just another aspect to take under consideration.

I have my doubts about market manulipation by the miners.

The miners have (usually) invested a lot in their machines.

IMO they would be the last set of people who would attempt to manulipate the market as market manulipation only decreases trust in the coin.

Just to clarify a little, when I say miners I mean larger shady groups not everybody mining in general.  It just seems likely to me some coordinated effort to profit from others not in the know is a likely possibility.

I think they overall trust wouldn't be lost in the coin just short term trust.  When people panic sell which they tend to do the manipulators then have an advantage because they initiated the problem in the first place.